Monday, June 5, 2017
14:00 - 15:45

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14:00 - 14:15: / 306A THE INFLUENCE OF CLADOPHORA ALGAE ON PHYSICOCHEMICAL AND BIOGEOCHEMICAL CONDITIONS OF THE UPPER CLARK FORK RIVER, MONTANA

6/05/2017  |   14:00 - 14:15   |  306A

THE INFLUENCE OF CLADOPHORA ALGAE ON PHYSICOCHEMICAL AND BIOGEOCHEMICAL CONDITIONS OF THE UPPER CLARK FORK RIVER, MONTANA Cladophora glomerata routinely generates nuisance blooms in the Upper Clark Fork River, MT. This study characterized the influence of biomass on how conditions of the benthic environment may differ from the overlying water column throughout the growing season. Biomass and biogeochemical conditions were monitored at three sites over roughly 150 river km. Abundance of benthic organic matter (BOM) was tracked along with stream physical and chemical features. Localized sampling of near-bottom and water-column physicochemical (DO, % saturation, temperature, ORP, pH) and biogeochemical (NH??, NO??, SRP, DOC) character provided measures of conditions in these two zones of the river. River-average biomass (as AFDM, g/m²) peaked at 168.8 (± 32.2 SE) during June and then declined to 10.5 (± 3.4 SE) by September. DO concentrations in the benthic zone were consistently lower than in the water column (paired t-test, P < 0.001). Benthic isolation indices were calculated to compare conditions between zones as an arithmetic ratio, absolute difference, and a normalized difference. Preliminary data suggest differences in habitat conditions between the two zones may be related to BOM abundance and physicochemical conditions.

Nicholas Banish (Primary Presenter/Author), University of Montana, nicholas.banish@umontana.edu;


Marc Peipoch ( Co-Presenter/Co-Author), University of Montana, Division Biological Sciences, marc.peipoch@mso.umt.edu;


H. Maurice Valett ( Co-Presenter/Co-Author), University of Montana, maury.valett@umontana.edu;


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14:15 - 14:30: / 306A GLOBAL BOUNDS ON GASEOUS NITROGEN LOSS FROM TROPICAL FOREST WATERSHEDS

6/05/2017  |   14:15 - 14:30   |  306A

GLOBAL BOUNDS ON GASEOUS NITROGEN LOSS FROM TROPICAL FOREST WATERSHEDS Humid tropical forests dominate denitrification from unmanaged lands, but there is large uncertainty about the range and drivers of N gas emissions across the biome. We combined pantropical measures of stream chemistry with ecosystem modeling to determine total N gas losses and associated uncertainty across tropical forest watersheds. We document a negative relationship between nitrate and dissolved organic carbon (DOC) across watersheds and find that the probability of a missing N sink was highest in watersheds with high DOC, consistent with the imprint of dissimilatory nitrate reduction. We find a large range in gaseous fluxes depending on whether denitrification is modeled occurring downstream of terrestrial plant uptake or competing with plant uptake. Combined, denitrification in soils and along soil-to-stream hydrologic flowpaths constitute >45% of total N losses. We place an upper bound on soil denitrification of ~80% of total N losses beyond which tropical plant growth would be compromised. Our simulations indicate that terrestrial soils dominate denitrification but also reveal globally significant levels of gaseous N loss from aquatic environments that are roughly equivalent to inputs via atmospheric deposition.

Jack Brookshire (Primary Presenter/Author), Montana State University, jbrookshire@montana.edu;


Stefan Gerber ( Co-Presenter/Co-Author), University of Florida, sgerber@ufl.edu;


Steven Thomas ( Co-Presenter/Co-Author), School of Natural Resources, University of Nebraska-Lincoln, Lincoln, sthomas5@unl.edu;


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14:30 - 14:45: / 306A REAL-TIME NITRATE DATA PROVIDE INSIGHTS INTO NITRATE-N EXPORT DURING STORMS IN TWO CONTRASTING AGRICULTURAL WATERSHEDS

6/05/2017  |   14:30 - 14:45   |  306A

REAL-TIME NITRATE DATA PROVIDE INSIGHTS INTO NITRATE-N EXPORT DURING STORMS IN TWO CONTRASTING AGRICULTURAL WATERSHEDS Accurately estimating watershed nutrient export can be challenging as traditional monitoring approaches using grab samples often underestimate nutrient loads during storms. Continuous nitrate-N sensors offer an opportunity to examine nutrient dynamics on a more resolved temporal scale that could help document benefits of conservation and restoration. We deployed continuous nitrate-N sensors in two agricultural watersheds in northern Indiana where agricultural conservation practices are being adopted at the watershed scale. We used the high-resolution data to evaluate nitrate-N export during storms in the Shatto Ditch (SDW) and Kirkpatrick Ditch Watersheds (KDW). Nitrate-N loads varied with storm size in SDW and increased linearly with storm size until direct runoff was >80% of total flow, yet there was no dilution effect in SDW. In contrast, in KDW, nitrate-N concentrations decreased during large storms suggesting dilution. Despite minimal increase in nitrate-N concentrations with the largest storms in both watersheds, we observed significant increases in nitrate-N loads leaving both watersheds. High-resolution nutrient data will be critical in quantifying the impacts of conservation by improving estimates of nutrient export during critical periods such as storms.

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


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


Todd V. Royer ( Co-Presenter/Co-Author), Indiana University Bloomington, troyer@indiana.edu;


Ursula H. Mahl ( Co-Presenter/Co-Author), University of Notre Dame, umahl@nd.edu;


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


Brittany Hanrahan ( Co-Presenter/Co-Author), University of Notre Dame, bhanrah3@nd.edu;


Kara Prior ( Co-Presenter/Co-Author), Indiana University, kprior@indiana.edu;


Sheila Christopher ( Co-Presenter/Co-Author), University of Notre Dame, sheila.christopher@nd.edu;


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14:45 - 15:00: / 306A SEASONAL DYNAMICS OF EXTRACELLULAR ENZYME ACTIVITY AND NUTRIENT AVAILABILITY WITHIN AN AGRICULTURALLY INFLUENCED OXBOW LAKE

6/05/2017  |   14:45 - 15:00   |  306A

SEASONAL DYNAMICS OF EXTRACELLULAR ENZYME ACTIVITY AND NUTRIENT AVAILABILITY WITHIN AN AGRICULTURALLY INFLUENCED OXBOW LAKE We examined seasonal patterns in water column nutrients, sediments, chlorophyll a (chl. a) and extracellular enzyme activity (EEA) within a remnant oxbow lake to assess relationships between nutrient availability and EEA. Chl. a was limited by total solids (TS) concentrations > 123 mg/L which occurred throughout winter and early spring. Rising chl. a concentrations from May thru September corresponded with sharp declines in dissolved inorganic nitrogen (DIN) in early summer coupled with more gradual declines in dissolved inorganic phosphorus (DIP). Patterns in Beta-N-acetylglucosaminindase (NAG) + l-leucine aminopeptidase (LAP) activity peaked in late august during a period of near maximum chl. a concentrations and consistently low DIN, whereas acid phosphatase (AP) activity peaked in late September when chl. a was still high and DIP reached its annual minimum. Michaelis-Menten dynamics explained the response of algal growth to experimental N and P gradients in bioassays using summer plankton communities. Algal bioassays also confirmed that increasing DIP availability suppressed AP activity whereas increasing NAG + LAP activity appeared to be more related to increasing algal biomass than decreasing DIN.

Jason M. Taylor (Primary Presenter/Author), USDA, Agricultural Research Service, National Sedimentation Lab, jason.taylor@ars.usda.gov;


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15:00 - 15:15: / 306A EVIDENCE FOR PRIMING: LIGHT DEGRADED DISSOLVED ORGANIC MATTER INCREASED THE DECAY RATE OF TERRESTRIAL ORGANIC MATTER IN EXPERIMENTAL STREAMS

6/05/2017  |   15:00 - 15:15   |  306A

EVIDENCE FOR PRIMING: LIGHT DEGRADED DISSOLVED ORGANIC MATTER INCREASED THE DECAY RATE OF TERRESTRIAL ORGANIC MATTER IN EXPERIMENTAL STREAMS Dissolved organic matter (DOM) is the largest pool of organic matter (OM) in aquatic systems and mediates all microbial processes. Biogeochemists have described priming, the process when additions of labile OM accelerate decomposition of semi-labile OM. We tested for priming of terrestrial, semi-labile DOM in 8 experimental streams and dark bottles. Decay of 2 forms of semi-labile DOM, soil leachate and plant leachate, 2 forms of labile DOM, algal leachate and light degraded semi-labile DOM, and a mixture of labile and semi-labile DOM were measured. Decay rates of soil leachate were too low to measure and plant leachate decay averaged 0.011/hr in streams and 0.001/hr in bottles (S.D. 0.002/hr ; 0.001/hr). Algal leachate decay averaged 0.025/hr in streams and 0.005/hr in bottles (S.D. 0.021/hr ; 0.002/hr). When algal leachate was mixed with semi-labile plant leachate decay rates were similar to plant leachate alone. However, when light-degraded plant leachate was added to semi-lable leachate, decay rates were greater than plant leachate alone. We concluded exposure to light increased lability of terrestrially derived DOM, and could increase consumption rates of non-labile DOM.

Julie Kelso (Primary Presenter/Author), Utah State University, julia.kelso@gmail.com;


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


Michelle Baker ( Co-Presenter/Co-Author), Utah State University, michelle.baker@usu.edu;


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15:15 - 15:30: / 306A THE IMPORTANCE OF DENITRIFICATION ASSOCIATED WITH MACROPHYTE BEDS IN REDUCING NITRATE EXPORT FROM A SUBTROPICAL RIVER

6/05/2017  |   15:15 - 15:30   |  306A

The importance of denitrification associated with macrophyte beds in reducing nitrate export from a subtropical river Denitrification in rivers can play a key role in reducing excessive nitrogen loading from catchments, removing up to 50%. This reduces coastal eutrophication and the likelihood of algal blooms. The presence of macrophyte beds enriches sediments with organic carbon thus promoting denitrification. However, there is limited knowledge of denitrification associated with macrophytes in subtropical rivers. To tackle this question we measured denitrification rates in sediment with and without macrophytes at six sites in the upper Brisbane River, Queensland, Australia. Using the isotope pairing technique we quantified the denitrification of water column nitrate diffusing into sediments and the rate of coupled nitrification-denitrification within sediments. Denitrification rates were 2-50 fold higher in macrophyte sediments compared to bare sediments at five of the sites. Sediments in macrophyte beds had a higher organic carbon content and lower porosity than bare sediments. Using this data we estimated the potential reduction in downstream nitrate transport possible under different macrophyte coverage scenarios. This work highlights the need to consider macrophyte cover when modelling nitrogen losses from catchments with implications worldwide. Additionally, understanding the environmental conditions controlling denitrification is important to guide river restoration to enhance nitrogen removal.

Hannah Franklin (Primary Presenter/Author), Australian Rivers Institute, Griffith University, Queensland, Australia, h.franklin@griffith.edu.au;


Kate Smolders ( Co-Presenter/Co-Author), Seqwater, Queensland, Australia, k.smolders@seqwater.com.au;


Michele Burford ( Co-Presenter/Co-Author), Australian Rivers Institute, Griffith University, Queensland, Australi, m.burford@griffith.edu.au;


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15:30 - 15:45: / 306A PARTITIONING THE ROLE OF BIOLOGY AND SEASONALITY IN DIEL SOLUTE SIGNALS FROM TWO RIVER NETWORKS OF CONTRASTING LAND USE

6/05/2017  |   15:30 - 15:45   |  306A

PARTITIONING THE ROLE OF BIOLOGY AND SEASONALITY IN DIEL SOLUTE SIGNALS FROM TWO RIVER NETWORKS OF CONTRASTING LAND USE Quantifying the relative role of nitrogen (N) uptake processes at the stream network scale is challenging, but empirical data are needed to refine models of N transport and retention in lotic ecosystems. Recently, open-channel methods have facilitated measurements of reach-scale metabolism and denitrification, allowing for partitioning of biological N removal into assimilatory vs. dissimilatory processes. We compared diel signals of dissolved solutes and gasses across seasons in a tributary and mainstem reach in two watersheds of contrasting land use: the Manistee (MI; 83% forested) and Tippecanoe (IN; 82% agricultural). We estimated metabolism and assimilatory N uptake using continuous measurements of dissolved oxygen and NO3-N. During these 36-hour sampling campaigns, we collected dissolved N2 samples to estimate reach-scale denitrification using membrane-inlet mass spectrometry. In summer, assimilatory uptake dominated NO3-N removal in the agricultural Tippecanoe during peak macrophyte growth, while denitrification drove NO3-N removal in the forested Manistee. After macrophyte senescence, denitrification controlled NO3-N removal in the Tippecanoe. Diel measurements of dissolved gasses and solutes in these two contrasting systems strengthen the temporal, spatial, and seasonal context of N dynamics in stream networks.

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;


Timothy Hoellein ( Co-Presenter/Co-Author), Loyola University Chicago, thoellein@luc.edu;


Alexander Reisinger ( Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, reisingera@caryinstitute.org;


Alessandra Marzadri ( Co-Presenter/Co-Author), Center for Ecohydraulics Research, University of Idaho , marzadri@ing.unitn.it;


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