SFS Annual Meeting

6/04/2024  |   13:30 - 13:45   |  Independence Ballroom C

Environmental Controls on Nitrogen Cycling along a Salinity and Urbanization Gradient Eutrophication caused by excess nitrogen impacts estuaries worldwide. To prevent eutrophication, management agencies develop plans to reduce nitrogen loads from land. Yet, mandated nitrogen reductions alone are often not enough. At the transitional zone between freshwater and saltwater, estuaries process and remove reactive nitrogen through denitrification. However, denitrification is variable in space and time, making it difficult to predict and integrate into watershed nitrogen budgets. The Guana Estuary in northeast Florida has a gradient of human influence and suffers from excess nitrogen with regular algal blooms. Nutrient-rich freshwater enters through a single point in the upper estuary. In the lower estuary, salt marshes and shellfish beds process and remove reactive nitrogen through denitrification. We measured rates of sediment nitrogen cycling processes and planktonic responses, including denitrification and phytoplankton nutrient limitation, over an annual cycle from the headwaters to the mouth of the Guana Estuary. Denitrification (net N2 production) varied spatially and temporally within the estuary, with extreme nitrogen fixation rates (net N2 consumption) in the summer months. The upper estuary had a strong affinity for nitrogen, as evidenced by increased phytoplankton biomass and sediment demand when reactive nitrogen was available. Within the lower estuary, shellfish presence, particularly mussels, increased salt marsh denitrification, highlighting the role of filter feeders in estuarine nitrogen cycling. While there was no clear pattern with salinity, this research can help improve nitrogen budgets, quantify ecosystem services, and aid in developing water quality restoration plans for the urbanizing Guana Estuary.

Ashley Smyth (Primary Presenter/Author), University of Florida, ashley.smyth@ufl.edu;

Justina Dacey (Co-Presenter/Co-Author), University of Florida, jdacey@ufl.edu;

Hallie Fischman (Co-Presenter/Co-Author), University of Florida, halliefischman@ufl.edu;

Jenna Reimer (Co-Presenter/Co-Author), University of Florida, reimerj@ufl.edu;

Alexander Reisinger (Co-Presenter/Co-Author), University of Florida, reisingera@ufl.edu;

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6/04/2024  |   13:45 - 14:00   |  Independence Ballroom C

A Collaborative Science Approach To Adaptive Management Of Nitrogen Pollution And Eelgrass Health In Great Bay Estuary, NH/ME Great Bay Estuary, NH/ME, is designated as nitrogen impaired due to significant eelgrass habitat loss over the last two decades. High nitrogen loading from both point and non-point sources throughout the watershed, combined with eelgrass decline, led to the release of a regulatory general nitrogen permit. The permit focuses on reducing nitrogen loads from 13 out of 17 wastewater treatment facilities (WWTF) in the watershed, while also offering adaptive management options for non-point nitrogen sources. Recent upgrades to municipal WWTFs resulted in a 64% decrease in point source nitrogen loading between 2012 and 2020. As the general permit is up for renewal in 2025, a collaborative science project has sought to better understand the relationships between nitrogen loading, water quality, hydrodynamics, and eelgrass health to directly inform adaptive management of Great Bay Estuary. We leveraged two spatial scales of monitoring, including site level monitoring of 25 eelgrass meadows and three transects that span a habitat gradient of subtidal mudflat to eelgrass meadows. Water chemistry samples, eelgrass and seaweed metrics, and hydrodynamic estimates of water residence time and water parcel history, have been combined to paint an ecosystem-wide perspective of nitrogen cycling in Great Bay Estuary. Over a three-year period, we have worked closely with municipal stakeholders to explore the spatial variability in eelgrass response to changing water quality and to quantify the ecosystem services (e.g. nutrient cycling, sediment attenuation) provided by the remaining eelgrass meadows in Great Bay Estuary.

Anna Mikulis (Primary Presenter/Author), University of New Hampshire, Anna.Mikulis@unh.edu;

David Burdick (Co-Presenter/Co-Author), University of New Hampshire, David.Burdick@unh.edu;

Kalle Matso (Co-Presenter/Co-Author), Piscataqua Region Estuaries Partnership, Kalle.Matso@unh.edu;

Tom Lippmann (Co-Presenter/Co-Author), University of New Hampshire, lippmann@ccom.unh.edu;

William H McDowell (Co-Presenter/Co-Author), University of New Hampshire, bill.mcdowell@unh.edu;

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6/04/2024  |   14:00 - 14:15   |  Independence Ballroom C

Ecosystem Change Following Disappearance of Submersed Aquatic Vegetation from an Embayment of the Tidal Freshwater Potomac River. For 10 years a suite of water quality and biological parameters was measured in Hunting Creek, a shallow embayment of the tidal Potomac River just downstream from the District of Columbia. The system had a robust community of submersed aquatic macrophytes dating from the 1990’s which helped to structure the ecosystem and create what has been called a “clear water” system with high light transparency and minimal phytoplankton growth. In 2013 we initiated a long-term ecosystem study in which we documented this clear water system for five years. Zooplankton were abundant and the dominant fish was Banded Killifish. In 2018, high summer rainfall and resulting runoff, particularly from the immediate watershed resulted in very low transparencies all summer and probably washed away some of the plants. This was followed by another high runoff year in 2019. The result was the complete disappearance of aquatic macrophytes from the system for the remaining five years of the study (2018-2022). A major change was observed in the ecosystem. Secchi depths dropped from about 0.8 to 0.45 m, total suspended solids rose from about 10 to about 30 mg/L, and chlorophyll a doubled. Many zooplankton taxa dropped in abundance and White Perch assumed dominance in fish collections. Despite several years of near normal flows without flushing events, aquatic macrophytes have been unable to recolonize and the “turbid water” stage is persisting.

R Christian Jones (Primary Presenter/Author), George Mason University, rcjones@gmu.edu;

T Reid Nelson (Co-Presenter/Co-Author), George Mason University, tnelso3@gmu.edu;

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6/04/2024  |   14:15 - 14:30   |  Independence Ballroom C

WATER COLUMN BIOASSAYS AND N2 FLUXES SUGGEST N LIMITATION IN AN URBAN RIVER AND ADJACENT STORMWATER PONDS Stormwater ponds (SWPs) are constructed to retain stormwater and slow its discharge into nearby streams and rivers, offsetting urban stream syndrome. Stormwater entering SWPs often contains elevated concentrations of nutrients which can be retained or removed by heterotrophic and autotrophic microbially mediated processes. When SWPs overflow, water is discharged to natural streams and rivers, transporting microbial communities and excess nutrients. To understand the impact of SWP effluent on biogeochemical dynamics within an urban river, we quantified rates of planktonic nutrient uptake (via nutrient addition cubitainer bioassays) and net N2 flux (denitrification vs. N fixation measured via changes in N2) along a river continuum in a SWP-dense region in Bradenton, FL. Water for incubations was collected from a headwater and downstream site and two adjacent SWPs during wet and dry seasons. Bioassay treatments included additions of nitrate (NO3-), ammonium (NH4+), phosphate (PO43-), and a control (no addition). Rates ranged from -0.11 (nutrient removal) to 0.025 (nutrient generation) mg NO3-/L/hr, -0.020 to 0.019 mg NH4+/L/hr, and -0.041 to 0.028 mg PO43-/L/hr. Both NH4+ and PO43- uptake differed between seasons and sites (p < 0.05), NO3- uptake did not differ between site, season, and treatment. Net N2 incubations revealed that sites were typically N-fixing (indicating nitrogen limitation), ranging from -39 (net N-fixation; SWP) to 3.7 ?g N2-N L-1 hr-1 (net denitrification; headwater stream). These results suggest that uptake rates are largely site dependent, N-limitation may be similar across sites, and there may be other factors that determine microbial nutrient uptake.

Annabel Schreiber (Primary Presenter/Author), University of Florida, annabel.schreiber2@gmail.com;

Audrey Goeckner (Co-Presenter/Co-Author), University of Florida, agoeckner@ufl.edu;

Alexander Reisinger (Co-Presenter/Co-Author), University of Florida, reisingera@ufl.edu;

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6/04/2024  |   14:30 - 14:45   |  Independence Ballroom C

DISSIMILATORY NITRATE REDUCTION TO AMMONIUM (DNRA) CAN UNDERMINE NITROGEN REMOVAL EFFECTIVENESS OF PERSISTENTLY HYPOXIC RIPARIAN SEDIMENTS UPSTREAM OF MILLDAMS Milldams alter riparian hydrology and redox conditions and may also affect riparian nitrogen (N) processing. Denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) compete in hypoxic sediments where DNF permanently removes N while DNRA retains N with the conversion of nitrate (NO3-) to ammonium. We investigated the relative magnitude and controls of these two processes at two milldam-affected riparian sites. DNRA accounted for 10-79% of total nitrate (NO3-) reduction and was highest in riparian sediments with higher iron (Fe) and sodium (Na+) in riparian groundwater. DNF was the primary mechanism for NO3- reduction when Fe and Na+ concentrations were low but NO3- was relatively high. DNRA rates were higher for treatments with elevated dissolved organic carbon (DOC) to NO3- and Fe:NO3- ratios, indicating the stimulation of both heterotrophic and Fe2+ driven autotrophic DNRA. DNF and DNRA rates and their microbial functional genes decreased with increasing sediment depths. These findings imply that persistently hypoxic and stagnant conditions associated with relict milldams may enhance DNRA at the expense of DNF and thus undermine permanent N removal in riparian zones. Thus, the effects of milldams need to be accounted for in watershed N budgets and management strategies.

Md Moklesur RAHMAN (Primary Presenter/Author), University of Delaware, mmrahman@udel.edu;

Marc Peipoch (Co-Presenter/Co-Author), Stroud Water Research Center, mpeipoch@stroudcenter.org;

Jinjun Kan (Co-Presenter/Co-Author), Stroud Water Research Center, jkan@stroudcenter.org;

Matthew Sena (Co-Presenter/Co-Author), University of Delaware, senam@udel.edu;

Bisesh Joshi (Co-Presenter/Co-Author), University of Delaware, bjoshi@udel.edu;

Dipankar Dwivedi (Co-Presenter/Co-Author), Lawrence Berkeley National Laboratory, ddwivedi@lbl.gov;

Arthur Gold (Co-Presenter/Co-Author), University of Rhode Island, agold@uri.edu;

Peter Groffman (Co-Presenter/Co-Author), City University of New York, Peter.Groffman@asrc.cuny.edu ;

Shreeram Inamdar (Co-Presenter/Co-Author), University of Delaware, inamdar@udel.edu;

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6/04/2024  |   14:45 - 15:00   |  Independence Ballroom C

Tracking downstream water quality benefits of urban stream restoration using high spatial- resolution longitudinal monitoring Urbanization and impervious surface cover contribute to increased nonpoint sources of pollution in stormwater runoff. Additionally, urban streams suffer from streambank erosion and hydrologic disconnection, further degrading water quality. Stream restoration is considered a best management practice (BMPs) frequently implemented to mitigate the impacts of urbanization, reduce pollutant concentrations, and improve stream health. Under many federal programs and restoration plans, it is presumed that the benefits of localized stream restoration propagate downstream, however there is little research to validate this assumption. To better understand if and how stream restoration improves water quality both locally and downstream of restoration activities, we sampled Paint Branch Creek, an urban stream in Maryland, USA, monthly using high spatial resolution longitudinal synoptic monitoring. We focused monitoring efforts around two restored stream reaches, sampling directly above and 0, 100, and 200 meters below each restored reach to characterize how far downstream the water quality benefits of various restoration activities propagate. Results suggest that stream restoration can cause observable decreases in the concentrations of several contaminants of concern, with water quality improvements persisting up to 200 meters downstream of restoration activities. Additionally, longitudinal synoptic monitoring revealed the ability of urban land use features to either act as sources or sinks for contaminant loading. Improving our understanding of the efficacy and benefits of stream restoration activities will allow stakeholders to better design, select, and implement restoration activities to maximize pollutant load reductions on watershed scales.

Steven Hohman (Primary Presenter/Author), Environmental Protection Agency , hohman.steven@epa.gov;

Paul Mayer (Co-Presenter/Co-Author), United States Environmental Protection Agency, mayer.paul@epa.gov;

Sujay Kaushal (Co-Presenter/Co-Author), University of Maryland, skaushal@umd.edu;

Maria Morresi (Co-Presenter/Co-Author), Environmental Protection Agency, morresi.maria@epa.gov ;

Ruth Shatkay (Co-Presenter/Co-Author), University of Maryland, rshatkay@terpmail.umd.edu;

Matthew Frank (Co-Presenter/Co-Author), Environmental Protection Agency, frank.Matthew@epa.gov;

Kristopher Denardi (Co-Presenter/Co-Author), Environmental Protection Agency, denardi.kristopher@epa.gov;

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