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SFS Annual Meeting

Tuesday, May 22, 2018
09:00 - 10:30

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09:00 - 09:15: / 330 B USING EXPERIMENTAL STREAMS TO UNDERSTAND THE ROLE OF BIOFILM COLONIZATION AND DISTURBANCE IN ESTIMATING REAERATION USING ARGON GAS AS A DIRECT TRACER AT ND-LEEF

5/22/2018  |   09:00 - 09:15   |  330 B

USING EXPERIMENTAL STREAMS TO UNDERSTAND THE ROLE OF BIOFILM COLONIZATION AND DISTURBANCE IN ESTIMATING REAERATION USING ARGON GAS AS A DIRECT TRACER AT ND-LEEF Estimating the exchange of gasses between the stream water and the atmosphere poses a methodological challenge for researchers, given the difficulties of making accurate gas measurements in flowing waters. Reaeration is an important driver influencing the estimation of biogeochemical budgets such as whole-stream metabolism. Common tracers have proven problematic either because they are non-conservative (e.g., propane may be consumed via microbial activity) or methodologically problematic (e.g., SF6 is a potent greenhouse gas). The use of argon gas as a conservative tracer has recently been suggested as an alternative, and has been used successfully in the field. We tested the role of potential reaeration drivers (e.g., flow variation, substrate) using short-term direct injections of argon gas in four experimental streams at the ND-LEEF. We repeated additions over a five-month biofilm colonization sequence and under experimental disturbance scenarios to determine the role of abiotic and biotic factors on reaeration in small streams. Preliminary results suggest that substrate type can influence reaeration, with highest rates occurring on sand, while high biofilm coverage homogenizes estimates. Flooding conditions did not impact gas transfer in larger substrate streams, while significantly increasing reaeration in sandy streams.

Martha M. Dee (Primary Presenter/Author), University of Notre Dame, mdee@nd.edu;


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


Arial Shogren (Co-Presenter/Co-Author), University of Notre Dame, ashogren@nd.edu;


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


Shannon Speir (Co-Presenter/Co-Author), University of Notre Dame, sspeir@nd.edu;


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09:15 - 09:30: / 330 B GREENHOUSE GAS FLUXES FROM AQUATIC ECOSYSTEMS ALONG A RURAL TO URBAN GRADIENT ARE DRIVEN BY N LOADING

5/22/2018  |   09:15 - 09:30   |  330 B

GREENHOUSE GAS FLUXES FROM AQUATIC ECOSYSTEMS ALONG A RURAL TO URBAN GRADIENT ARE DRIVEN BY N LOADING The effects of urbanization on net greenhouse gas (GHG) exchange from streams and rivers to the atmosphere is poorly understood. Here we examine 4 years of weekly samples in multiple headwater streams and a downstream main stem site in New Hampshire. Our results show that within a single drainage network, CH4 concentrations are higher downstream than the headwaters, which span a range of land use and wetland coverage. Methane is also very strongly seasonal in concentration in the tributaries (peaking in late summer), but is aseasonal in the main stem. In contrast, N2O concentrations are strongly seasonal at all sites, but peak in early winter and are much higher in more urban tributaries than the main stem. Urbanization results in a flipping of GHG concentrations, with highest N2O and lowest CH4 in the most urban watershed. CO2 shows no strong patterns with respect to landscape position, urbanization, or season. We examined multiple biogeochemical drivers of net CH4 and N2O production, and found that the increased NO3 concentration associated with urbanization is a good predictor of N2O concentrations and NH4:NO3 is a good predictor of CH4 concentrations.

Jody Potter (Primary Presenter/Author), University of New Hampshire, jody.potter@unh.edu;


Adam Wymore (Co-Presenter/Co-Author), University of New Hampshire, adam.wymore@unh.edu;


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


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09:30 - 09:45: / 330 B SALINITY EFFECTS ON GREENHOUSE GAS EMISSIONS FROM WETLAND SOILS ARE CONTINGENT UPON HYDROLOGIC SETTING: A MICROCOSM EXPERIMENT

5/22/2018  |   09:30 - 09:45   |  330 B

SALINITY EFFECTS ON GREENHOUSE GAS EMISSIONS FROM WETLAND SOILS ARE CONTINGENT UPON HYDROLOGIC SETTING: A MICROCOSM EXPERIMENT Human appropriation of surface water and extensive ditching and draining of coastal plain landscapes are interacting with rising sea levels to increase the frequency of saltwater intrusion into freshwater coastal wetlands. We performed a full factorial experiment in which we exposed intact soil cores from a freshwater wetland to four experimental marine salt treatments and two hydrologic treatments. We measured the resulting treatment effects on the emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) over 90 days. We compared control treatments to artificial saltwater (target salinity of 5 ppt) and to two treatments that added sulfate alone and saltwater with the sulfate removed. We found that all marine salt treatments suppressed CO2 production, with these effects more pronounced in the flooded treatments. Surprisingly, CH4 fluxes from our flooded cores increased between 300 to 1200% relative to controls in both saltwater treatments, with the sulfate free saltwater treatment stimulating greater CH4 emissions. N2O emissions increased under drought and increased salinity. Our results demonstrate that saltwater enrichment of forested wetlands may enhance greenhouse gas emissions and that the magnitude and form of these emissions are contingent upon wetland hydrology.

Marcelo Ardon (Primary Presenter/Author), North Carolina State University, mlardons@ncsu.edu;


Ashley Helton (Co-Presenter/Co-Author), University of Connecticut, ashley.helton@uconn.edu;


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


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09:45 - 10:00: / 330 B PATCH DYNAMICS OF NITROGEN FIXATION AND DENITRIFICATION IN STREAMS

5/22/2018  |   09:45 - 10:00   |  330 B

PATCH DYNAMICS OF NITROGEN FIXATION AND DENITRIFICATION IN STREAMS Streams are characterized by a high degree of spatial heterogeneity at multiple, nested scales that, in turn, influences rates and variability in ecosystem processes. Patches are a feature of this heterogeneity that may facilitate the co-occurrence of biogeochemical processes thought to be incompatible, like N2 fixation and denitrification. To test this hypothesis we measured rates of N2 fixation and denitrification in patches of six Idaho and Michigan streams. The coefficient of variation (CV) among all streams (CV = 5.9) for N2 fixation rates was greater than the CV in each individual stream. For denitrification rates, two streams displayed the highest variability in denitrification (CV = 3.4 and 3.7, respectively), because these streams had lower frequency of organic matter patches with high denitrification rates, relative to other substrate with low or zero rates. To further analyze the variation of instream processes and the mechanisms that create these patches, we are assessing microbial gene abundance and a suite of surface and hyporheic characteristics. Understanding the mechanisms behind patches in stream ecosystems will lead to a better understanding of how the spatial structure of stream ecosystems can affect complex biogeochemical cycling.

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;


Stephen Techtmann (Co-Presenter/Co-Author), Michigan Technological University, smtechtm@mtu.edu;


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10:00 - 10:15: / 330 B INFLUENCE OF LOGJAMS ON DENITRIFICATION IN A MONTANE STREAM NETWORK

5/22/2018  |   10:00 - 10:15   |  330 B

INFLUENCE OF LOGJAMS ON DENITRIFICATION IN A MONTANE STREAM NETWORK In the North St. Vrain stream network, located in Rocky Mountain National Park, Colorado, valley morphology and land use determine logjam density, creating spatial heterogeneity in channel form and carbon storage. Such patterns influence stream respiration rates, thereby altering rates of denitrification and spatial patterns of nitrate removal from streams. We use a stream network simulation model that incorporates the effects of whole-stream respiration on denitrification to contextualize the potential impact of logjam-driven hotspots on whole-network denitrification. Our results suggest that carbon storage and changes to channel morphology associated with logjams create hotspots of denitrification that influence patterns of whole network nitrate removal. Further, our model suggests that land management actions which influence stream morphology may also alter stream 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 ;


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


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


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10:15 - 10:30: / 330 B EFFECT OF DAM REMOVALS ON BIOGEOCHEMICAL AND PHYSICAL PROCESSES

5/22/2018  |   10:15 - 10:30   |  330 B

EFFECT OF DAM REMOVALS ON BIOGEOCHEMICAL AND PHYSICAL PROCESSES Across the United States, advocacy of dam removals is increasing for reasons including restoring migratory fish passage, reestablishing more natural flow and sediment regimes, and decreasing threats to human safety from aging infrastructure. While these are justifiable concerns, the effect of dam-related impoundments on physical and biogeochemical processes and river network-scale water quality, and how these processes change when a dam is removed, are not entirely clear. Here, we take advantage of a planned dam removal on the Ipswich River in northeastern Massachusetts to investigate processes controlling nutrient transformations and removal, sediment retention, and greenhouse gas (GHG) production within impoundments. Preliminary results using high frequency in situ sensors reveal substantial nitrate (NO3) removal during the summer low flow period, and little to no impact during higher flows. Dissolved methane (CH4) was similar at the inflow and outflow across 2016 and 2017. However, CH4 concentrations were significantly greater in an off-channel area, suggesting lentic zones within impoundments may be sizable sources of GHGs to the atmosphere. This project will aid in understanding how dam removals affect nutrient and sediment fluxes and GHG production and will help inform future dam removal projects.

Christopher Whitney (Primary Presenter/Author), University of New Hampshire, chris.whitney@unh.edu;


Wilfred Wollheim (Co-Presenter/Co-Author), University of New Hampshire, wil.wollheim@unh.edu;


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