Tuesday, June 6, 2017
11:00 - 12:30

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11:00 - 11:15: / 306A MEASURING UPTAKE OF ORGANIC AND INORGANIC PHOSPHORUS USING EXPERIMENTAL STREAMS

6/06/2017  |   11:00 - 11:15   |  306A

Measuring uptake of organic and inorganic phosphorus using experimental streams Excess phosphorus (P) from surrounding agricultural land use degrades the quality of adjacent and downstream waterways. Most researchers measure P as soluble reactive phosphate (SRP) or total phosphorus (TP), but bioavailable P exists along the continuum between these, and in various forms (e.g., organic vs. inorganic P). Therefore, the relative importance of microorganisms for removing P from overlying water may be underestimated with current methods, especially in agricultural systems where P can be loosely sorbed to organic matter. To understand the relationship between form and function, we measured P uptake using short-term additions of inorganic potassium phosphate and organic reconstituted manure pellets in experimental low-P streams where we expect high biological demand. Uptake lengths (Sw) for the inorganic release were similar when calculated with SRP and TP (15m and 19m, respectively). Using the manure solution, Sw-SRP was an order of magnitude shorter than Sw-TP (59m and 1000m, respectively). We will explore these P uptake patterns further using a new yeast-based P measurement being developed to estimate bioavailable P in both the experimental streams at ND-LEEF and in the field in agricultural streams.

Matt T. Trentman (Primary Presenter/Author), University of Notre Dame, mtrentma@nd.edu;


Jennifer L. Tank ( Co-Presenter/Co-Author), University of Notre Dame, tank.1@nd.edu;


Holly Goodson ( Co-Presenter/Co-Author), University of Notre Dame, holly.v.goodson.1@nd.edu ;


Brett Peters ( Co-Presenter/Co-Author), University of Notre Dame, Brett.W.Peters.48@nd.edu;


Yueh-Fu Wu ( Co-Presenter/Co-Author), University of Notre Dame, Yueh-Fu.Wu.94@nd.edu;


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11:15 - 11:30: / 306A DO NITROGEN FIXATION AND DENITRIFICATION CO-OCCUR ACROSS A GRADIENT OF STREAM N CONCENTRATIONS IN A WESTERN WATERSHED?

6/06/2017  |   11:15 - 11:30   |  306A

DO NITROGEN FIXATION AND DENITRIFICATION CO-OCCUR ACROSS A GRADIENT OF STREAM N CONCENTRATIONS IN A WESTERN WATERSHED? It is frequently assumed that N2 fixation and denitrification do not co-occur in streams because they are favored under different concentrations of reactive nitrogen. Yet, this assumption has not been evaluated because both processes are rarely quantified in the same stream. We asked if these processes could co-exist by measuring rates of N2 fixation using acetylene reduction, denitrification using acetylene block, and net N2 flux using membrane inlet mass spectrometry on rocks and sediment in 8 southeastern Idaho streams encompassing a dissolved inorganic nitrogen (DIN) gradient of 6-615 µg/L. N2 fixation and denitrification rates were 0-218 and 0.41-5.66 µg N/m2/hr, respectively. The highest N2 fixation rates occurred in streams with the lowest DIN concentrations, and denitrification rates generally increased with increasing DIN. However, low rates of both processes occurred across the full gradient, suggesting DIN concentration alone cannot predict their occurrence. In two streams we made measurements of high spatial resolution and found high rates of both processes occurred in close proximity to one another, suggesting that small-scale variation in substrate and environmental conditions facilitates the co-occurrence of these processes.

Erin Eberhard (Primary Presenter/Author), Michigan Technological University , ekeberha@mtu.edu;


Amy Marcarelli ( Co-Presenter/Co-Author), Michigan Technological University, ammarcar@mtu.edu;


Colden Baxter ( Co-Presenter/Co-Author), Idaho State University, baxtcold@isu.edu;


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11:30 - 11:45: / 306A FACTORS INFLUENCING THE RELATIIVE CONTRIBUTION OF LARGE AND SMALL STREAMS TO WHOLE-NETWORK DENITRIRIFCAITON

6/06/2017  |   11:30 - 11:45   |  306A

FACTORS INFLUENCING THE RELATIIVE CONTRIBUTION OF LARGE AND SMALL STREAMS TO WHOLE-NETWORK DENITRIRIFCAITON Variation in denitrification rates across stream networks is influenced by multiple factors including stream network chemistry, biology and hydrology. We use a stream network simulation model to isolate the effects of nitrate concentration and whole-stream respiration rate on denitrification from all other effects by varying hillslope concentration and stream respiration rates while holding all other variables constant. Our model estimates denitrification based on empirical relationships among denitrification uptake velocity, stream nitrate concentration, and stream respiration rate, with respiration rates related to stream temperature via an Arrhenius-type relationship. Simulation results reveal the effects of hillslope nitrate concentration and stream respiration rate on geospatial patterns of total and fractional denitrification uptake. In stream networks which remove a large portion of incoming nitrate, we demonstrate that the depletion of nitrate concentration across the network results in higher denitrification rates in small streams than in large streams. Alternatively, in stream networks with proportionally small nitrate removal, we demonstrate that elevated respiration rates in larger, warmer streams lead to higher denitrification rates.

Sam Carlson (Primary Presenter/Author), Montana State University, sam.p.carlson@gmail.com;


Geoffrey Poole ( Co-Presenter/Co-Author), Montana State University, Montana Institute on Ecosystems, gpoole@montana.edu ;


Robert Hall ( Co-Presenter/Co-Author), University of Wyoming, BHall@uwyo.edu;


Ellen Wohl ( Co-Presenter/Co-Author), Colorado State University, ellenw@warnercnr.colostate.edu ;


David Walters ( Co-Presenter/Co-Author), US Geological Survey, waltersd@usgs.gov;


Michael Venarsky ( Co-Presenter/Co-Author), Colorado State University, mvenarsky@gmail.com;


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11:45 - 12:00: / 306A BETTER ESTIMATES OF STREAM GAS EXCHANGE USING ARGON RATHER THAN SULFUR HEXAFLUORIDE

6/06/2017  |   11:45 - 12:00   |  306A

BETTER ESTIMATES OF STREAM GAS EXCHANGE USING ARGON RATHER THAN SULFUR HEXAFLUORIDE Gas exchange is a parameter needed in stream metabolism and trace gas emissions models. Estimates of oxygen (O2) gas exchange using sulfur hexafluoride (SF6) need to be scaled by their Schmidt number ratio, but this scaling is uncertain under conditions of high gas exchange via bubbles. Because argon (Ar) and O2 have nearly identical Schmidt numbers and we can easily measure Ar using membrane inlet mass spectrometry, using Ar additions to measure gas exchange provides a better estimate of stream gas exchange to inform metabolism models. The mean ratio of gas exchange from Ar and SF6 methods in a hierarchical exponential decay model was 1.84 (credible interval 1.00-2.64) compared to the expected 1.35. We found that SF6 underestimated gas exchange in steep streams with high bubble mediated gas transfer. Additionally, estimates of gas exchange using metabolism estimates from diel O2 concentrations in a hierarchical Bayesian oxygen model produced similar results to the estimates from Ar additions. Because Ar is a better proxy for O2 and is easily measured, we suggest using Ar additions to measure stream gas exchange.

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


Robert Hall ( Co-Presenter/Co-Author), University of Wyoming, BHall@uwyo.edu;


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12:00 - 12:15: / 306A TOWARDS PREDICTING SPATIAL VARIATION IN NITRATE RETENTION AND DENITRIFICATION AT THE GROUNDWATER-SURFACE WATER INTERFACE IN SANDY STREAMS

6/06/2017  |   12:00 - 12:15   |  306A

TOWARDS PREDICTING SPATIAL VARIATION IN NITRATE RETENTION AND DENITRIFICATION AT THE GROUNDWATER-SURFACE WATER INTERFACE IN SANDY STREAMS Groundwater-surface water ecotones present opportunities for nitrate retention because changes in organic carbon availability, redox potential and nitrate demand often occur at these locations. We identified spatial variation in nitrate retention and denitrification in shallow groundwater associated with sandy streams in Wisconsin, towards the ultimate goal of predicting the locations of nitrate removal. We hypothesized that groundwater nitrate removal would be optimized at intermediate rates of groundwater discharge, where microbes are exposed to suitable redox conditions for nitrate reduction and where groundwater delivers a moderate supply of nitrate to reaction sites. Three study streams were chosen that spanned an order of magnitude in groundwater nitrate concentration (2 to 20 mg NO3-N/L). Groundwater discharge was estimated by applying Darcy’s Law to standard measurements at piezometer locations. Nitrate and N2 concentrations were measured at discrete points along 60 cm groundwater flow paths using MINIPOINT samplers. Nitrate retention and denitrification (MIMS) were quantified by determining how nitrate and N2 fluxes changed along the flow paths. Nitrate retention and denitrification rates were nonlinearly related to DO concentration and groundwater discharge rate but patterns were site-specific.

Robert Stelzer (Primary Presenter/Author), Department of Biology, University of Wisconsin Oshkosh, stelzer@uwosh.edu;


Thad Scott ( Co-Presenter/Co-Author), Baylor University, Thad_Scott@baylor.edu ;


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12:15 - 12:30: / 306A THE STREAM FEASTS WHILE THE FOREST LEAKS: IN-STREAM AND WATERSHED RESPONSES TO A WHOLE WATERSHED ACID MITIGATION EXPERIMENT

6/06/2017  |   12:15 - 12:30   |  306A

THE STREAM FEASTS WHILE THE FOREST LEAKS: IN-STREAM AND WATERSHED RESPONSES TO A WHOLE WATERSHED ACID MITIGATION EXPERIMENT Many headwater streams across the Northeast U.S. bear strong legacies of acid precipitation, despite long term declines in deposition. At Hubbard Brook, an experimental attempt to remediate decades of soil acidification successfully promoted forest growth and increased soil pH, but also generated dramatic increases in watershed nitrogen export. This experiment may provide an accelerated view into possible long-term trajectories of ecosystem recovery from acid precipitation. Here, we examine how the watershed acid remediation treatment has altered in-stream processing of nitrogen. We found that the treatment stream acted as a substantial net sink of nitrate during the growing season. During baseflow periods, nitrate flux declined by 15-55% along a 500m reach, despite a 2.4-fold increase in discharge over the same reach. By contrast, nitrate flux in the reference watershed increased monotonically with discharge. High nitrate export from the treatment watershed became more coupled to storm events, and denitrification potential increased threefold in treatment sediments. These results suggest that under ecosystem recovery from acid precipitation, aquatic ecosystems may act as substantial sinks of N, even as terrestrial ecosystems may become greater sources.

Richard Marinos (Primary Presenter/Author), Duke University, rem31@duke.edu;


Emily Bernhardt ( Co-Presenter/Co-Author), Duke University, ebernhar@duke.edu;


Emma Rosi ( Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, rosie@caryinstitute.org;


Lindsey Rustad ( Co-Presenter/Co-Author), USFS Northern Research Station, lrustad@usfs.gov;


John Campbell ( Co-Presenter/Co-Author), US Forest Service, Northern Research Station, jcampbell@fs.fed.us;


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


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