5/18/2015  |   13:30 - 13:45   |  102C

BIOGEOCHEMICAL REGIME SHIFTS IN COASTAL LANDSCCAPES: EFFECTS OF SALTWATER INTRUSION ON CARBON AND NITROGEN CYCLING IN A COASTAL PLAIN FRESHWATER WETLAND As a result of increasing drought frequency, soil oxidation, and rising sea levels, low lying coastal areas are increasingly subject to episodic and seasonal saltwater intrusion. Saltwater intrusion, which raises the pH and salinity of inland freshwaters and supplies high concentrations of base cations and sulfate, is expected to dramatically alter carbon and nitrogen in affected ecosystems. We performed marine salt experimental enrichments in the field and in a complementary controlled laboratory experiment with soil cores collected from the same large freshwater wetland complex in coastal North Carolina, USA. In both experiments saltwater enrichment significantly suppressed methane emissions and reduced methanogenesis potential for saturated sediments. Effects on nitrous oxide emissions were mixed, with saltwater enrichment reducing nitrous oxide emissions in the field but tending to enhance nitrous oxide emissions in the lab. Most surprising, in contrast to the majority of published research, we found that saltwater enrichment suppressed carbon mineralization and carbon dioxide emissions in the field and lab.

Ashley M. Helton (Primary Presenter/Author), University of Connecticut, amhelton@gmail.com;


Marcelo Ardon-Sayao (Co-Presenter/Co-Author), East Carolina University, ARDONSAYAOM@ecu.edu;


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

5/18/2015  |   13:45 - 14:00   |  102C

SEDIMENT MICROBIAL COMMUNITY COMPOSITION AND BIOGEOCHEMISTRY ALONG VERTICAL GRADIENTS IN A HIGH SULFUR SUBMERGED SINKHOLE IN LAKE HURON, MI Submerged groundwater seeps in Lake Huron establish ecosystems with distinctive geochemical conditions. In the low-O2, high-sulfur environment of the Middle Island Sinkhole (MIS), a 23-m deep seep, a metabolically flexible microbial mat capable of anoxygenic photosynthesis, oxygenic photosynthesis and chemosynthesis thrives. However, little is known about the structure and function of organic-rich sediments beneath the mat. Using parallel pore water and sediment geochemical characterization along with microbial community analysis, we elucidate relationships between microbial community structure and ecosystem function in a highly unique and environmentally vulnerable ecosystem along vertical gradients. Microbial community composition was distinctly different from non-groundwater affected areas at similar depth nearby in Lake Huron. MIS sediment communities changed with depth and were related to several geochemical variables, including organic matter, total sediment zinc, and multiple indicators of phosphorus availability, including pore water phosphate concentration, sediment total phosphorus, and sediment iron-to-phosphorus ratio. Despite the importance of high sulfur concentrations in the system, microbial community composition was unrelated to indicators of sulfur cycling, including pore water sulfate concentration and acid volatile sulfides.

Lauren Kinsman-Costello (Primary Presenter/Author), Kent State University, kinsmaniac@gmail.com;


Cody Sheik (Co-Presenter/Co-Author), University of Michigan, csheik@umich.edu;


G. Allen Burton (Co-Presenter/Co-Author), University of Michigan, burtonal@umich.edu;


Nathan Sheldon (Co-Presenter/Co-Author), University of Michigan, nsheldon@umich.edu;


Gregory Dick (Co-Presenter/Co-Author), University of Michigan, gdick@umich.edu;

5/18/2015  |   14:00 - 14:15   |  102C

SIMULATING CONCURRENT METABOLIC PATHWAYS IN BIOGEOCHEMICAL SYSTEMS The behavior of biogeochemical systems is dictated by interactions amongst multiple elemental cycles, yet elemental cycles are easier to conceptualize in isolation than in concert. To assist thinking in terms of biogeochemical systems rather than individual cycles, we developed a thermodynamically-based model that simulates the co-occurrence of competing metabolic pathways based on (1) the availability of electron donors and acceptors required by each pathway, (2) the energetic yield of each pathway, (3) the energetic demand of microorganisms, and (4) microbial growth constraints imposed by ecological stoichiometry. We performed a model sensitivity analysis by systematically varying the availability of DOC, oxygen, nitrate, sulfate, and methane in the model, and analyzed results with multivariate statistics to identify broad drivers of biogeochemical systems. Our results identify several hypotheses describing broad drivers of biogeochemical system behaviors, such as the implications of competition for electron donors versus acceptors and variation in the ratio of metabolic demand for energy versus free energy yield from potential metabolic pathways.

Ann Marie Reinhold (Primary Presenter/Author), Montana State University, Montana Institute on Ecosystems, reinhold@montana.edu;


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


Ashley M. Helton (Co-Presenter/Co-Author), University of Connecticut, amhelton@gmail.com;


Robert Payn (Co-Presenter/Co-Author), Montana State University, Montana Institute on Ecosystems, rpayn@montana.edu;


Clemente Izurieta (Co-Presenter/Co-Author), Montana State University, Montana Institute on Ecosystems, clemente.izurieta@cs.montana.edu;


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


Amy Burgin (Co-Presenter/Co-Author), University of Kansas, burginam@ku.edu;

5/18/2015  |   14:15 - 14:30   |  102C

HYDROLOGIC CONTROLS ON BIOGEOCHEMICAL GRADIENTS IN THICK LAYERS OF FLOCCULENT ORGANIC SEDIMENTS IN A THROUGH-FLOW WETLAND Thick accumulations of flocculent organic sediment, or floc, are nearly ubiquitous in shallow freshwater ecosystems lacking strong physical disturbance regimes. Despite the prevalence of these sediments in a diversity of shallow water bodies, there is little information on their biogeochemical and ecological importance. Importantly, floc forms a transitional zone that is more connected to overlying water than relatively consolidated sediments, and is subject to dynamic variation in reduction-oxidation (redox) status. In Fall 2014, we monitored heat-exchange processes across the floc-water interface using vertical fiber-optic high-resolution distributed temperature sensors (HRTS) to reveal the timing and modes of hydrologic exchange (i.e., conduction vs. advection dominated) in thick floc layers (e.g. up to 1 m) of a through-flow wetland. The profiles revealed discrete zones of floc influenced by groundwater upwelling that limited vertical heat and solute exchange from surface waters, while other profiles showed deeper exchange patterns. The vertical porewater chemical profiles collected adjacent to each HRTS showed diel changes in redox sensitive solutes along the shallow profiles. This presentation explores how dominant hydrologic exchange processes influence biogeochemical gradients in floc.

Dustin Kincaid (Primary Presenter/Author), W.K. Kellogg Biological Station and Department of Integrative Biology, Michigan State University, kincai32@msu.edu;


Martin Briggs (Co-Presenter/Co-Author), U. S. Geological Survey, Hydrogeophysics Branch, Storrs, Connecticut, USA, mbriggs@usgs.gov;


Stephen K. Hamilton (Co-Presenter/Co-Author), Michigan State University & Cary Institute of Ecosystem Studies, hamilton@kbs.msu.edu;


Jay Zarnetske (Co-Presenter/Co-Author), Department of Earth and Environmental Sciences, Michigan State University, jpz@msu.edu;

5/18/2015  |   14:30 - 14:45   |  102C

DEVELOPING A REGIONAL TO CONTINENTAL SCALE MODEL OF DISSOLVED ORGANIC CARBON FLUX AND PROCESSING IN RIVER NETWORKS Dissolved organic carbon (DOC) is an important energy source influencing stream ecosystem function and also has implications for drinking water supply. Though there are currently several models of catchment scale DOC dynamics, there is no model simulating DOC dynamics in river networks at the regional to continental scale. We have developed such a model for the northeastern US, using the Framework for Aquatic Modeling in the Earth System (FrAMES), a process based and spatially distributed hydrology and biogeochemistry model. We compared model performance predicting DOC inputs to the river system using empirical loading relationships based on wetlands or soil type with runoff and utilizing output from an existing terrestrial ecosystem model (TEM). We applied DOC removal rates based on a literature review of reach scale DOC uptake measurements. Applying uptake velocities from reach-scale additions of simple compounds or leachates resulted in an apparent overestimation of processing rates and underestimation of DOC concentrations. Advancement of river network DOC models will necessitate empirical research to provide additional information regarding in-situ processing rates of ambient DOC and mechanisms controlling DOC loading to streams.

Madeleine Mineau (Primary Presenter/Author), University of New Hampshire, m.m.mineau@unh.edu;


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


Robert Stewart (Co-Presenter/Co-Author), University of New Hampshire, rob.stewart@unh.edu;


Christopher Hunt (Co-Presenter/Co-Author), University of New Hampshire, chunt@unh.edu;


David Kicklighter (Co-Presenter/Co-Author), Marine Biological Laboratory, dkicklighter@mbl.edu;