ABSTRACT. We are facing environmental challenges unparalleled in human history. Much of the attention is on climate change. It is, however, a slowly developing threat, and the full consequences will not be made manifest until the distant future. The more immediate challenge we face is related to land use-land cover change. In Florida, we have gone from a mostly natural to a largely built environment in the last 150+ years. A raindrop falling in Florida in the 19th century probably fell in a wetland and nowhere near a channel, and did not travel far before evaporating or recharging underlying aquifers. A raindrop falling in Florida today probably falls in a built landscape and close to a drainage feature, the purpose of which being to move that water and whatever it carries into the nearest major waterbody. This was all intentional – in urban areas we wanted to protect infrastructure and human health and safety and in agricultural areas we wanted to bring land into production and increase yields. We are now living with the unintended consequences, including flooding and poor water quality. There is now widespread agreement that we need to reverse these trends. However, we cannot restore all of Florida to the condition it was in the early 19th century. Though undoubtedly beautiful, that condition is not compatible with our modern ways and quality of life. Instead, we need to build a novel landscape that balances our modern ways and associated quality of life with environmental restoration and protection. That is a tremendous challenge, particularly because the pace of land use-land cover change remains unrelenting and climate change is proving to be a force multiplier. This is fundamentally an engineering challenge, one the attendees of this conference must rise to overcome.

ABSTRACT. In the Mid-Atlantic coastal region, groundwater is the main source of water used for agricultural irrigation and residential use. Warmer temperatures, shifting rainfall pattern (intermittent and non-uniform distributions), as well as increased evapotranspiration have caused groundwater withdrawals for irrigation to increase over time. In Maryland, there has been an approximate 122% increase in freshwater withdrawals from confined aquifers for irrigation and about a 48% increase in freshwater withdrawals for municipal use. These increased withdrawals have resulted in declining water levels both in Southern Maryland and in several regions in Coastal Plain. In order to protect and preserve Maryland’s water resources, there is an immediate need for a comprehensive water resources assessment. There is also a need for data-driven tools to facilitate water resources decision making. This project examines the feasibility of using historical water use data and the power of machine learning (ML) to conduct data mining and project the water demand. This uncovered data, combined with hydrodynamic modeling through SWAT, is able to estimate the stress on water resources under future climate scenarios. Preliminary data indicates the stress on water resources under current climate scenarios in Maryland and showed the regions that will most likely be under stress (hotspots) in future. Preliminary results also show promise in paving a way for proper management strategies that secure sustainable water resources for Maryland and similar physiographic and climatic regions.

ABSTRACT. The Upper Floridan Aquifer (UFA) is among the largest, most productive aquifers in the world and is a vital regional resource shared between Florida, Georgia, and Alabama. The UFA supports agricultural activities worth >$7.5 billion and supplies drinking water to more than 10 million people but faces significant threats to water quality and quantity which could potentially harm food security, fiber production, and vital ecosystem services. The USDA-NIFA funded Floridan Aquifer Collaborative Engagement for Sustainability (FACETS) project brought scientists and stakeholders together in a Participatory Modeling Process to understand the economic-environmental tradeoffs associated with alternative climate, land use, and Best Management Practice (BMP) adoption scenarios, with the goal of understanding changes needed to achieve agricultural water security and environmental protection. This presentation will highlight successes, challenges and outcomes of this five-year project including field experiments that measured yields and water and nutrient balances of alternative cropping systems and BMPS; co-developed biophysical and economic models that simulated farm/forest-scale and regional scale economic-environmental tradeoffs for current conditions and alternative future scenarios; stakeholder preference research that evaluated producer willingness-to-accept and public willingness-to-pay for incentives to achieve promising land use and/or management changes; social learning research that shaped the design and evaluated the success of the Participatory Modeling Process; and science communication research that evaluated alternative methods to frame and communicate key project messages beyond project participants.

ABSTRACT. Research on the impacts of climate change (CC) on water resources has received much attention during the past decade. However, little research has been done on how future climate will likely impact sediment transport and channel stability of first-order streams, particularly in urban environments which utilize Nature-based Solutions (NbS) for stormwater management. This study aimed to assess whether the current stormwater regulations in the state of Maryland, USA, which require the use of environmental site design (ESD), are protective of channel stability when CC is considered. ESD relies on the combination of the concepts of NbS for enhanced infiltration and evapotranspiration with the utilization of storage-based gray infrastructure. To achieve this goal, a coupled hierarchical modeling approach was developed and applied to examine projected changes in bedload transport and channel geometry for a first-order riffle-pool, gravel-bed channel draining an urban watershed equipped with the extensive implementation of ESD. The modeling approach was based on discharge from a watershed-scale hydrologic model driven by a range of spatiotemporally downscaled CC scenarios. Changes in sedimentary responses of the modeled reach were estimated using the Hydrologic Engineering Center River Analysis System 6.3 (HEC-RAS). Ensemble simulation results showed that even with the extensive implementation of ESD, the studied reach is expected to degrade over many decades developing alternate regions of aggradation and degradation due to the changes in watershed hydrology caused by urbanization under both current and future climate conditions. Mobilization of larger particles during high-magnitude storm events and their subsequent deposition upstream of narrower sections of the reach leads to the formation of several steep riffles. Results from this study show that the current stormwater regulations in the State of Maryland are not protective of channel stability and that changes in climate will likely accelerate channel degradation.

ABSTRACT. The Chesapeake Bay region has one of the highest rates of water level rise in the U.S. due to sea level rise and sinking land. Over the next 30 years, an additional 2 feet of sea level rise is expected along Maryland’s coast. Communities are already experiencing the impacts of rising water through an increase in high tide flooding events, resulting in closed roads, shoreline erosion, and threatened infrastructure. Natural and nature-based features (NNBF), such as marshes, dunes, and living shorelines offer a win-win solution by buffering people and infrastructure from water and waves while providing valuable wildlife habitat and water quality benefits. To elevate the use of NNBF as a climate adaptation strategy, the Maryland Department of Natural Resources (DNR) launched a Resiliency through Restoration Initiative in 2017 to implement and monitor innovative restoration projects throughout the state. The Chesapeake Bay National Estuarine Research Reserve developed monitoring protocols and partnered with University of Maryland Center for Environmental Science to collect field data (elevation, vegetation, accretion, and sediment) at priority sites and evaluate project effectiveness. Additionally, DNR partnered with George Mason University and The Nature Conservancy to study wave attenuation and flood reduction benefits of marshes and evaluate the impacts of sea level rise on those services. The project team collected field data (hydrodynamic, vegetation, and topo-bathymetric), ran coupled local and regional hydrodynamic and wave models (ADCIRC + SWAN, XBeach), and worked with Warren Pinnacle to rerun the Sea Level Affecting Marshes Model (SLAMM) to better understand how sea level rise will impact the wave attenuation capacity of marshes in the future. Results from these comprehensive monitoring and research efforts are directly informing site-level adaptive management activities, statewide restoration implementation guidance, and statewide conservation and restoration priorities. This presentation will address how research is informing climate adaptation.

ABSTRACT. The water quality benefits of constructed treatment wetlands have been widely-studied and reported upon. This has led to increasing adoption of treatment wetlands to manage a variety of water quality challenges. Conversely to treatment systems that rely on external sources of energy and chemicals (wastewater facilities and water treatment plants), constructed treatment wetlands rely primarily on the sun and natural processes for water quality improvement. Because of the low-energy nature of wetlands, these systems rely on surface area rather than external energy inputs to achieve desired levels of treatment. Furthermore, these constructed treatment wetlands are generally fed by a continuous source of water. The large footprints of these systems, when combined with a consistent water source, often makes these constructed wetlands unique habitats within the landscape. These habitats attract wildlife with specific, wetland dependent needs; and when open to the public, humans. This has resulted in substantial ancillary benefits associated with constructed treatment wetlands and an additional driver for these projects to be adopted. This presentation will present information on bird utilization of constructed treatment wetlands in North Central Florida based on data derived from a large, citizen-science dataset. For systems that are open to the public, these data are presented with estimates of visitor attendance to provide a clearer picture of the value of these natural treatment systems to both wildlife and humans.

ABSTRACT. In 2017, the largest groundwater recharge wetland in the world, known as the 4G Ranch Wetlands, was constructed in Florida. Groundwater recharge wetlands are constructed wetlands that do not have a surface water outflow and water is applied at the rate of infiltration to the underlying aquifer. The 4G Ranch Wetlands serve as a wet-weather management solution for Pasco County’s reuse system and recharge 5 MG on annual average to the aquifer system. Located in an area suffering prolonged drawdown by regional wellfields, the 4G Ranch Wetlands also restore nearby hydrologically-altered lakes and wetlands.

Through a public-private partnership, the 4G Ranch was identified as a suitable site for the infiltration wetland. The 176-acre 4G Ranch Wetlands are comprised of 15 individual cells that are operated via water level measurements and flow control valves. Driven by the 4G Ranch’s desire to use the system for recreation, the wetland system includes several ecological design features and a mosaic of wetland habitats.

The wetlands have been in operation since 2017 and water levels of each wetland cell are adjusted seasonally to achieve healthy wetland hydroperiods and encourage the growth of desirable wetland species. Since operation, the 4G Ranch wetlands have been monitored for the success of the planted wetland vegetation establishment, the rate of infiltration, nitrate reduction, and presence and diversity of wildlife. This presentation presents the wetland design and an update on the success of the overall wetland system following six years of operation.

ABSTRACT. Despite being marketed as wholly green and sustainable solutions, contemporary commercial floating treatment wetland (FTW) models rely heavily upon nonbiodegradable components (i.e., plastics and metals). These non-natural materials can create “ecological traps” and/or contribute to macro/microplastic pollution. Approaches meant to improve water quality and habitat should not be simultaneous sources of habitat and water quality degradation. Natural floating wetlands occur within multiple ecosystem types across multiple continents (e.g., Typha spp. tussocks in Florida, floating Carex spp. fens in Alaska, Panicum hemitomon-dominated floating marshes of the Mississippi River delta, Cyperus papyrus marshes of equatorial Africa) as either relatively stable communities or ephemeral rafts. Therefore, it should be possible to engineer fully biodegradable FTWs which emulate and provide similar services as these natural systems. Typha spp. shows special promise, as it can form physically stable, autobouyant, and productive natural floating wetlands which provide significant habitat and water quality benefits in a wide variety of climates and hydrologic settings. These next-generation, ecofriendly platform designs are critically needed if FTWs are to realize their potential in an increasingly urbanizing world requiring a broad spectrum of water quality protection and habitat provisioning solutions.

ABSTRACT. This case study showcases the use of Unmanned Aerial System (drone) aerial imagery for vegetation monitoring at the 4G Ranch Wetlands. This seven-time award winning groundwater recharge wetland project consisting of 15 constructed wetland cells with a total area of 176 acres was planted and began operation in 2017. This treatment wetland was designed to maintain between 4 and 24 inches of inundation seasonally and support healthy native habitat mosaics. Vegetation monitoring occurred twice a year for three years (2018-2020) during the dry and wet seasons to monitor the establishment and succession of planted native vegetation communities and to inform recommendations for changes to operational depths within the wetland cell. Monitoring was conducted using aerial photography with the use of drones to provide high definition orthomosaic photography. Aerial mapping and photo processing were used to capture photography with detail up to 0.08 cm/pixel. GIS analysis coupled with onsite ground truthing provided detailed characterization by community and overall vegetation area coverage in each cell. GIS analysis was utilized to characterize vegetation community growth over the monitoring period and to quantify vegetation establishment. Analyses included calculation of percent coverages of planted communities as well as establishment of invasive and recruited species. First year dry season results revealed an overall average vegetation cover of only 19%. Second year dry season monitoring results showed an average vegetation cover of 39% cover. Third year dry season monitoring results showed an average vegetation cover of 43%. The recommendations provided based on the vegetation surveys resulted in more vegetation coverage and precise control of exotic species. This presentation will provide a summary of the technology used to conduct fast and precise vegetation surveys, the results of the three-year study, and how vegetation surveys can inform operational changes.

ABSTRACT. Chlorophyll, the photosynthetic pigment found in both plants and algae, provides a way for algae quantification in water quality assessment. Within this study, a dual biological-chemical treatment strategy was implemented with the use of floating treatment wetlands (FTWs) and lanthanum air-lift pumps. Nitrate is removed via FTW plant uptake and microbial denitrification while phosphate becomes bound to lanthanum and precipitates out of the water column. The study site, Densmore Pond, had one FTW installed in 2020 and a second FTW installed in 2021 along with two lanthanum air-lift pumps. It is believed that a reduction in both nitrate and phosphate will stunt algae growth. To assess algae content, the European Union’s Sentinel-2 satellite was utilized to quantify chlorophyll. Sentinel-2 has been shown to accurately detect chlorophyll in larger water bodies but may struggle with smaller ones. Water samples were collected at three georeferenced locations spaced at least 10 meters apart every two weeks at Densmore Pond. Google Earth Engine was utilized to calculate band ratios to create a relationship for chlorophyll content. What was found is that the band ratio using the blue band (490 nm) and green band (560 nm) performed the best at creating a correlation to chlorophyll concentration. A coefficient of determination produced a value of R2 = 0.38. Running this band ratio for Sentinel-2 images from 2016-2022, a Tukey’s post hoc test was used to test for differences between years with respect to each month. Running the Tukey HSD test, 2017 and 2021 showed a statistically significant decrease in chlorophyll in comparison to all other years. In 2021, Densmore Pond produced a mean band ratio of 0.55; lower than all other years analyzed. Likewise, for each individual month, it was observed that the chlorophyll concentration in 2021 was significantly lower for May, July, August, and October.

ABSTRACT. The large Prado constructed treatment wetland was primarily designed to remove nitrate from the effluent-dominated Santa Ana River. Up to half the river’s discharge of 224 cfs is diverted thought 23 cells of the 188-ha treatment section and clean water is returned to the river a few days later. Downstream, the river is infiltrated in the groundwater and, with further treatment, becomes part of the drinking water supply for about 2.5 million people in Orange County, CA. The treatment wetland has been operating since 1998. I report long-term differences in inflow and outflow for 32 variables. Not all were reduced after wetlands treatment, and some were often below detection in the inflow. Substantial removal was found for Cu, Zn, Cr, Pb, Hg, Fe, and Al, but dissolved Mn and Ni doubled (though still at low levels). As, B, Br, Se, and conservative parameters like halides, Ca, CaCO3, and SO4 changed little (2-10%) a concentration attributable to evapotranspiration. Turbidity doubled probably due to the shallow little vegetated lower ponds. DO was lower than inflow but rarely dropped below the standard of 5 mg/L. The wetland increased the low levels of turbidity, DOC, DON, and had little effect on pH. Temperature inflow versus outflow was unchanged but showed a long-term warming only for the inflow (river) but not for the wetland outflow, indicating a major benefit of wetlands in for temperature-challenged fish like salmonids.

ABSTRACT. Wetland ecosystems are highly productive ecosystems that sequester high amounts of carbon and retain and remove nitrate from agricultural runoff. Yet, the anaerobic conditions that drive carbon sequestration and denitrification can also promote high rates of methane production. The rate of methanogenesis and overall methane fluxes are highly variable across individual wetlands. However, the factors driving this variation are unclear. Plant community composition has the potential to modulate methanogenesis and denitrification, providing opportunity for improved management. Further, wetlands near agricultural fields are unique in that some can receive high sulfate concentrations, which can decrease methane production by modulating redox conditions. How agricultural runoff and plant community composition interact to drive overall rates of denitrification and methanogenesis are unclear. Such information will improve guidance for plant community selection and water quality management that promote high levels of denitrification while minimizing methanogenesis. We studied water quality and gas levels of three Indiana wetlands near West Lafayette, Indiana from August 2021 to August 2022. These wetlands are closely associated with runoff and tile drained agricultural fields. One wetland had high levels of sulfate and was dominated by invasive reed canary grass (Phalaris arundinacea). Sulfate concentrations were lower and native plants were dominant in the other wetlands. Based on differences in carbon composition between wetlands, we hypothesized that carbon released by reed canary grass was driving differences in methanogenesis alongside sulfate concentrations. To test these observations, we conducted microcosm studies, which aimed to identify conditions that minimized methane and nitrous oxide concentrations while maximizing denitrification rates in wetland soil cores using additions of reed canary grass leachate and sulfate in a factorial experimental design. We present the results of this experiment and relate findings to wetland nutrient levels, plant community composition, and hydrology. These findings will inform more effective and efficient wetland management.

ABSTRACT. NC State University evaluated Charlotte-Mecklenburg Storm Water Services’ (CMSWS) water quality data for the period of 2007 to 2020 to identify trends and future monitoring, management and planning decisions to protect and restore urban streams. Pollutant concentrations and loads were compared among monitoring sites and to relevant state standards. Point source and nonpoint source loads were also compared. Trends were analyzed using the US Geological Survey’s WRTDS regression method, which accounts for variations due to time, discharge and season. The Soil & Water Assessment Tool (SWAT) and EPA’s Spreadsheet Tool for Estimating Pollutant Loads (STEPL) were used to develop total nitrogen and total phosphorus loads for select watersheds to see how well the predicted loads matched the loads calculated from measured water quality and flow. Most water quality parameters were below regulatory standards with the exception of copper, fecal coliform and nitrate. Copper was exceeded in ~80% of the sites with over 80% of the exceedances occurring during stormflow. Fecal coliform exceeded the aquatic life standard in about 80% of the samples. Nitrate levels were a concern in all watersheds with major wastewater treatment plants, which were estimated to account for 75% of the TN load and 47% of the TP load in the study area. Land cover change was significant to changes in channel flow events and macroinvertebrate metrics. Findings of this effort including recommendations for how CMSWS could modify their sampling program to improve the value of the data for management purposes will be reviewed in this presentation.

ABSTRACT. Urbanisation has dramatically increased impervious surfaces resulting in increased peak volumes of urban stormwater. Metal roofs are a large contributor of heavy metals, which are considered priority pollutants of concern for urban streams in many cities. Zinc and copper are prevalent in roof runoff in New Zealand as they originate from the dissolution of galvanised steel and copper sheet roofing widely used in the country. Most of these metals are found in a dissolved form, which is difficult to remove with conventional treatment systems that are primarily aimed at removing particulates. Therefore, a Downpipe Treatment System (DTS) containing waste seashells, named the StorminatorTM, was developed to remove a significant amount of dissolved metals from roof runoff prior to it reaching the stormwater network. This study conducted at University of Canterbury in Christchurch investigates the long-term efficiency of the cartridge media in the StorminatorTM from different metal roof types (galvanised steel, copper and Zincalume®) during four different seasons (one year of sampling) to investigate the change in the StorminatorTM removal efficiency during different climate characteristics and metal roof types.

Results showed that the StorminatorTM successfully removes dissolved Cu and Zn concentrations from all metal roof types (i.e., between 60-97 percent). Metal roof types and climate variables can influence the roof runoff characteristics. Correlations were found between antecedent dry days and inlet concentrations (R2=063, R2=0.59, R2=0.53 for galvanised steel, Zincalume® and copper roofs, respectively), suggesting that dry days period allows contaminants build-up from atmospheric deposition, contributes to weathering and degradation of the metallic surfaces and increases leaching rate. StorminatorTM has demonstrated its effectiveness to remove dissolved Cu and Zn from roof runoff in a very short hydraulic time (>39m/hr-y min), and potential benefits as a sustainable and cost-effective DTS.

ABSTRACT. Over 50% of the water consumed by Florida households is used for turfgrass irrigation, stressing the need for research on water conservation opportunities within residential landscapes. Natural soils become degraded and compacted during the construction of new homes, but soil quality can improve over time or through the incorporation of soil amendments. The objective of this study is to characterize how amending soils under lawns with different types and rates of compost allows for reduced irrigation. Bulk soil samples were taken from study plots of St. Augustine grass grown in amended and unamended soils to determine soil moisture characteristic curves for each amendment rate and type. The turfgrass quality was also evaluated for each of the 72 plots on at least a monthly basis. The turfgrass will be evaluated on a quality rating scale from 1 to 9, with 1 being the poorest quality and 9 being the best or highest rating and 5 being the minimum acceptable value for homeowners. Preliminary results show improvements to turf quality were observed in plots that received the medium (161 m3 ha-1) and high (323 m3 ha-1) soil amendment rate compared to the unamended controls. The highest amendment rate remained above the minimum turfgrass quality rating for irrigation rates 50% of the recommended rate and above. This study suggests that compost incorporation of at least the medium soil amendment rate could provide an opportunity for irrigation reductions from currently recommended rates.

ABSTRACT. Tire wear particles (TWPs) have been implicated as the source of 6PPD-quinone, a recently discovered chemical that is acutely toxic to coho salmon (Oncorhynchus kisutch). TWPs deposited on roads are transported to aquatic ecosystems via stormwater where they contribute to microplastics pollution and organic contaminant loads. Green Stormwater Infrastructure (GSI) provides an opportunity to prevent TWP release, however little is known about the fate of TWPs and their leachable contaminants in these systems. We conducted three experiments to quantify the treatment performance of permeable pavement (PP) formulations, a type of GSI, for TWPs and 10 tire-associated contaminants including 6PPD-quinone. The PPs comprised concrete, and asphalt, with and without cured carbon fibers used to improve the mechanical properties of the PPs. Pavements had underdrain pipes draining to effluent sampling ports and were artificially dosed. Three sequential experiments were conducted to evaluate PP mitigation of tire-associated pollution. The 1st and 3rd experiments established a baseline for TWPs and contaminants and evaluated the potential for continued pollutant release during subsequent storms, respectively. During the 2nd experiment TWPs were applied to each pavement. Our results showed that the PPs attenuated >99% of the deposited TWP mass, with <1% of particle mass escaping the pavements during two simulated storms following TWP deposition. PPs prevented an estimated 72-99% of potentially leachable 6PPD-quinone from being released into the effluent. All PPs performed equally well in terms of TWP and chemical treatment. Our results suggest that PPs may be an effective form of GSI for mitigating tire-associated stormwater pollution. The improved strength of cured carbon fiber-amended pavements could allow PPs to be deployed on high-traffic roadways where tire-associated pollution poses the greatest environmental risk.

ABSTRACT. Bioretention systems, a form of green stormwater infrastructure (GSI), apply the concept of biomimicry by using engineered soil media to capture and convert pollutants found in stormwater, before they reach downstream water bodies. The inclusion of bioretention systems in developed landscapes offers a potential solution to urban water quality issues. This study explores the use of woodchips, sourced from hardwood, and aluminum-rich drinking water treatment residuals (DWTR) as soil amendments in bioretention systems. Twelve bioretention mesocosms, with three replicates each of four “soil media” treatments (sand-only, topsoil+sand, topsoil+sand+woodchips, and topsoil+sand+DWTR), were subjected to simulated stormwater events, and the water collected post-system filtration was evaluated for the removal of nutrients and heavy metals. Differences in effluent pollutant concentrations from the synthetic runoff gives insight into the effectiveness of the soil media amendments. Plant health, compared between soil treatments, was also assessed using measurements of vegetation height and percent green cover of the systems’ surfaces.

Bioretention mesocosms containing woodchips, intended to reduce nitrate output, yielded lower nitrate and total nitrogen (TN) values in the effluents compared to the control cells (topsoil+sand treatment). Bioretention mesocosms containing DWTR, intended to capture and reduce phosphorus loads, yielded lower soluble reactive phosphorus (SRP) and total phosphorus (TP) levels than the topsoil+sand control. Preliminary findings indicated heavy metal (zinc and copper) reductions in all four treatments. There were no differences in plant growth/survival among mesocosms (three treatments) that contained topsoil; however, there was a difference between the topsoil-amended and sand-only bioretention systems, with sand-only cells showing lower plant heights and percent vegetation cover.

This project, funded by the Lake Champlain Basin Program, is a partnership between the University of Vermont (PI: Dr. Stephanie Hurley, and M.S. Candidate Samantha Brewer, Ecological Landscape Design Lab, Plant & Soil Science) and Stone Environmental, Inc.

ABSTRACT. Blueprint Columbus is an effort by the City of Columbus, Ohio to improve sewer infrastructure and reduce SSO occurrences and volumes. The project includes four changes to existing infrastructure: (1) green infrastructure (GI) retrofits including bioinfiltration, and permeable pavement, (2) installation of sump pumps, (3) redirection of downspouts to GI, and (4) lining of sanitary sewer laterals to reduce infiltration and inflow of stormwater. To determine impacts of these chanages a paired watershed approach was applied in which a control sewershed, without GI, was compared to three treatment sewersheds with 208 bioretention cells and 8,400 m2 of permeable pavement. These areas were monitored with rain gauges and automated samplers during 170 storm events from 2016 to 2019 in Columbus, Ohio, USA. Decreases in stormwater flow were indicated with significant decreases in runoff depths and peak flow rates (35–62% and 40–58% respectively) and increases in lag-to-peak (6–64%) were observed in the treatment sewersheds following the installation of GI retrofits. Compared to the control sewershed, the treatment sewersheds had slight increases (1–3 mm) in runoff thresholds and lower runoff coefficients post-GI. For water quality, significant reductions in particulate and dissolved nutrients as well as sediment were observed following the installation of GI in both treatment watersheds compared to the control. Total nitrogen (TN), phosphorus (TP), and TSS concentrations decreased by 13.7–24.1%, 20.9–47.4%, and 61.6–67.7%, respectively. Runoff attenuation by GI contributed to pollutant load reductions of 24.0–25.4% (TN), 27.8–32.6% (TP), and 59.5–78.3% (TSS). These responses indicate that sewershed-scale GI implementation successfully mitigated peak flow rates, and reduced runoff event mean concentrations and loads at the watershed-scale. This is one of first results demonstrating effectiveness of stormwater green infrastructure at a watershed scale.

ABSTRACT. To achieve ecosystem recovery within degraded coral reef habitats, coral restoration practitioners must achieve a net gain in reef functionality through both protection and active repair. However, there is currently little known about the ecological functionality of restored reef ecosystems due in combination to the field’s infancy and the constraints associated with performing long-term post-restoration monitoring. The objective of this study was to monitor changes in net ecosystem metabolism (NEM) at coral reef restoration sites to comprehend ecological benefits of restoration interventions, as well as provide a baseline from which long-term ecosystem function impacts can be assessed. For coral reef restoration projects with the goal of slowing reef erosion and increasing resilience, assessing changing metabolic footprints, such as changes in calcium carbonate production in response to ecological engineering interventions, would help evaluate progress towards these goals. Here, we provide high-resolution measurements of net ecosystem calcification (NEC) and net ecosystem production (NEP) for two reefs in the lower Florida Reef Tract. Observations were made prior to and immediately following Acropora cervicornis fragment outplanting, using the Benthic Ecosystem and Acidification Measurement System (BEAMS). Both reefs originally contained near 1% hard coral cover, and the restoration effort initially increased this hard coral cover to ~10%. While comparisons of pre- and post- outplanting NEC:NEP ratios and diel trends did not indicate immediately detectible changes in NEM dynamics following coral outplanting, the authors recognize that NEM measurements collected over multiple years at these sites are needed to effectively assess the impacts of these restoration interventions and start mapping each reef’s recovery trajectory. The baseline ecosystem metabolism rates reported in this study can be used to evaluate progress toward long-term coral restoration goals and inform future restoration strategies, while helping us learn about the novel coral reef ecosystems created through coral restoration interventions.

ABSTRACT. Coastal dune restoration efforts have been escalating globally as a way to protect valuable infrastructure from rising seas and increasing storms. However, restored dunes vary widely in their ability to establish resilient systems and have notoriously high failure rates. Traditional dune restoration involves the planting of a single dominant grass species across the entire dune face, disregarding the high native diversity in these systems, stressful conditions that are common after restoration, and natural recovery pathways. Here, we evaluate if dune restoration outcomes can be improved by planting early successional pioneer species. We test if the facilitation model of succession, where pioneer species enhance the establishment of climax species by ameliorating stressors, applies to sand dunes and if this natural recovery pathway can be harnessed to increase dune restoration success. Field surveys of Southeastern US dunes suggest that Panicum amarum is commonly found in disturbed areas, suggesting it acts as an early successional species. A planting experiment revealed that stem production of the dominant dune grass Uniola paniculata is enhanced by 37% over one growing season in the presence of Panicum, while Panicum growth is suppressed by 40% in the presence of Uniola, confirming their respective roles as pioneer and climax species. An additional field experiment aimed at evaluating the optimal Panicum density that maximizes Uniola growth suggested low densities of Panicum surrounding Uniola may increase stem production within several months. However, storm surge in two consecutive years hindered our ability evaluate succession over a longer time scale. These results suggest that planting early successional species in addition to or prior to planting climax species may increase the growth rate of dune building grasses, which is critical for establishing resilient, high-functioning dunes. However, in systems with frequent disturbances, the successional trajectory is hindered, and additional restoration measures may be required.

ABSTRACT. Among coastal managers, interest in leveraging suspension feeders, such as sponges and marine bivalves, to exert top-down control on organic matter loading in estuaries is gaining momentum. Not only can these faunal engineers alleviate the consequences of nutrient pollution, but they may also bolster the critical, highly valued carbon sequestration services provided by vegetated coastal ecosystems – a potential dual effect of suspension feeders in mitigating cultural eutrophication and climate change. Ribbed mussels, Geukensia demissa, offer a useful model for better assessing faunally driven carbon and nitrogen processes in these systems and how these processes relate to density within and among aggregations of these organisms. Combining bulk geochemical analyses with Bayesian stable isotope mixing model frameworks (MixSIAR), we quantified the effects of mussels on the composition and biomass of organic C and N in material transported to the benthic floor (i.e., sedimentation) and accumulated in surface sediments in a Georgia salt marsh. This approach revealed that mussel presence locally amplified sedimentation, but not accumulation, of both externally- and internally derived organic biomass relative to areas without mussels and that both sources of accumulated organic biomass increased with increasing local mussel density. We also measured the effect of mussels on carbon and nitrogen storage in aboveground smooth cordgrass (Spartina alterniflora) and found that this biomass was strongly and positively correlated with both mussel presence and local density, a pattern largely driven by mussel-boosted macrophyte production. Lastly, we found that neighboring mussel density did not affect carbon and nitrogen accumulation and storage processes in adjacent non-mussel areas. Overall, this work provides new evidence that faunal engineers bolster the capacity of coastal systems to sequester carbon and nitrogen, demonstrating that suspension feeding bivalves interact synergistically with primary producers to enhance the blue carbon services of marshes and counteract coastal eutrophication.

ABSTRACT. Coastal environments are uniquely vulnerable to climate related impacts (e.g., storm surge, inundation, sea level change) and therefore require careful planning and management to protect communities and valued resources such as coastal habitat. Nature-based solutions (NBS) provide unique opportunities to enhance coastal flood resilience and habitat protection. Some options include the conservation and enhancement of habitat using Natural and Nature-Based Features (NNBF), the use of sediment beneficially, and the integration of NNBF elements into hybrid infrastructure designs. These solutions align with the Army Corps of Engineers (USACE) Engineering with Nature® (EWN®) initiative, and the beneficial use of dredge material (BUDM) mandate to achieve 70% BUDM by the year 2030 (“70/30 Goal”). However, there are many challenges to overcome to meet these objectives. Therefore, the goal of this study was to document NBS practices in coastal Louisiana, USA that successfully applied innovations to achieve multiple benefits while executing the Corps’ navigation mission. Specifically, two studies areas were highlighted that successfully demonstrated the full array of environmental, economic, and social impacts using beneficially used dredged sediments. These projects include 1) creation of bird islands in Baptiste Collette Bayou, and 2) coastal marsh habitat restoration in West Bay. As documented in these project examples, BUDM continues to increase and now is recognized as a critical resource in building large-scale (estimated multi-billion dollar) efforts to mitigate land and habitat losses along the U.S. Gulf coast. Overall, BUDM is being used to more sustainably execute the USACE navigation and ecosystem restoration missions while increasing the resiliency of waterborne transport infrastructure and the communities that rely on them. In turn, these data and lessons learned can be implemented elsewhere to advance coastal resiliency practice and provide inspiration for future applications of NBS.

ABSTRACT. Blooms of the marine dinoflagellate Karenia brevis (“red tide”) occur almost annually along Florida’s Gulf Coast, killing fish and marine mammals, contaminating shellfish, and causing human respiratory irritation. There is growing evidence that blooms are a consequence of both oceanographic and watershed processes, however, questions about the drivers of intra- and interannual bloom severity, extent, and durations remain unanswered. Specifically, studies suggest that K. brevis blooms begin offshore in the Gulf of Mexico and are transported inland by wind and currents, where they are likely fueled by terrestrial nutrient loading. To better understand the role of watershed fluxes in bloom dynamics, we take advantage of the observation that red tide blooms periodically affect the entire Florida west coast in some years, while in other years, blooms proliferate in some estuaries and not in others. This work applies empirical techniques to connect observed patterns between bloom occurrence, severity, and extent with corresponding environmental variables. The first objective was to define the bloom boundaries, justifying the association between bloom events and associated contributing riverine fluxes. After providing evidence of bloom spatial boundaries, the extents can be used to calculate a monthly estuary specific bloom severity index (BSI). BSI will be utilized to collate the sampling data into a continuous metric that succinctly defines the initiation, magnitude, extent, and duration of the blooms. The continuous BSI metric allows estuary specific bloom events to be characterized and compared. BSI can then be used as a response variable for the classification of hydrologic and oceanic variables regimes (streamflow, nutrient loading, and Loop Current position) that are linked to the different interannual bloom extent patterns in the different estuaries.

ABSTRACT. Excess nutrient loads from cropland, poor sediment controls, and historic wetland conversion to cropland and diked duck ponds has largely eliminated ecosystem nutrient uptake and sediment trapping services historically provided by coastal wetlands. As a consequence, Harmful Algal Blooms (HABs) frequently occur in the summer, creating human health concerns, fish kills, and a host of other problems. As a consequence of this situation in Sandusky Bay, Maumee Bay, and other coastal areas in Ohio, the State of Ohio has recently established the H2Ohio Program, aimed at improving aquatic resources, beginning with water quality. While the projects covered in this poster are all “In Bay” solutions, the H2Ohio Program is also investing in upland restoration interventions, including floodplain reconnection, wetland restoration, agricultural BMPs, and other approaches directed at reducing nutrient and sediment export to coastal waters. Biohabitats, and our partners Baird Engineering and TetraTech, have worked on several living/nature-based shoreline projects in Sandusky Bay as a result of these efforts to improve aquatic resource conditions. The variety of project designs developed include upland anchored living/nature based shorelines; offshore coastal barrier islands sheltering coastal wetlands; delta-forming designs at stream inflows to the lake that passively trap sediment and support the development of wetlands; offshore islands that reduce wave and current energy and support development of flow through wetlands and shallow water habitats; and a variety of other restoration elements (e.g., Wave Attenuation Devices [WADs], improved hydrologic connections in diked coastal wetlands, reconnection of streams to riparian wetlands, etc.). The designs are supported by incorporation of existing data, collection of additional site information, modeling of design effects (hydrology and hydraulics, wind wave and current attenuation, sediment particle transport, nutrient assimilation, wetland community development, etc.), establishment of performance and monitoring metrics, and projected cost benefit analysis.

ABSTRACT. Wetlands are a great tool to improve water quality while providing natural wildlife habitat and recreational opportunities. They have perfect conditions to remove many pollutants through physical processes, chemical reactions, microbial activity, and plant uptake. However, wetlands with elevated organic matter loading could negatively impact water quality by enhancing anaerobic microbial reactions that liberate pollutants. Such is the case for methylmercury (MeHg), a bio-accumulative pollutant, produced mainly by sulfate-reducing bacteria. MeHg poses a health risk for wildlife and humans due to its neurotoxic and carcinogenic characteristics. Cache Creek Settling Basin (CCSB) is a constructed wetland designed to trap mercury (Hg)-contaminated sediments before reaching the ecologically-sensitive Sacramento-San Joaquin Bay Delta in California. We studied the effects of organic matter addition (none, 0.025, 0.05, 0.1, 0.2, 0.4, and 0.5 g) in the form of spirulina powder on the Hg cycling in CCSB soils (~300 ppb total mercury) and water using 16-day batch water/soil (150 ml/50 g) incubations. While some analyses are still pending, preliminary results show that low organic matter addition (none, 0.025 and 0.05 g) did not stimulate MeHg production, as they were poised at manganese reduction (~100 mV redox). In contrast, at very high organic matter addition (0.4 and 0.5 g), MeHg exhibits a very high but ephemeral production due to low Hg-bioavailability and demethylation potential under highly reduced conditions. We anticipate that intermediate organic matter addition (0.1 and 0.2 g) will yield a moderate but steady MeHg production, initiating a “hot moment” of ecological significance. Results highlight the non-linear response of MeHg cycling in aquatic environments under increasing organic matter loadings with important implications for wetland management.

ABSTRACT. Flash pyrolysis GC MS was used to separate components of DOC for inflows and outflow of small test wetlands (6,250 sq ft, 2-day HRT) planted with native bulrush (Scirpus) and located within the 400-acre Prado constructed treatment wetland. The big wetland was designed to remove nitrate from the effluent-dominated Santa Ana River, but other chemicals are removed too. Reduced by the wetland were: chloronitrobenzene (used in rugs, agricultural and rubber chemicals, oil additives), alkane nitrile (residue of synthetic rubber products like disposable gloves, gaskets, seals, and tubing), propanoic acid (anti-fungal agent), tetrahydropyridine (natural human metabolite), heptanal (perfume ingredient with plant origin), tribromomethane (a DBP), and nitrobenzene (poisonous precursor to aniline used in dyes and rubber). Over 4 years, in the large wetland, chlorate – a disinfectant, weed killer, and explosion accelerator was reduced by 51% but there was an upward trend in the inflow). Study of fate of the removed chemicals was not funded.

ABSTRACT. Bioretention effectively mitigates the harmful effects of stormwater runoff. However, nitrogen removal is a consistent problem, particulary for dissolved species like NO3-NO2. Additionally, bioretention soil mix (BSM) amended with compost often leaches nitrogen, making the system a nitrogen source rather than a sink. Previous work showed that nitrogen leaching dissipates with system age and when compost content is reduced. Several design modifications have been proposed to enhance removal pathways like microbial denitrification by creating anoxic zones, but studies report varied removal rates. In this study, we evaluated nitrogen removal in bioretention systems equipped with orifice outlet controls. While these controls primarily reduce outflow rates, it is expected that nitrogen removal would increase due to possible anoxic conditions induced by flow restriction. The study consisted of six field-scale bioretention mesocosms with two outlet configurations (restricted/free-draining) and three bioretention soil mix (BSM) types (compost, aged-compost, and no-compost). Six synthetic storms were conducted to measure nitrogen removal performance. Soil moisture sensors were deployed to ascertain soil saturation and hydraulic retention time. Soil samples were analyzed with qPCR for target genes nirK and nirS which indicate denitrification activity. The effect of outlets, age, and compost content were assessed for each response variables. Outlet control had a significant effect (p<0.05) on effluent nitrate concentrations for mesocosms with the aged-compost BSM, whereas the compost BSM leached nitrate. Leaching in the compost BSM was significantly more than in the aged-compost, but this gradually reduced even within this study of six storms. The no-compost BSM had the lowest effluent concentrations and therefore the best performance. Outlet control did not significantly change nitrogen treatment for the no-compost BSM.

ABSTRACT. The microbiome of plants is important to plant growth, health, nutrient uptake, and response to stressors such as pollutants. Interactions between plants and their microbiomes are predominantly regulated by plant exudates, chemical compounds released from plant roots. This presentation will summarize research focused on determining what changes, if any, occur in the exudate profile of a model aquatic plant, duckweed, with and without its natural microbiome. Duckweed will be harvested from sources near Lansing, MI. The microbiome associated with a subsample of the harvested duckweed will be determined through DNA extraction and genomic analysis. Prior to laboratory culture, one-half of the harvested duckweed will be sterilized and cultured axenically, while the remaining duckweed will be cultured without sterilization. The exudate profiles for the sterilized and non-sterilized duckweed will be assessed after approximately two weeks of culture. The media will be replaced after one week, allowing for one week to accumulate exudates for analysis. The media and exudates will be concentrated though solid-phase extraction prior to analysis by LC-MS on the Thermo Q-exactive UPLC/MS/MS. Progenesis metabolomic software will be used to examine differences between exudate profiles. Exudate metabolomic analysis is expected to (1) determine the effects the presence of a microbiome has on duckweed exudates and (2) identify key exudates in the interactions between duckweed and its microbiome. Future studies with the goal of expanding the understanding of the relationship between the duckweed microbiome and its exudates will utilize the protocols developed in this work.

ABSTRACT. Despite deployment of stormwater treatment systems, urban watershed quality remains poor and restoration projects often struggle to meet their goals. The performance variability of stormwater treatment systems is often questioned and as a result, strict monitoring and testing protocol exist both domestically and internationally. Three sources of variation affect the performance of stormwater treatment systems: pollutant load, treatment system condition, and monitoring methods. To quantify the importance of the three sources, a Jellyfish® membrane treatment system was monitored at the University of Canterbury in Christchurch, New Zealand. The monitoring consisted of flow-proportional auto-sampling over 12 unique storm events during two maintenance periods and individual water quality samples were processed for TSS and heavy metals to calculate an event mean concentration (EMC). Flow through the unit was monitored by a contactless radar unit (RavenEye) and presence of internal bypass with a level logger. The maintenance regime was found to most affect the unit’s performance, as clogging following an extreme event caused most subsequent flows to bypass, three months prior to its scheduled maintenance. This indicates that temporal based maintenance scheduling does not adequately respond to the actual condition of the treatment system, where large events or cumulative treated loads can require more immediate servicing. The catchment’s contaminant of concern, dissolved zinc (76 µg/L average), varied throughout each storm and was most affected by total depth and duration of rainfall. Flow proportional auto-sampling across the entire event improved the quantification of EMCs. Overall, variability in treatment system performance should be expected due to the inherent inter- and intra-event variability in stormwater itself. However, this investigation further demonstrates the importance of maintenance to maximise treatment potential and suggests that temporal based schedules are inadequate and should account for accumulated contaminant load and extreme weather events.

ABSTRACT. Peat moss is a primary component of horticultural potting mixes, but the process of mining it is highly destructive to wetlands and results in the release of vast quantities of CO2. We argue that a cattail (Typha spp.) bioproduct could provide a suitable alternative. Cattail harvest offers a means to recycle nutrients, enhance waterfowl habitat, and prevent nitrogen and phosphorus saturation, but rarely occurs due to a paucity of economically viable uses. Here, we propose a Typha-derived bioproduct that could serve as a peat moss substitute, thus replacing a product that degrades wetlands with one that enhances them. Typha potting media will be evaluated for the physical and chemical characteristics that determine suitability, including wettability, chemical composition, and physicochemical stability.

ABSTRACT. Wood is a natural renewable resource and has been a common feature in stream stability across North America prior to extirpation of beaver, European colonization, and removal of wood from streams under the mistaken auspices of creating fish passage and mitigating flooding risks. Adding wood to riffle features to improve their habitat quality, using buried wood as bank stabilization and habitat improvement features, using rootwads to attenuate velocities and improve bank cover are all highly valued applications of wood in stream restoration. The use of wood in stream restoration structures is a logical refinement of stream restoration techniques. Building wood and earth plugs in incised, over-widened, and disconnected stream channels re-establishes lateral floodplain reconnection without extensive grading, creates deeper stream flow to support better aquatic life habitat and hyporheic connectivity,and reduces sediment and nutrient loading. In addition, this approach is regenerative and sustainable in a forested landscape. Wood production rates are higher than decomposition rates. Floodplain reconnection reduces in-stream shears and supports accumulation of wood and leaf material. The restored groundwater supports riparian and floodplain wetland community development and helps maintain stream temperature and flow during dry periods. Wood also creates a much more structurally complex habitat. A project totaling more than 20,000-lf that used engineered wood structures in combination with an understanding of natural stream and floodplain processes and functions to deliver significant functional uplift will be presented as a model for Gulf Coast stream restoration. The design approach, the regulatory experience, and the results of groundwater monitoring will be discussed. The goal is to stimulate more projects of this type by helping the design and construction community to build capacity for this type of truly sustainable ecological restoration.

ABSTRACT. Regulated rivers in urban areas control water levels for navigation, hydropower and recreation needs and at the same time avoid flooding. Consequently, the water level persists within a height range defining a shoreline based on the topographic characteristics along the river. This shoreline is consistent most of the year favoring accumulation of allochthonous materials such as leaves, stems, organic matter, sediments, among others. These allochthonous materials are broken down by biogeochemical processes, becoming an important source of greenhouse gas emissions. In this study we investigated the shoreline of a regulated river, the Kanawha River at the Central Appalachian Region, having a river shoreline defined by the historical readings of the river stage and identified by means of LIDAR maps. Then, samples from the river shoreline were incubated in the laboratory. Measurements of diffusive CO2 and CH4 fluxes were conducted finding emissions of (Mean±SE) 8729±879 and 340±76 µmol m-2 h-1 for CO2 and CH4 fluxes, respectively. With these fluxes, a river section of 58 km allowed us to estimate 61.02±6.51 and 0.91±0.21 kg/h for CO2 and CH4, respectively. Although, these estimations may have spatiotemporal variability due to atmospheric conditions such as temperature, it was possible to adjust these fluxes under a temperature-dependent estimation for a year. In this way, we overcome uncertainty from field conditions measuring CO2 and CH4 and also we suggest estimated annual fluxes.

ABSTRACT. This research aimed to quantify and compare the impact of two plant root mechanisms on streambank fluvial erosion using an 8 m long and 1 m wide flume channel. Plant roots can influence soil resistance to fluvial erosion through multiple mechanisms, including: 1) binding soil together through a thick root network and 2) interacting with soil microorganisms to stimulate the release of “sticky” organic compounds called extracellular polymeric substances (EPS). To study these mechanisms, soil treatments were created to represent unamended and organic matter (OM) amended soil either without roots (bare soil), with synthetic polyester/plastic fibers, or with living roots (Panicum virgatum). Dried and crushed grassed clippings (< 1 mm) were used as the OM additions. Erosion for each sample was tested using three different flow rates corresponding to mean channel speeds of approximately 0.3 m/s, 0.6 m/s, and 0.8 m/s.

Grass clippings stimulated the production of microbial EPS and appeared to increase the applied stress required to initiate soil erosion. Synthetic fibers alone provided a base reduction in soil erodibility by 30% to 72%, regardless of the flow rate used. When used in combination, synthetic fibers and the grass clippings reduced erosion rates by 86% to 100%; this reduction was identical to the live rooted treatments (95% to 100%) and statistically lower than the bare soil controls. In summary, these results highlight how the synergistic relationship between fibers and soil microbes can significantly reduce soil erodibility due to fiber reinforcement and “sticky” EPS production. While plant roots naturally provide both fibers and EPS to soils, these materials could be incorporated into fill soils during construction to rapidly increase soil erosion resistance following activities such as levee construction and stream restoration projects.

ABSTRACT. As impervious cover increases with development, increased stormwater runoff degrades stream channels which negatively impacts stream habitat quality and benthic macroinvertebrate assemblages. Watershed managers respond to urban stream degradation by repairing streams using restoration techniques; however, most natural channel design approaches do not achieve an uplift of benthic macroinvertebrate assemblages. To better understand the impact of urbanization on benthic macroinvertebrate assemblages, we conducted three studies that evaluated the impact of development from the watershed to the reach scale. We first looked at the impact of development, as measured by percent impervious cover, on stream habitat quality and benthic macroinvertebrate taxa and trait richness and diversity in 15 Piedmont stream in North Carolina over a 26-year period. We next evaluated the relationship between stream habitat quality and taxa and trait richness and diversity in 30 Piedmont streams spanning a gradient of good to poor habitat quality. We examined the distribution of taxa and traits among microhabitats. The third study examined the impact of stormwater on benthic macroinvertebrate taxa and trait richness and diversity by comparing two adjacent tributaries that received stormwater runoff via different processes: one from stormwater infrastructure draining a development and the other through more natural processes. The long term project identified thresholds of both % IC and stream habitat quality at which sensitive taxa and traits declined and thresholds at which tolerant taxa and associated traits increased in abundance. Taxa richness and diversity were positively correlated with stream habitat conditions while traits did change. Taxa and traits associated with specific microhabitats were identified. The stormwater study demonstrated that unmitigated stormwater can lead to both channel and stream habitat degradation which, in turn, negatively impacts the benthic macroinvertebrate assemblages. Incorporating these results into restoration design may improve the success in achieving biological uplift of an urban stream’s aquatic biota.

ABSTRACT. Millions of dollars are spent each year in North Carolina to remove debris (primarily large wood) from streams to reduce future flooding; however, aside from anecdotal observations, there has been little analysis or scientific documentation of the flood reduction benefits of these actions. There are also potential negative impacts of debris removal as large wood naturally supplied by the adjacent riparian buffer and upstream watershed sources is critical to stream and river habitat. In addition, many of the streams where debris removal is conducted have been substantially altered by human activities. The goal of this project was to quantify the flood reduction benefits of debris removal and to compare to other approaches including stream restoration. Three streams that were allocated funds for debris removal activities were selected for debris inventory and hydraulic modeling analysis. At each stream, channel cross sections were surveyed and the woody debris in the channels were inventoried along a 2500-foot reach. The survey cross sections and LiDAR data were used to develop 2D HEC-RAS models of each stream and several scenarios were evaluated: (1) existing condition with inventoried debris, (2) debris removed, and (3) 25%, 50% and 75% of the channel blocked by wood debris. Discharges corresponding to the 10-, 25-, 50-, and 100-year return periods were modeled. In addition to site specific modeling, a sensitivity analysis was conducted by varying the width of the floodplain, the stream channel slope and percent channel blockage in the hydraulic model. The impacts of debris removal across various storm return periods will be presented along with comparisons to the flood reduction benefits of stream restoration.

ABSTRACT. Stream erosion monitoring and assessment were conducted at 15 streams in the Blue Ridge and Ridge and Valley physiographic provinces of Virginia. Streambank erosion was measured at 82 cross sections and compared to erosion predictions estimated using the Bank Assessment for Non-point source Consequences of Sediment (BANCS) method. Several multivariate statistical models - Lasso, Ridge, PCR and Random Forest - were used to predict streambank retreat using the individual BANCs variables. Historical erosion rates were quantified for six streams using aerial photos taken in 2007, 2011, 2015 and 2019. LiDAR data was collected at 3 streams in 2021 and 2022. Geomorphic Change Detection (GCD) software was then used to calculate the reachwide erosion and deposition for each stream from this data. Streambank erosion volumes were calculated and compared at three streams using four approaches 1) physical surveys, 2) aerial photo analysis, and 3) LiDAR surveys and 4) model predictions. Total erosion volumes based on the physical surveys ranged from 0.01 to as high as 0.35 tons per year per linear foot of stream per year. The BANCS method overly stratified the data into Bank Erosion Hazard Index (BEHI) categories and as a result produced poor streambank erosion prediction curves. Four regression models provided more reliable predictions of streambank retreat than the BANCS model. The aerial imagery analysis and the physical stream surveys produced comparable total volumes of erosion. The GCD appeared to underestimate the volumes and included a higher range of uncertainty.

ABSTRACT. This presentation discusses a series of chamber incubations from two Southern Californian reservoirs, Lake Henshaw and Lake Wohlford, that examine the rate of nutrient flux from sediment and evaluate conditions favorable to internal nutrient loading. Lake Henshaw and Lake Wohlford are integral parts of the water supply for the City of Escondido, California and Vista Irrigation District. In recent years, harmful algal blooms and related algal toxins that degrade water quality and threaten the usability of the water sources have been detected in the reservoirs. Harmful algal blooms can be fed through a process known as internal nutrient loading, which is constituted by the release of ammonia, phosphate, and iron from the sediment. Episodes of low dissolved oxygen related to the decay of harmful algal blooms can exacerbate this internal nutrient loading. Within Lake Henshaw and Lake Wohlford chambers, anoxic conditions stimulated an increased flux of ammonia, phosphate, iron, and manganese from the sediment compared to oxic conditions in each reservoir, primarily as a result of organic matter decay coupled with repressed nitrification and reductive dissolutions of metal oxides. In Lake Henshaw chambers, hypoxic conditions resulted in a larger, positive flux of phosphate compared to oxic conditions. The flux of phosphate without a corelease of nitrogen lowers the N:P ratio and could impact algal communities and the lake ecosystem, suggesting that hypoxia may be an important oxygen condition in lake dynamics. The results of this study contribute directly to the greater understanding of internal loading in California reservoirs and inform management strategies to control harmful algal blooms and protecting water quality.

ABSTRACT. The Occoquan Reservoir in Northern VA is an indirect potable reuse system that during the last 50 years has used a nitrate rich effluent (nitrate > 14 mg-N/L) to improve the water quality of the reservoir during the summer months. The use of nitrate to keep an oxidized environment in freshwaters is not new. However, manipulating this application to enhance environmental processes in sediments seems like a promising sustainable nature-based solution to improve surface water quality. In the Occoquan, nitrate addition begins after the onset of thermal stratification in the reservoir. This study investigated the impacts of extending the nitrate addition practice outside the thermal stratification period to enhance simultaneous nitrification and denitrification at the sediment water interface (SWI). Microcosm studies simulating the reservoir revealed that nitrate depletion may occur when oxygen ranges between 0–4 mg/L above the SWI suggesting that DO concentration is not the only parameter controlling nitrate depletion in freshwater sediments. Results highlighted that other parameters such as oxygen depletion rate, sediment oxygen demand, and nitrate and organic matter availability are crucial in controlling denitrification. Specifically, denitrification in microcosms was significant when oxygen depletion was higher than 300 mg/m2·d and nitrate concentration was higher than 1 mg-N/L. Oxygen and nitrate profiles further revealed that denitrification occurred approximately 5 mm deep in the sediments despite high oxygen levels above the SWI (0–4 mg/L) demonstrating that denitrification, a strictly anaerobic reaction, is a continuous process in sediments layers having low oxygen. Field data also showed that conditions outside the period of thermal stratification were adequate to support denitrification in the reservoir. Results from this research can be used to improve models to better predict denitrification with the goal of identifying freshwater systems with ideal conditions to sustain nitrate removal though a nature-based alternative for nutrient reduction.

ABSTRACT. Freshwater harmful algal blooms (HABs) have become an increasing concern worldwide. Toxins associated with HABs pose health risks to humans and animals and subsequent closures of public waters negatively impact local economies. Increased frequency of climatic extremes and alterations to a variety of ecological conditions have intensified HABs and related problems in freshwater systems. In Kansas, surface water supply is heavily reliant on a network of man-made impoundments, or reservoirs. In addition to providing water supply, Kansas reservoirs provide flood management, maintain streamflow, and present recreational activities. Cyanobacteria HABs have been documented and monitored in several Kansas reservoirs, including Marion Reservoir. This research aims to better understand the environmental and ecological drivers of cyanobacteria in Marion Reservoir through monitoring and modeling approaches. Monitoring data collection includes discrete, spatially distributed water quality samples and continuous, in-lake monitoring with a multiparameter sensor. The collected monitoring data and supplemental environmental datasets will be utilized to inform modeling approaches. Overall, this project will aim to integrate modeling approaches including: a watershed model, lake model, cyanobacteria growth model, and data-driven models to characterize and provide a prediction framework for cyanobacteria harmful algal blooms. The capabilities of predicting cyanobacterial blooms would assist waterbody managers and monitoring programs by improving the response to blooms as well as provide a more detailed understanding of the dynamics, occurrence, and impact of cyanobacteria blooms in reservoir systems.

ABSTRACT. Reservoir operations can regulate nutrient fluxes that affect water quality of reservoirs themselves and receiving water bodies. I developed Lake Operation Optimization of Nutrient Exports (LOONE), a Python-based model that incorporates three coupled modules: 1) a water balance module to simulate water level and operations of a reservoir, 2) a water quality module to simulate dynamics of nutrients and Chlorophyll-a in the water column, and 3) an optimization tool to design optimal reservoir releases with the goal of reducing nutrient exports. The model is demonstrated for Lake Okeechobee in Florida, a large subtropical lake which receives and exports excessive amounts of nutrients, while providing water supply, recreation, and flood control for neighboring communities. LOONE was used to design optimal releases into main distributaries of the lake, St. Lucie Canal and Caloosahatchee River which could decrease P loads by 12-33%. This software package could be used by water managers and operators to evaluate different management strategies to help control water quality issues such as high nutrient exports and harmful algal blooms in reservoirs around the world.

ABSTRACT. Reduction of non-point source phosphorus runoff is an important priority of the Great Lakes Restoration Initiative (GLRI) and a key component of harmful algal bloom management in waterbodies like Lake Erie. As part of a U.S. Army Corps of Engineers-sponsored effort to reduce phosphorus loading from the Maumee River Watershed, a wetland demonstration site was constructed in Defiance, Ohio to treat runoff from Colwell Creek, a tributary in the Maumee River Watershed which drains around 900 acres of farmland. Water diverted from the creek first enters a settling pond and is then conveyed through four wetland cells via a pumping component and earthen berms, before being discharged back into the creek. The wetland site, a collaboration between USACE Buffalo District and ERDC-Environmental Laboratory, USGS, and LimnoTech, became fully operational in the Spring of 2022. Following wetland establishment, LimnoTech installed water level sensors, water quality sondes, online nutrient analyzers, and automated ISCO samplers to provide insights into the wetland’s function and performance regarding phosphorus retention. Preliminary results from four rain events across May and June 2022 suggest a lag time of ~12 hours or more between inflow and outflow peaks. Turbidity results indicate the system is effective at reducing suspended particulates, and therefore particulate phosphorus. Preliminary dissolved phosphorus concentration results suggest that dissolved P is also being effectively reduced as dissolved P concentrations decreased between the wetland inlet and outlet by greater than 50% throughout the Spring 2022 observation period. The site experienced incremental reductions in phosphorus concentrations throughout the wetland, with the highest reductions occurring within the settling basin and first wetland cell.

ABSTRACT. Water quality is an essential factor for the effective management of ecological systems. Water quality is typically defined by concentrations of various ecologically relevant parameters such as chemical species containing carbon, nitrogen, and phosphorus. There is a multitude of methods for measuring water quality, each having its own advantages and disadvantages in terms of a variety of factors such as accuracy, technical difficulty, instrumental requirements, cost, and usefulness. Hydrochemical analysis using Ultraviolet-visible absorption spectroscopy and Machine learning (HUM) is a water quality methodology that has been developing in recent years. One of the main benefits of this methodology is that a single instrumental setup can be used to measure the concentration of multiple water quality parameters. However, commercially available instruments designed for performing this method are costly, difficult to work with, and limited in their capacity to be tuned for measuring a specific set of water quality parameters and to incorporate this information into automatic decision-making frameworks. Research is currently being performed to address some of these limitations with the vision of someday producing a technology that can be easily incorporated into ecologically engineered systems. In the future, this technology could be used in applications such as real-time control of stormwater systems, automated agricultural nutrient management, and high-frequency monitoring of watershed processes. The goal of this presentation is to provide a conceptual overview of the HUM technology, describe current research being performed at the University of Florida, and discuss this information in terms of ecological systems management.

ABSTRACT. Pesticide applications are a necessary part to increasing agricultural production for the growing world population, but bulk pesticide application has resulted in environmental contamination, human toxicity, and endangerment to non-target species (e.g. honeybees, monarch butterflies). Engineered nanoparticles (ENP) are a potential solution with increased efficiency, longer duration, and enhanced stability of pesticides. However, their potential long-term impact to agroecosystems is still unknown. Therefore, the goal of this project was to evaluate the fate, transport, and persistence of two nanopesticides (copper(II) hydroxide and nano-imidacloprid) within soils and runoff water of agricultural systems in Central Kentucky. It was hypothesized nanopesticides would remain in the soil, with the formation of toxic byproducts occurring from interactions between the soil and/or sunlight, which are then transported by surface runoff. The study was completed using field scale applications of the pesticides on thirty 2.4 m by 6.1 m plots enclosed with metal boundaries. Surface water and soil samples were collected following rainfall events and throughout the growing season. Samples were analyzed for nutrients, pesticide, and pesticide byproducts along with physiochemical soil/water characteristics (e.g. pH, specific conductivity, temperature). Preliminary results indicate these pesticides did not have a significant impact on nutrient transport leaving the systems throughout the entire growing season. Further, findings related to pesticide transformation and fate and transport will provide guidance for nanopesticide regulation and application standards to prevent ecological disasters.

ABSTRACT. Excess phosphorus (P) in agriculturally dominated watersheds can lead to water quality issues and eutrophication in downstream waters. Lake Champlain, located along the borders of New York, Vermont, and Quebec, has been impacted by excess nutrient loading from its watershed and is under a Total Maximum Daily Load (TMDL) for phosphorus. Restoration of riparian wetlands is one method frequently proposed for storing P to reduce downstream flux to receiving waters. Wetlands commonly serve as nutrient sinks, however the P retention benefits of riparian wetlands restored on formerly farmed land are more uncertain than for other wetland types. To determine P flux regimes under different inundation conditions and at varying times since restoration, we monitored water quality during flood events at five restored, riparian wetlands on former agricultural lands in two sub-watersheds of the Lake Champlain Basin in Vermont. Surface water samples were collected, and temperature, dissolved oxygen, and pH were recorded at plots across the wetlands and in rivers adjacent to the sites during the rising and falling limbs of flood events. Water samples were analyzed for soluble reactive P, total P, and total suspended solids (TSS). Pressure transducers installed at low elevation plots at each site were used to monitor inundation frequency and duration. Additionally, soil core incubation experiments were conducted to quantify the potential for soluble reactive P release in inundated wetlands under aerobic and anaerobic conditions. Water quality trends across seasons, and under variable inundation frequency and duration, help clarify key factors that can influence P retention in these ecosystems. Our findings can inform wetland restoration design and nutrient management efforts.

ABSTRACT. The 4Rs of nutrient stewardship - Right Source, Right Rate, Right Time, Right Place - are essential for properly managing, applying, and keeping nutrients on agricultural fields. Research has shown that water quality is directly impacted by in-field management decisions meaning these decisions are important for both reducing agronomic inputs and minimizing the nutrient loss through tile and surface runoff. The Right Rate component of the 4Rs is informed primarily from soil nutrient concentrations taken from discrete areas within a field. Fields are commonly sampled either by grids or zones of 4-8 – acres in size, distinguished by factors such as soil type, management history, and/or yields. Headlands (also known as end rows along field boundaries) are rarely represented in these sample zones because of their small areas and assumed nutrient differences from compaction, yield drag, etc. By partnering with an agricultural retailer who samples these headlands soils as distinct zones, we have analyzed nutrient concentrations from over 220 fields representing over 10,000 acres in Northwest Ohio. We found that Soil Test Phosphorus concentrations are 30% higher in the headlands compared to in-field zones while other nutrients varied by less than 10%. This presentation will summarize these findings while also exploring the temporal component of these nutrient concentrations by studying those headlands which have been sampled a minimum of three times, spanning, approximately nine years.

ABSTRACT. Controlled environment agriculture (CEA) has potential to revolutionize food production through increased productivity and quality of products. The high technology and high level of control in CEA establishes an approach for high levels of production of many desirable and valuable agricultural products. Particular implementations, such as many aquaponics and paired aquaculture-horticulture production systems, employ controlled nutrient chemical environments along with controlled physical environments that promise high productivity of cultivated crops. Systems of this sort are designed around closed nutrient cycles, employ diverse microbial ecosystems, and support higher order species for valuable crops, and in that way approach a constructed and designed ecosystem. State of the field, however, employs little ecological design know-how, and often diverges far from most ecotechonologies because of the high proportion of technology necessary for containment and control. In this talk, the state of CEA and aquaponics approaches will be critically reviewed, and components of ecological engineering applied to these systems will be discussed for assessment of CEA as a future sustainable food production strategy.

ABSTRACT. In freshwater systems like Lake Erie, agricultural sources of phosphorus drive harmful algal blooms, jeopardizing drinking water and aquatic habitats. To reduce agricultural phosphorus losses, phosphorus removal structures (PRSs) have been implemented as a phosphorus-sorbing buffer between agricultural production and aquatic ecosystems. These structures can contain manufactured media like slag or activated alumina, which create chemical bonds between the phosphorus and media, decreasing the dissolved phosphorus load downstream. As legacy phosphorus agricultural sources continue to prevent the Lake Erie watershed from reaching its phosphorus loading goals, it is necessary to target potent conservation practices to these critical sources of phosphorus. While PRSs have been effective at reducing surface sources of phosphorus, there have not been many field-scale studies at tile-drained settings. To fill this gap in knowledge, we evaluated two PRSs with novel phosphorus sorbing media to examine how their performance changes over their lifetime. Preliminary data are presented on how phosphorus sorption is affected by sediment and chemical clogging and efficacy changes based on the size of precipitation events. The performance of this technology would likely benefit from being paired with a practice that reduces peak water flow and sediment losses, like a constructed wetland.

ABSTRACT. In 2011, the Florida Department of Environmental Protection (FDEP) established a 0.35 milligrams per liter (mg/L) nitrate+nitrite-nitrogen (NOX-N) numeric nutrient criterion for springs. In 2018, the FDEP finalized the Santa Fe River Basin Management Action Plan (BMAP) requiring wastewater facilities over 0.1 million gallons per day (MGD) to achieve the advanced wastewater treatment (AWT) standard for total nitrogen (TN) of 3 mg/L as an annual average concentration. The FDEP assumes that natural attenuation of applied reclaimed water with no more than 3 mg/L of TN will also meet the NOX-N standard at spring vents.

The Santa Fe River Basin largely consists of small, rural communities that cannot fund the conventional wastewater treatment upgrades needed to meet the TN standard. These communities have instead considered alternative treatment methods to achieve nitrogen removal to meet AWT. The City of Lake City constructed 120 acres of recharge wetlands in 2016 to meet the BMAP requirements for about 1.5 MGD of their reclaimed water and are proceeding with the design and construction of additional recharge wetlands to fully meet their obligations. These wetlands are constructed above a thick, but discontinuous clay layer that overlays the Floridan Aquifer. To date, the initial Lake City project has removed over 120,000 pounds of nitrogen and recharges the aquifer with TN and NOX-N concentrations below their respective standards. The City of High Springs has permitted and will construct 20 acres of treatment wetlands to comply with their BMAP nitrogen reduction requirements. The geology at High Springs consists of highly permeable sands directly over the aquifer, so lined cells will be constructed to meet the 3 mg/L TN standard before aquifer recharge occurs in unlined recharge wetland cells. These wetland projects have proven to be cost-effective and beneficial AWT alternatives for rural communities.

ABSTRACT. Subsurface gravel wetlands (SGW) are water treatment practices that use a saturated layer of gravel, sometimes below a vegetated soil layer, to filter urban stormwater and remove pollutants during horizontal flow. In recent years, the implementation of SGWs has proliferated among municipalities in the Northeast United States to meet phosphorus (P) control requirements. However, stormwater SGW performance is not well researched, creating knowledge gaps related to P removal performance and the effects of road salt on performance in cold climates. Here, we used field monitoring of two SGWs over two years and a complementary series of laboratory studies to examine SGW hydraulics, P retention, and chloride dynamics. Field results indicated reductions in peak flows and flow volumes, net P export for approximately half of the total storms monitored across a wide range of influent P loads, and chloride load reductions at one site. Lab results showed that both engineered soils and native soils are unlikely to restrict hydraulic conductivity to the degree desired. Furthermore, two out of three engineered soils tested, including the one used at the field sites, can release substantial P post-installation, while gravels have limited ability to sorb dissolved P. Neither soils nor gravels substantially influenced chloride concentrations in the lab experiments, and results illustrated two potential responses of wetland vegetation to chloride exposure in SGWs as well as chloride assimilation by vegetation. We make recommendations to improve SGW performance for urban stormwater treatment in cold climates, including a testing protocol to guide soil selection.

ABSTRACT. Sweetwater Wetlands Park is a nutrient reduction and environmental restoration located at the interface between the Gainesville urban area and Paynes Prairie Preserve State Park. The project receives stormwater runoff, industrial discharges and wastewater effluent from a 2,100-acre watershed that is 80% urbanized. The project removes nutrients, trash and sediment to produce a high quality water that is used to restore the natural flow pattern to wetlands within the state park.

Stormwater runoff, industrial discharges, effluent from the Main Street Water Reclamation Facility (MSWRF), and discharges from septic systems in the watershed flow into Sweetwater Branch, an urban stream that was historically channelized. Prior to the project nutrients, sediment and trash were conveyed directly to Paynes Prairie via a manmade channel which, allowed the direct discharge of these combined flows to the Floridan Aquifer at Alachua Sink, which is an impaired water body located within Paynes Prairie Preserve State Park.

The Project includes the following: • MSWRF upgrade for phosphorus removal, • Sweetwater Branch channel improvements to stabilize the channel, capture sediment and trash, • Creation of a 125-acre treatment wetland to provide a unique and innovative approach to achieving TMDL requirements, • Construction of a 1.25-mile long sheetflow distribution channel, and • Backfill over 1 mile of existing canal to eliminate short circuiting.

Long-term water quality monitoring demonstrates Project performance with the following criteria: • Rolling 5-year average of Total Nitrogen (TN) in the discharge from the proposed system is equal to or less than 3 milligrams per liter (mg/L); and • Rolling 5-year average of Total Phosphorus (TP) in the discharge of the proposed system is equal to or less than 0.3 milligrams per liter (mg/L).

This presentation summarizes performance monitoring data collected during the first six full calendar years of operation (January 2016 – December 2021).

ABSTRACT. Declining performance in free water surface constructed wetlands (FWS CW) can often have a hidden cause - the accretion of decaying biomass, or detritus. Over time (10-20 years), this detritus can form a thick layer sometimes 30 cm or more above the original wetland soil elevation. As FWS CWs continue to age across the country, we need to better understand the influence of this accumulated detritus substrate on nitrogen (N) treatment to inform operators about the importance of management and removal. A laboratory study was conducted to quantify the ammonium (NH4-N) released from layers of detritus and to develop a kinetic model that would represent this release. In this study, three experimental runs were conducted, each using nine wetland microcosms loaded with detritus (mainly from Typha spp.) from a 20+ year old FWS CW that has declined in N removal performance. Each run was conducted with three variable initial NH4-N concentrations in the water column (0 mg L-1, 5 mg L-1, and 10 mg L-1). The release NH4-N release was reasonably represented using first order kinetics (mean R2 = 0.77). Valid parameter values were calibrated for 23 of the 27 wetland microcosms. The potential areal ammonium release rates (JUF) from the detritus substrate at an overlying water column concentration of 4 and 6 mg L-1 were 0.21 and 0.14 g-N m-2 d-1 (70 and 50 g-N m-2 yr-1), respectively. At these rates, NH4-N diffusion from the detritus substrate would substantially reduce N removal performance in lightly loaded systems (TKN load < 120 g-N m-2 yr-1). These results provide both an initial estimate of the magnitude of N release from an accumulated detritus substrate and further evidence to support regular FWS CW maintenance through detritus removal.

ABSTRACT. It is estimated that in 1900 there were approximately 20 million acres of freshwater wetlands in Florida. Recent estimates suggest that only 8 million acres remain. During that time population has increased by almost 22 million people. Exacerbated by climate change, Florida suffers from water shortages, flooding, and water quality driven ecological disasters. New approaches to water management are desperately needed, and wetlands technology is among the most promising solution. Beginning with the work of H.T. Otum and the establishment of the University of Florida Center for Wetlands, Florida has pioneered the use of wetlands for water management. The nations’ first large-scale constructed wetlands for wastewater and stormwater were implemented in Florida starting in the 1980’s and many continue to operate today. More recently, driven by onerous regulatory requirements and a desire to provide sustainable water management solutions, dozens of treatment wetland projects have been implemented throughout the state. Examples include the popular Wakodahatchee Wetlands and Green Cay Wetlands in Palm Beach County, the Sweetwater Wetlands in Gainesville, the 4G Ranch Wetlands in Pasco County, and the Wetland Recharge Park in Ocala. Treatment wetland design is supported by more performance data than ever before. Design principles have evolved through the decades and focus on more precise project goals such as water supply augmentation, TMDL driven load reductions, and water quality based effluent limits. Today, the use of natural wetlands for wastewater effluent management, the implementation of infiltration wetlands, and the more traditional flow-through wetlands have more complex and better-defined success metrics. This presentation will provide a history of treatment wetland technology in Florida, it will highlight key projects that led to the growth of the technology and will identify the future challenges that will drive the next generation of wetland projects and practitioners.

ABSTRACT. Constructed wetlands (CWs) represent a natural wastewater treatment process, offering economic and environmental advantages. These systems can remove several compounds that may cause negative impacts on the environment while reducing peak flows and enhancing ecosystem services. On the other hand, anaerobic membrane bioreactor (AnMBR) is an innovative technology combining biological treatment and membranes for solid-liquid separation. The AnMBR is effective to transform organic compounds into biogas while creating permeate rich in nutrients (ammonia-N and phosphate-P). The combination of these two technologies can generate a high-quality effluent, meeting superior discharge standards. Thus, the goal of this study is to evaluate the capacity of an AnMBR coupled with CWs to remove contaminants from swine wastewater. The CWs were designed to operate with a 10 cm drainage layer (gravel size ¾” to 1”), a 20 cm main gravel layer (gravel size ½” to ¾”), a 3 cm separation layer (gravel ¼” to 3/8”), a 20 cm layer of soil (silt loam:sand, 2:1 ratio) mixed with eastern redcedar biochar (70% soil and 30 % biochar), and 7 cm top layer (gravel size ½” to ¾”). The systems were planted with cattail, a low cost and low maintenance plant often used for biomass production and is able to tolerate cold weather and occasional flooding. Results indicate that the CWs are effective to remove up to 99.5% of NH4+ and P from the AnMBR effluent. Moreover, sorption tests show that the biochar used in the CW configuration was able to decrease the concentrations of commonly used antibiotics in the swine industry such as tetracycline, oxytetracycline, and chlortetracycline up to 99.93%, 96.23%, and 98.28%, respectively. Thus, our findings highlighted the capacity of this CWs design to be used as a polishing step for AnMBR, while removing antibiotics and generating an effluent with nutrient concentrations below 1 mgL-1.