5/18/2015  |   10:30 - 10:45   |  102C

FRESHWATER MUSSELS INCREASE SEDIMENT DENITRIFICATION IN AN URBAN RIVER Freshwater mussel (Unionidae) beds are biogeochemical ‘hotspots’ in lotic ecosystems. Other bivalves with dense colonies (e.g., zebra mussels, Asian clam, oysters) enhance conditions required for denitrification, or the anaerobic reduction of nitrate to nitrogen gas, a loss of nitrogen (N) from the aquatic environment. Unionid’s role in denitrification is unknown. In summer 2014, we measured density, assimilation, and sediment N cycling effects of Lasmigona complanata (white heelsplitter) and Pyganodon gradis (giant floater) in the DuPage River’s East Branch near Chicago, Illinois, USA. We completed streamside measurements of feeding and biodeposition, and flow-through mesocosms with 15N tracers (as ammonium and nitrate separately) with live mussels in the laboratory. Both taxa significantly increased nitrate uptake and denitrification relative to sediment alone. Feeding rates were similar between mussel species, however, N biodeposition was greater in L. complanata. We calculated the economic value of mussel-mediated denitrification as an ecosystem service using well-established methods for oysters. Overall, freshwater mussels enhanced denitrification despite eutrophic conditions, and their contribution to N removal as an ecosystem service may represent an underutilized conservation tool for this widely imperiled taxon.

Timothy Hoellein (Primary Presenter/Author), Loyola University Chicago, thoellein@luc.edu;
Dr. Hoellein is a freshwater ecologist at Loyola University Chicago. His research interests are focused on ecosystem processes and biogeochemistry. His research lab explores these areas in associate with the movement and biological transformation of elements, energy, and pollution in aquatic ecosystems.

Chester Zarnoch (Co-Presenter/Co-Author), Baruch College, City University of New York, Chester.Zarnoch@baruch.cuny.edu;


Denise Bruesewitz (Co-Presenter/Co-Author), Colby College, dabruese@colby.edu;

5/18/2015  |   10:45 - 11:00   |  102C

SEASONAL DENITIRFICATION AND NITROGEN REMOVAL CAPACITY OF SMALL RESERVOIRS Research has shown that aquatic ecosystems with high hydraulic residence times (e.g., wetlands and reservoirs) can be important nitrogen sinks via denitrification. The objective of this study was to examine denitrification rates and the nitrogen removal capacity each month in three small to mid-sized reservoirs (Jordan Pond, Springville Pond, and McDill Pond) in central Wisconsin between May and September of 2014. A two-way ANOVA determined that Jordan and Springville Ponds had significantly higher denitrification rates (4.97 and 4.59 mg N m-2 hr-1, respectively) than McDill Pond (2.71 mg N m-2 hr-1). In addition, Springville Pond had the highest hydraulic residence time (6.8 days) but surprisingly it had the lowest nitrogen removal capacity (3.5%) compared to Jordan Pond (10.3%) and McDill Pond (9.6%). We determined that nitrogen removal via denitrification was insignificant in Springville Pond due to the high incoming nitrate concentration (7.9 mg N L-1). Results from this study suggest that reservoirs in central Wisconsin can become nitrate saturated and in such cases appear to remove significantly lower amounts of nitrate than predicted.

Bree Richardson (Primary Presenter/Author), Kent State University, bricha34@kent.edu;


Kyle Herrman (Co-Presenter/Co-Author), University of Wisconsin - Stevens Point, kyle.herrman@uwsp.edu;

5/18/2015  |   11:00 - 11:15   |  102C

ENVIRONMENTAL DRIVERS OF DENITRIFICATION IN NORTH CAROLINA STREAMS AND RIPARIAN ZONES Agricultural land use practices adversely impact streams resulting in channelization, erosion, and sedimentation, while excess nitrogen (N) from agricultural runoff can cause eutrophication, algal blooms, and widespread anoxia in water systems. Though in-stream restoration strategies are often designed to reduce stream bank erosion, they may have the added benefit of improving water quality through denitrification. This study measured denitrification enzyme activity (DEA) across the riparian-to-stream continuum in distinct geomorphic features. This work was conducted in restored and unrestored stream reaches in two agricultural catchments of the Piedmont region of North Carolina. Potential environmental drivers of denitrification (e.g., water chemistry, organic content of soils, soil moisture) were also determined. Across all sites, DEA was significantly higher in the riparian zone than in the stream (p < 0.001), while dormant season DEA was significantly higher than growing season DEA (p < 0.001). Our results highlight the importance of soil texture in stream sediments and percent moisture and organic carbon in the riparian zone in controlling DEA. This study also illustrates the importance of stream-floodplain connectivity and riparian buffers in improving water quality.

Molly Welsh (Primary Presenter/Author), The State University of New York College of Environmental Science and Forestry, mkwelsh@syr.edu;


Sara McMillan (Co-Presenter/Co-Author), Iowa State University, swmcmill@iastate.edu;


Philippe Vidon (Co-Presenter/Co-Author), The State University of New York College of Environmental Science and Forestry, pgvidon@esf.edu;

5/18/2015  |   11:15 - 11:30   |  102C

QUANTIFYING THE EFFECTS OF ENVIRONMENTAL VARIABLES ON THE COMPOSITION AND ACTIVITY OF DENITRIFYING MICROBIAL COMMUNITIES Denitrification hot spots, or small areas of enhanced denitrification activity, frequently account for a high percentage of overall denitrification in streams and floodplains. This research aims to identify and quantify parameters that enhance denitrification hot spots. Investigated parameters include the influence of carbon type and concentration, flow characteristics, and flooding frequency and duration. This research is of significance in the upper Midwest due to the elevated nitrate concentrations in agricultural regions, which causes degradation of water quality and health concerns. Results will be presented from flume, field, and a controllable outdoor experimental stream experiments. The denitrification potential of each sediment sample was determined using the denitrification enzyme activity (DEA) assay and the abundance of denitrifying genes was quantified using qPCR. Integrating the denitrification potential with the quantity of denitrifying genes provides insight into the effect of environmental variables on both the composition and activity of microbial communities and provides a microbial processed based understanding for sustainable surface water management to promote denitrification.

Abigail Tomasek (Primary Presenter/Author), St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, toma0074@umn.edu;


Miki Hondzo (Co-Presenter/Co-Author), St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, mhondzo@umn.edu;


Jessica Kozarek (Co-Presenter/Co-Author), St. Anthony Falls Laboratory, University of Minnesota, jkozarek@umn.edu;


Michael Sadowsky (Co-Presenter/Co-Author), BioTechnology Institute, University of Minnesota, sadowsky@umn.edu;

5/18/2015  |   11:30 - 11:45   |  102C

COMPARISON OF DIEL NITROGEN FIXATION FLUX MEASUREMENTS In streams with low nitrate concentrations, nitrogen fixation is a dominant process to form biologically available nitrogen for biofilm growth. Diel patterns in nitrogen fixation will control the net nitrogen flux. Acetylene reduction assays are an indirect method of measuring nitrogen fixation by assessing nitrogenase activity while membrane-inlet mass spectrometers (MIMS) directly measure nitrogen gas concentration and net nitrogen fixation. To compare diel nitrogen fixation methods, we incubated chamber assays to measure acetylene reduction and the change in nitrogen, oxygen, and argon gases to calculate net nitrogen fixation using MIMS in oligotrophic Wyoming streams. Nitrogen fixation estimated via acetylene reduction ranged from 0.043 mg N₂ m^-2 hr^-1 at night to 0.24 mg N₂ m^-2 hr^-1 fixed during the day. Net nitrogen fixation using the MIMS technique was much higher than the acetylene reduction method and ranged from 0.39 mg N₂ m^-2 hr^-1 to -3.59 mg N₂ m^-2 hr^-1 and was related to increased solar radiation and net ecosystem productivity which ranged from -18.59 mg O₂ m^-2 hr^-1 to 101.77 mg O₂ m^-2 hr^-1.

Hilary Madinger (Primary Presenter/Author), University of Wyoming, hilary.madinger@gmail.com;


Lisa Kunza (Co-Presenter/Co-Author), South Dakota School of Mines and Technology, lisa.kunza@sdsmt.edu;


Robert O. Hall (Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;


Jaime Haueter (Co-Presenter/Co-Author), South Dakota School of Mines and Technology, jaime.haueter@mines.sdsmt.edu;

5/18/2015  |   11:45 - 12:00   |  102C

SALINITY EFFECTS ON NITROGEN CYCLING IN TIDAL WETLANDS OF THE HUDSON RIVER Salinity intrusion affecting tidal freshwater marshes is expected to have several effects on nitrogen cycling primarily mediated by toxic effects of sulfide (derived from sulfate reduction) on enzymes responsible for steps in the nitrogen cycle. Dissolved nitrogen in tidal exchange water was measured at five marshes spanning the fresh-brackish region of the lower Hudson River estuary. Denitrification potential was measured in sediments from these sites and an experimental manipulation of salinity was used to assess effects on nitrogen processing. The five marshes showed similar patterns in nitrate across tidal exchanges with all sites showing ebb-tide concentrations roughly half flood-tide concentrations. These patterns suggest minimal differences among sites in net nitrate removal. Experimental manipulation of salinity spanned a greater range in salt content than experienced by the field sites at times of sampling. These experiments did reveal inhibition of both nitrification and denitrification at highest levels of salinity. While high salinity clearly can affect N-cycling in these marshes the present exposure levels are apparently not causing large changes in how these marshes process nitrogen.

Stuart Findlay (Primary Presenter/Author), cARY iNSTITUTE OF eCOSYSTEM sTUDIES, findlays@caryinstitute.org;


Melody Bernot (Co-Presenter/Co-Author), Ball State University, mjbernot@bsu.edu;