Wednesday, June 7, 2017
09:00 - 10:30

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09:00 - 09:15: / 306A METABOLISM IN AN AGRICULTURAL STREAM: EVEN IMPACTED RIVERSCAPES RETAIN LONGITUDINAL COMPLEXITY

6/07/2017  |   09:00 - 09:15   |  306A

METABOLISM IN AN AGRICULTURAL STREAM: EVEN IMPACTED RIVERSCAPES RETAIN LONGITUDINAL COMPLEXITY Stream metabolism is an integrative measure of ecosystem function which responds to shifts in biomass, flow, temperature, and light. While metabolism is well understood in temperate systems, we know less about the spatial and temporal variability of metabolism in semi-arid regions. Marsh Creek, an agriculturally impacted stream in southeastern Idaho, is characterized by high turbidity, yet is also subject to large floating macroalgal blooms (<12% of stream surface area during peak growing season). We measured daily ecosystem metabolism at 6 locations along ~75 km of Marsh Creek to understand within-stream controls on metabolism over one year. Our initial results suggest different spatial and temporal drivers of metabolism. Despite our expectation that turbidity would dampen gross primary production, we found the highest rates of gross primary production in the most turbid site. However, within sites, GPP was negatively associated with turbidity. In spite of extensive stream modification and channelization, we find longitudinal heterogeneity in biomass production, sedimentation, and nutrient levels. Our results reveal that complex interactions drive stream metabolism, even in highly modified landscapes.

Sarah Stalder (Primary Presenter/Author), Idaho State University, stalsara@isu.edu;


Rebecca Hale ( Co-Presenter/Co-Author), Idaho State University, halereb3@isu.edu;


Benjamin Crosby ( Co-Presenter/Co-Author), Idaho State University, crosby@isu.edu;


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


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09:15 - 09:30: / 306A BIOAVAILABLE DISSOLVED ORGANIC CARBON IN MID-ORDER STREAMS VARIES ACROSS GRADIENTS OF ANTHROPOGENIC SOURCES

6/07/2017  |   09:15 - 09:30   |  306A

BIOAVAILABLE DISSOLVED ORGANIC CARBON IN MID-ORDER STREAMS VARIES ACROSS GRADIENTS OF ANTHROPOGENIC SOURCES Dissolved organic carbon (DOC) is a critical driver of heterotrophic stream processes, but not all DOC delivered to streams is of the same quality to microbes. Anthropogenic sources variably influence stream DOC quantity, but consistently increase the bioavailability of the DOC pool. We measured bioavailable DOC (BDOC) in mid-order streams in northeast Oklahoma and northwest Arkansas with 28 day incubation assays on water grab samples. Sites were chosen to span gradients of anthropogenic impacts to assess the influence of DOC source (e.g., pasture, forest, wastewater effluent) on DOC lability. DOC, and therefore BDOC, was below detection limits in forest-dominated streams. Streams with pasture-dominated catchments had variable but greater proportions of BDOC than forested catchments (0-20% of DOC removed during assays). Streams in urbanizing catchments with municipal wastewater discharges had consistently elevated BDOC (15-22%). These data were collected during a low flow event, and suggest that surface runoff may influence detection of land use patterns in stream DOC quality via export of low quantities of DOC. Sampling is occurring monthly to further investigate this relationship.

Caleb J. Robbins (Primary Presenter/Author), Baylor University, Caleb_Robbins@baylor.edu;


Jeffrey A. Back ( Co-Presenter/Co-Author), Baylor University, Jeff_Back@baylor.edu;


Ryan S. King ( Co-Presenter/Co-Author), Baylor University, Ryan_S_King@baylor.edu;


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09:30 - 09:45: / 306A HIGH FREQUENCY MEASURES OF NITRATE AND OXYGEN ALLOW PARSING OF STREAM CONTROL ON WATERSHED NITRATE EXPORT

6/07/2017  |   09:30 - 09:45   |  306A

HIGH FREQUENCY MEASURES OF NITRATE AND OXYGEN ALLOW PARSING OF STREAM CONTROL ON WATERSHED NITRATE EXPORT Elements leave watersheds in part via the streams that drain them, thus processing by streams has the final control over patterns of small watershed nutrient export. We used diel variation in nitrate concentration as a proxy for autotrophic nitrate uptake in a small Rocky Mountain stream. Prior to snowmelt, we installed nitrate and oxygen sensors to recorded at sub-hourly time intervals. Nitrate data peaked in concentration from snowpack flushing immediately after snowmelt followed by a steady dilution decline and then an increase in concentration at autumn baseflow. At the daily scale, nitrate concentrations declined 15% each day; this decline corresponded exactly with light suggesting control by stream autotrophs. Using oxygen data, we estimated reach-scale gross primary production and calculated the nitrogen demand from this carbon fixation at 1.4 mmol N m-2d-1. Calculated uptake from the diel nitrate decline was close at 0.5 to1.0 mmol N m-2d-1. Annual export was 800 mol nitrate-N/y, while biotic uptake was only 2%. High frequency N measures allow parsing biotic and hydrologic controls on watershed N export.

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


Elizabeth Traver ( Co-Presenter/Co-Author), University of Wyoming, TRAVER@uwyo.edu;


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09:45 - 10:00: / 306A SURFACE CARBON AND NITROGEN ACCRETION RATES IN THE MODERN SEDIMENT PROFILE OF WETLANDS THAT REPRESENT MULTIPLE STATES IN THE NORTH CAROLINA COAST

6/07/2017  |   09:45 - 10:00   |  306A

SURFACE CARBON AND NITROGEN ACCRETION RATES IN THE MODERN SEDIMENT PROFILE OF WETLANDS THAT REPRESENT MULTIPLE STATES IN THE NORTH CAROLINA COAST Coastal freshwater wetlands provide important ecosystem services but are vulnerable to saltwater incursion, drought, and inundation as our climate changes. Our study focuses on the causes and consequences of coastal freshwater forested wetlands transitioning to brackish and saltwater marshes along salinity gradients in the Albemarle-Pamlico peninsula of North Carolina. We are using a combination of approaches including biogeochemical analyses of soil cores to examine nitrogen and carbon cycles; geospatial analysis of spectral data to map wetland change; and citizen-science based mobile device applications for collecting pictures and locations of cypress trees. Our results to date indicate forested wetlands, transitional wetlands, marshes, and open water sites with saltwater stress average accretion rates of 0.21±0.04cm/yr, 0.17±0.04cm/yr, 0.12±0 cm/yr, and 0.23±0.05cm/yr respectively, which is lower than global average rate of sea level rise. There is no difference in percent carbon across wetlands types, but soil percent nitrogen is higher in marshes. Results to date suggest all wetlands in this region are vulnerable to sea level rise, and state transitions will alter the provision of ecosystem services.

Gillian Gundersen (Primary Presenter/Author), North Carolina State University, gcgunder@ncsu.edu;


Reide Corbett ( Co-Presenter/Co-Author), East Carolina University, CORBETTD@ecu.edu ;


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


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10:00 - 10:15: / 306A STREAM HABITAT CHARACTERISTICS INFLUENCING METHANE CONCENTRATION IN NORTH BUFFALO CREEK, GREENSBORO, NC

6/07/2017  |   10:00 - 10:15   |  306A

STREAM HABITAT CHARACTERISTICS INFLUENCING METHANE CONCENTRATION IN NORTH BUFFALO CREEK, GREENSBORO, NC Methanogens utilize reactants found naturally or as a result of the breakdown of organic matter to produce methane through a process called methanogenesis. This process requires anoxic conditions, and readily happens in the sediments of aquatic ecosystems. The amount of methane initially produced by methanogens in stream sediments is dependent on several factors. A survey of thirteen sites located along North Buffalo Creek (NBC), in Greensboro, NC was performed during the Winter of 2015. Data analysis suggests that stream sediment composition (sandy vs. coarser substrate) and the amount of undisturbed riparian zone influence methane concentrations in streamwater and porewater. Sandy sediments potentially provide more suitable anoxic microhabitats for methanogens. Increased organic inputs from undisturbed riparian zones could be providing reactants required for in-stream methanogenesis. Intact riparian zones could also influence methane concentrations in streams through subsurface inputs of methane. However more research is needed to determine how substrate composition and riparian vegetation influence stream methane cycle processes.

Joshua Brigham (Primary Presenter/Author), University of North Carolina Greensboro, jsbrigha@uncg.edu;


Anne Hershey ( Co-Presenter/Co-Author), The University of North Carolina at Greensboro, aehershe@uncg.edu;


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10:15 - 10:30: / 306A QUANTIFYING THE ROLE OF FLOW-CONNECTION IN STREAM NETWORK CARBON PATTERNS WITH SPATIAL STATISTICAL MODELS

6/07/2017  |   10:15 - 10:30   |  306A

QUANTIFYING THE ROLE OF FLOW-CONNECTION IN STREAM NETWORK CARBON PATTERNS WITH SPATIAL STATISTICAL MODELS Carbon quantity is variable across stream networks as a result of multi-scale processes occurring both in streams and in watersheds. The objectives of this study were to describe type (e.g., patch, gradient) and scale (e.g., patch size) of [DOC] patterns, evaluate which watershed (i.e., aspect, area, elevation, slope, vegetation) and stream (i.e., biofilm, organic matter, physical) predictors created patterns, and quantify the contribution of flow-connection to [DOC] variation in a boreal forest stream network. We included predictors in a statistical model which incorporated spatial autocorrelation due to flow-connection within stream networks. Together with model results, semi-variogram analysis suggested that kilometer-scale patches of varying DOC concentrations were created from spacing of tributaries and contrasting watershed effects on [DOC]. [DOC] was correlated with aspect, and highest concentrations were observed in streams draining north-facing slopes, likely due to flowpaths through organic soil overlying permafrost. Patches created by watershed variation were nested within a gradient of increasing [DOC] with drainage area, thus sources (e.g., production, watershed inputs) to downstream reaches outweighed sinks (e.g., remineralization). Strong autocorrelation among flow-connected sites indicated propagation of watershed and in-stream effects on [DOC] far downstream.

Christina Baker (POC,Primary Presenter), University of Alaska Fairbanks, clbaker5@alaska.edu;


Tamara Harms ( Co-Presenter/Co-Author), University of Alaska Fairbanks, tamara.harms@alaska.edu;


Jeremy Jones ( Co-Presenter/Co-Author), Univeristy of Alaska Fairbanks, jay.jones@alaska.edu;


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