SFS Annual Meeting

5/20/2019  |   11:00 - 11:15   |  250 AB

EXPLORING PLANKTONIC RESPIRATION USING SHORT-TERM IN SITU MEASUREMENTS Planktonic community respiration (CR) is a fundamental driver of aquatic processes including organic matter (OM) metabolism and mineralization, atmospheric gas exchange, and energy flow through food webs. Recent work suggests that CR may often be underestimated, in part because standard incubation approaches that track the loss of dissolved oxygen in the dark do not capture the rapid turnover of highly labile OM. Here we use novel short-term (<1hr) in situ protocols to demonstrate that CR may be grossly underestimated in the open-water zones of both freshwater and marine habitats, with non-linear rates of change over even short incubation periods. Further, we use these protocols to demonstrate higher than expected extents of both spatial and temporal variability within inland and tidally-influences coastal systems. We explore the connections between variability in CR and environmental conditions. Finally, we use a controlled experiment to explore connections between DO loss and short-term changes in labile OM processing within the water column. Such rapid cycling of OM by plankton is likely an important component of ecosystem functioning that warrants further investigation using instantaneous in situ approaches.

James Collins (Co-Presenter/Co-Author), University of Washington, james.r.collins@aya.yale.edu;


Angie Boysen (Co-Presenter/Co-Author), University of Washington, akboysen@gmail.com;


Kimberly Wickland (Co-Presenter/Co-Author), U.S. Geological Survey, kpwick@usgs.gov;


Steve Sadro (Co-Presenter/Co-Author), University of California, Davis, ssadro@ucdavis.edu;


Sarah Ellen Johnston (Co-Presenter/Co-Author), University of Lethbridge, sarah.johnston3@uleth.ca ;


Anitra Ingalls (Co-Presenter/Co-Author), University of Washington, aingalls@uw.edu;


Lisamarie Windham-Myers (Co-Presenter/Co-Author), U.S. Geological Survey, lwindham-myers@usgs.gov;


Brian Bergamaschi (Co-Presenter/Co-Author), U.S. Geological Survey, bbergama@usgs.gov;


Robert Striegl (Co-Presenter/Co-Author), USGS, rstriegl@usgs.gov;


Mark Dornblaser (Co-Presenter/Co-Author), USGS, mmdornbl@usgs.gov;


Robert Spencer (Co-Presenter/Co-Author), Florida State University, rgspencer@fsu.edu;


David Butman (Co-Presenter/Co-Author), University of Washington, dbutman@uw.edu;


Matthew Bogard (Primary Presenter/Author), University of Lethbridge, matthew.bogard@uleth.ca ;


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5/20/2019  |   11:15 - 11:30   |  250 AB

DENITRIFICATION IN A LARGE RIVER NETWORK OF MIXED LAND USE—A STRUCTURAL EQUATION MODELING ANALYSIS Land-use patterns and instream biogeochemistry processes affect loading rates of nitrogen from tributary rivers to the Great Lakes. Generally, loading rates are reasonably well documented, but land-use patterns and instream conditions that create biogeochemical hot spots for nitrogen processing and loss are less well understood on a broad scale. We evaluated instream nitrogen loss through measures of sediment denitrification and denitrification enzyme assay (DEA) rates at 110 sites distributed throughout the Fox River basin (16,400-km2 watershed) at baseflow conditions in August 2016. We developed a Structural Equation Model (SEM) to describe land use, sediment properties, and water column nitrogen availability that drive instream denitrification and DEA rates at base flow conditions. In August 2017, we resampled 50 of the 110 sites to validate the SEM model under baseflow conditions and in 2018 (May, June, August) we resampled 28 sites to assess the model extension to other flow conditions. Extension of the model to subsequent years and other flow conditions will be presented. The results provide additional information on the suite of factors that likely constrain instream biogeochemical cycling of nitrogen across a large river network

Lynn Bartsch (Primary Presenter/Author), U.S. Geological Survey, lbartsch@usgs.gov;


Rebecca Kreiling (Co-Presenter/Co-Author), U.S. Geological Survey, rkreiling@usgs.gov;


Victoria Christensen (Co-Presenter/Co-Author), U.S. Geological Survey, vglen@usgs.gov;


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5/20/2019  |   11:30 - 11:45   |  250 AB

SPATIAL HETEROGENEITY OF NITROGEN FIXATION AND DENITRIFICATION ACROSS A WETLAND-STREAM-LAKE INTERFACE Wetland – stream –lake interfaces are spatially heterogeneous and connected through cross-interface processes that alter material form and export across these ecosystems. Moreover, this heterogeneity may facilitate the co-occurrence of biogeochemical processes that are favored under incompatible environmental conditions, like N2 fixation and denitrification. We measured rates of N2 fixation and denitrification, along with a suite of environmental drivers, in 15 locations along 3 wetland-stream-lake interfaces of Lake Superior and northern Lake Huron. N2 fixation ranged from 0 – 1970 µg/m2/h, while denitrification ranged from 0-11500 µg/m2/h across all interfaces. N2 fixation occurred primarily in wetland sediment and on the macrophytes in streams and lakes, while denitrification occurred exclusively on sediments in all three habitats. Logistic regression showed organic matter content was an important predictor of the occurrence of denitrification (p = 0.04), but identified no significant models for N2 fixation. We will assess if microbial gene abundance is related to process rates and environmental drivers. Understanding the spatial complexity of biogeochemical processes is key for understanding how ecosystems respond to human and natural disturbance, which often simplifies and homogenizes habitats.

Erin Eberhard (Primary Presenter/Author), Kent State Univeristy , ekeberha@mtu.edu;


Amy Marcarelli (Co-Presenter/Co-Author), Michigan Technological University, ammarcar@mtu.edu;


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5/20/2019  |   11:45 - 12:00   |  250 AB

QUANTIFYING THE RECOVERY OF DENITRIFICATION FOLLOWING RESTORATION-RELATED CONSTRUCTION IN AN AGRICULTURAL WATERSHED In agricultural streams, floodplain restoration via the two-stage ditch has been shown to improve water quality. Constructed floodplains expand bioreactive surface area and enhance nitrate-N removal via microbial denitrification, thereby reducing export to downstream ecosystems. In the Shatto Ditch Watershed (IN), 0.8 km of two-stage were constructed at the watershed outlet in 2007. In 2017 and 2018, an additional 3.7 and 2.7 km were constructed moving upstream. We quantified recovery of denitrification following stream dredging and floodplain construction using experimental incubations of stream sediments and floodplain soils, measuring dinitrogen gas concentrations using membrane inlet mass spectrometry (MIMS). We measured denitrification on stream sediments upstream, which were higher before dredging (0.22 µgN/gDM/h), but were still comparable 3 weeks post-dredging (0.15 µgN/gDM/h). Nevertheless, stream sediment rates upstream remained low relative to sediments in the 2007 two-stage reach where sediments were never dredged (0.57 µgN/gDM/h). Our research suggests that stream sediments recolonize quickly post-dredging, on the order of weeks. In contrast, floodplains soils may take longer to recover with their intermittent hydraulic connectivity, which we are exploring with continued analyses. Lags in ecosystem function are important to consider when implementing any restoration-related construction.

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


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


Shannon Speir (Primary Presenter/Author), University of Arkansas, slspeir@uark.edu;


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5/20/2019  |   12:00 - 12:15   |  250 AB

AN INVESTIGATION OF LINKED ELEMENTAL CYCLES USING DUAL ISOTOPE EXPERIMENTS AND CONSTRAINT-BASED OPTIMIZATION MODELING Conceptualizing and modeling multiple interactive elemental cycles remains a challenge in the field of biogeochemistry, even at the scale of experimental mesocosms. Considering stoichiometric links among multiple elemental cycles is critical to predicting the outcomes from a broad spectrum of potentially relevant biogeochemical processes. Measuring and modeling multiple elemental cycles requires consideration of associated environmental signals, such as temporal variation in metabolite abundances and isotopic signatures. Here, we describe a combined experimental and modeling approach that leverages system constraints imposed by stoichiometry and thermodynamics in addition to time series datasets of both metabolite concentrations and stable isotope ratios. We present results from a set of mesocosm experiments in which carboys filled with stream water and gravel were amended with two stable isotope tracers (either ¹³C-enriched CH₃COONa and ¹⁵N-enriched NaNO₃ or ¹³C-enriched NaHCO₃ and ¹⁵N-enriched NH₄Cl). The carboy mesocosms were incubated in the dark with no headspace and sampled periodically for 7 days. We use a constraint-based optimization model generated by the Generalized Algorithm for Nutrient, Growth, Stoichiometric and Thermodynamic Analysis (GANGSTA) to posit the mechanisms by which dynamic interactions among elemental cycles emerge.

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


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


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


Joanna Blaszczak (Co-Presenter/Co-Author), University of Nevada, Reno, jblaszczak@unr.edu;


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


Elizabeth Mohr (Primary Presenter/Author), Montana State University, elizabethjmohr@gmail.com;


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5/20/2019  |   12:15 - 12:30   |  250 AB

WHOLE RIVER ESTIMATES OF DENITRIFICATION IN RESPONSE TO A LARGE-SCALE NITROGEN ENRICHMENT OF THE KANSAS RIVER (USA) Rivers play a critical role in transporting nutrients to coastal waters; thus, understanding river N transport and transformation is of fundamental importance. We asked: Does whole river denitrification change in response to a four-month addition of high nitrogen and enriched microbial community? We used a release of water from a decommissioned fertilizer plant (the former Farmland site, in Lawrence, KS) and its resident microbial enrichment culture into the Kansas River to address our question. We measured whole river denitrification rates using the open-channel estimate of di-nitrogen gas production from samples collected hourly (for 24 hours) at a pair of sites, 1.6 km upstream and 5.5 km downstream of the release point. We conducted the sampling at the end of the four-month release of the high nitrogen water and two weeks post-release. We paired whole-river estimates of denitrification with real-time nitrate and dissolved oxygen sensors, which measured concentrations on 15-min increments. Quantifying whether the Kansas River transports novel microbial communities and how riverine N cycling changes in response to the additions will aid us in understanding the connection between microbial communities and biogeochemical cycling in aquatic ecosystems.

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


Lydia Zeglin (Co-Presenter/Co-Author), Kansas State University, lzeglin@ksu.edu;


Matthew Nieland (Co-Presenter/Co-Author), Kansas State University, nielandm@k-state.edu;


Michelle Catherine Kelly (Co-Presenter/Co-Author), University of Kansas, michellekelly@ku.edu;


Janaye Hanschu (Co-Presenter/Co-Author), Kansas State University, jhanschu@ksu.edu;


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