SFS Annual Meeting

6/05/2024  |   13:30 - 13:45   |  Independence Ballroom D

EFFECTS OF SNOWPACK PERSISTENCE ON DISSOLVED ORGANIC CARBON FLUXES FROM WATERSHEDS Spring snowmelt pulses are important annual events in poleward temperate regions that exert a strong influence on organic carbon resource dynamics and energy fluxes. The duration, coverage, and persistence of temperate region snowpack change as the climate warms and winter rain events increase. We explore how dynamic snowpack characteristics can impart changes in watershed dissolved organic carbon (DOC) source dynamics and instream processes, along with hydrologic transport mechanisms and solute reactions, using concentration-discharge (cQ) relationships and measures of hillslope-stream connectivity. Our study compares years with continuous snowpack to those with intermittent snowpack (multiple total snowpack thaw events) over the winter season to assess the influence on stream DOC fluxes using a 30-year record from headwatersheds in New Hampshire, U.S.A. Our results indicate that the proportion of precipitation as rain in December and January has been increasing over the record, driving anomalous high DOC pulses out of the watershed in early winter. We classify results based on multiple metrics of hydrologic change, including baseflow separation and diel and annual temperature signal relations, to broadly classify groundwater contribution vs. runoff/quickflow to explore variations in transport export dynamics between watershed aspects and snowpack variability. Our study examines how these watershed classifications align with cQ relationships over varied winter snowpack regimes to evaluate variability in winter DOC export patterns and underlying changes in source and transport mechanisms.

Danielle Hare (Primary Presenter/Author), Cary Institute of Ecosystem Studies, hared@caryinstitute.org;

Chris Solomon (Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, solomonc@caryinstitute.org;

Geoff Wilson (Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, wilsong@caryinstitute.org ;

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

Tammy Wooster (Co-Presenter/Co-Author), Cary Institute of Ecosystem Studies, woostert@caryinstitute.org;

Mark Green (Co-Presenter/Co-Author), Case Western Reserve University, mbg78@case.edu;

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6/05/2024  |   13:45 - 14:00   |  Independence Ballroom D

The gas they passed: carbon costs of dam removal from large reservoirs By prolonging residence times and concentrating organic matter in oxygen-depleted environments, dams can facilitate high carbon dioxide and methane emissions from their reservoirs. Reduced emissions have been proposed as a benefit of dam removal; however, the impact of removal on carbon balance depends on several pathways of gas exchange. For example, reservoir drawdown can expose organic matter previously buried in sediments to rapid mineralization, resulting in a ‘burp’ of carbon emissions upon removal, but regrowing vegetation in the reservoir footprint can sequester carbon. We combined literature values, statistical, and mechanistic models to estimate carbon balance before, during, and after removal for the Glines Canyon (Elwha River, WA) and Veazie Dams (Penobscot River, ME). We find that before removal both dams had low surface emissions. The Glines Canyon reservoir was a large net sink for carbon dioxide-equivalents (-11600 (95% CI: -33400, -2470) Mg/yr) and the Veazie reservoir was a small source (54 (-245, 114) Mg/yr). During removal, the Glines Canyon footprint ‘burped’ the equivalent of 16 years of pre-removal burial and the Veazie ‘burped’ 7.5 years of pre-removal emissions. After removal, the Glines Canyon footprint became a smaller sink (-479 (-694, 1110) Mg/yr) and the Veazie became a larger source of emissions (5170 (495, 24000) Mg/yr) integrated over 100 years. These results suggest that the impact of dam removals on carbon balance can vary substantially among dams, for which the amount of buried sediment and its fate upon dam removal may be key determinants.

Laura Naslund (Primary Presenter/Author), University of Georgia, laura.naslund@uga.edu;

Andrew S. Mehring (Co-Presenter/Co-Author), University of Louisville, andrew.mehring@louisville.edu;

Amy Rosemond (Co-Presenter/Co-Author), University of Georgia, rosemond@uga.edu;

Kyle McKay (Co-Presenter/Co-Author), Environmental Laboratory, U.S. Army Engineer Research and Development Center, kyle.mckay@usace.army.mil;

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

Seth Wenger (Co-Presenter/Co-Author), Odum School of Ecology, University of Georgia, swenger@uga.edu;

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6/05/2024  |   14:00 - 14:15   |  Independence Ballroom D

CHASING CARBON: USING SMART TRACERS TO EVALUATE ORGANIC MATTER STORAGE, TRANSFORMATION, AND TRANSPORT IN A FORESTED HEADWATER STREAM Stream networks act as dynamic reactors, where flow is a predominant control on the fate of carbon (C) at the watershed-scale. Riverine C fluxes exist along a storage-transport-transformation continuum, largely as dissolved and fine particulate organic matter (DOM<0.7µm and 0.7µm
Michelle Wolford (Primary Presenter/Author), University of Alabama, mawolford@crimson.ua.edu;

Arial Shogren (Co-Presenter/Co-Author), University of Alabama, ashogren@ua.edu;

Carla L. Atkinson (Co-Presenter/Co-Author), The University of Alabama, carla.l.atkinson@ua.edu;

Shang Gao (Co-Presenter/Co-Author), University of Arizona, shanggao@arizona.edu;

Erin Hotchkiss (Co-Presenter/Co-Author), Virginia Polytechnic Institute and State University (Virginia Tech), ehotchkiss@vt.edu;

Stephen Plont (Co-Presenter/Co-Author), The University of Alabama, plontste@gmail.com;

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6/05/2024  |   14:15 - 14:30   |  Independence Ballroom D

SPATIAL AND TEMPORAL CONTROLS ON ORGANIC-MATTER DECOMPOSITION IN A MIXED LAND USE WATERSHED East Fork Poplar Creek (EFPC) in East Tennessee, USA, drains 77 km2, mixed land-use watershed. The first-order stream drains primarily industrial and urban land, and land cover then transitions to rural and forest further downstream. We measured organic-matter decomposition rates using cotton strips bimonthly for one year at 10 mainstem sites (from 1st to 4th-order) and at 4 tributary sites throughout EFPC watershed. Our objective was to examine spatial and temporal controls on organic-matter decomposition in this heterogeneous watershed. Preliminary data analysis suggests that there was strong seasonality in organic-matter decomposition rates, primarily driven by water temperature. When decomposition rates were expressed per degree day, additional drivers were revealed, including a negative relationship with pH and a positive relationship with nitrate concentrations. A spatial pattern in organic-matter decomposition was less apparent, but decomposition rates in the mainstem were generally higher than in the tributaries. Interestingly, the lowest decomposition rates were measured in a tributary draining a predominantly urban subwatershed and in a tributary draining a predominantly forested subwatershed. Further analyses will evaluate synchrony/asynchrony in organic-matter decomposition rates and associated drivers with an overall goal of advancing predictive understanding of the dominant processes controlling watershed biogeochemistry.

Natalie Griffiths (Primary Presenter/Author), Oak Ridge National Laboratory, griffithsna@ornl.gov;

Marie J. Kurz (Co-Presenter/Co-Author), Oak Ridge National Laboratory , kurzmj@ornl.gov;

Scott Tiegs (Co-Presenter/Co-Author), Oakland University, tiegs@oakland.edu;

Matthew Berens (Co-Presenter/Co-Author), Oak Ridge National Laboratory, berensmj@ornl.gov;

Scott Brooks (Co-Presenter/Co-Author), Oak Ridge National Laboratory, brookssc@ornl.gov;

Elizabeth Herndon (Co-Presenter/Co-Author), Oak Ridge National Laboratory, herndonem@ornl.gov;

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6/05/2024  |   14:30 - 14:45   |  Independence Ballroom D

Urbanization alters dissolved organic matter and microbial nutrient acquisition in subtropical urban streams (Georgia, USA) Dissolved organic matter (DOM) is an important energy source for aquatic microbes, which can reshape ecosystem structures and functions. Aquatic microbes are usually carbon- or nutrient-limited (or co-limited), and several enzymes have been identified as critical mediators in regulating carbon (C), nitrogen (N) and phosphorus (P) cycling. Yet, urbanization can significantly change the amount, sources, composition, and lability of DOM in stream water. Little is known about how urban heterogeneity influences the riverine DOM with the consequences of microbial function in the water column. We evaluate the effects of hydroclimatic drivers, land use/land cover, and a suite of urban infrastructure and demographic information on the availability of riverine DOM, inorganic nutrients, and extracellular enzyme activity in metropolitan Atlanta, GA. Data were obtained from, four seasonal synoptic sampling campaigns in 20 streams in 2021–2022. Our preliminary results indicate that bioavailable, autochthonous DOM (algal or microbial sources) increases along the gradient of urban land use, which is stimulated by dissolved inorganic nitrogen from point and/or nonpoint sources (e.g., impervious surfaces and wastewater inputs). The ratios of ?-glucosidase (BG, potential C acquiring enzyme) to leucine aminopeptidase (LAP, potential N acquiring enzyme) activity and BG to alkaline phosphatase (AP, potential P acquiring enzyme) activity approach 1:1 with decreasing autochthonous DOM, suggesting nitrogen and and phosphorus co-limitation in urban streams may constrain organic carbon remineralization and microbial metabolism when bioavailable C resources increase. Our study provides new insights to understand complex relationships between microbial nutrients and carbon acquisition in urban watersheds.

Shuo Chen (Primary Presenter/Author), University of Georgia; University of Florida, schen83@crimson.ua.edu;

Krista Capps (Co-Presenter/Co-Author), University of Georgia, kcapps@uga.edu;

Rebecca Hale (Co-Presenter/Co-Author), Smithsonian Environmental Research Center, haler@si.edu;

Jennifer Follstad Shah (Co-Presenter/Co-Author), University of Utah, jennifer.shah@envst.utah.edu;

Kristina Hopkins (Co-Presenter/Co-Author), U.S. Geological Survey, khopkins@usgs.gov;

Liz Ortiz (Co-Presenter/Co-Author), Florida International University, lorti080@fiu.edu;

Jacob Rudolph (Co-Presenter/Co-Author), Smithsonian Environmental Research Center, rudolphjc@icloud.com;

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6/05/2024  |   14:45 - 15:00   |  Independence Ballroom D

ENVIRONMENTAL FACTORS HAVE STRONGER IMPACTS THAN FRESHWATER MUSSELS ON BENTHIC NITROGEN FLUXES. Animal effects on ecosystem function are governed by functional traits that mediate their interactions with the environment. Freshwater mussels are a functionally diverse group of filter-feeding bivalves that can influence biogeochemical processes such as sediment N2-fluxes, by ingesting, transforming, and translocating suspended nutrients into the benthos via excretion and biodeposition. We conducted a field experiment to test whether mussels with contrasting functional traits—specifically soft-tissue stoichiometry—had differing effects on sediment N2-fluxes. We predicted that: 1) mussels would stimulate N2-flux rates over controls; 2) high C:N species would stimulate N2-fluxes over low C:N species by excreting and egesting more bioavailable N. We performed a series of light-dark metabolism incubations in water-tight incubation chambers. We took serial water samples to quantify N2-fluxes and sediment cores to quantify potential denitrification (DNF) and anammox rates. Across treatments, N2-flux rates increased in the dark and decreased in the light - suggesting autotrophic N-fixation. Neither N2-fluxes, nor potential DNF and anammox rates changed with species treatments. Our findings suggest that light affects biogeochemical processes by stimulating N-uptake by benthic autotrophs. Short incubation periods or prevailing environmental factors may explain the limited influence of mussels on N2-fluxes and potential DNF and anammox rates observed in this study. Our findings emphasize the importance of environmental factors in shaping the animal-mediated influences on ecosystem function.

Matthew Lodato (Primary Presenter/Author), University of Alabama, matthew.lodato5592@gmail.com;

Jonathan Lopez (Co-Presenter/Co-Author), The University of Alabama, jwlopez@ua.edu;

Taylor Ledford (Co-Presenter/Co-Author), Smithsonian , tledford@crimson.ua.edu;

Carla L. Atkinson (Co-Presenter/Co-Author), The University of Alabama, carla.l.atkinson@ua.edu;

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