SFS Annual Meeting

5/22/2018  |   14:00 - 14:15   |  321

LAND USE RESPONSES AND SEASONAL ADAPTATION OF WHOLE-STREAM METABOLISM AND NITRATE UPTAKE REVEALED BY HIGH-FREQUENCY, IN-SITU SENSORS Stoichiometric constraints imply that the cycling of carbon and other essential nutrients are closely coupled in space and time in stream ecosystems. Rates of cycling and their driving processes are affected by numerous environmental variables (e.g., temperature and light) and may be modified by land use and land cover. In this study, we used a combination of in-situ¬ sensor technologies to estimate gross ecosystem production (GEP), ecosystem respiration (ER), and nitrate uptake (NU) in streams draining three watersheds with different dominant land uses: forested, agricultural, and urban. GEP and ER differed significantly among watersheds and within seasons, following patterns in light and nutrient availability. We observed seasonal patterns in metabolic sub-parameters (alpha, Pmax) that may reflect community-scale algal succession or adaption. We calculated NU based on diurnal fluctuations in dissolved nitrate concentrations measured continuously by in-situ spectrophotometers. NU was significantly correlated with GEP, especially in the most productive stream (urban). The NU was higher than expected based on GEP and simple (Redfield) stoichiometric considerations. When potential rates of denitrification were considered, the ratio of NU and GEP were in better alignment.

William Breck Bowden (Primary Presenter/Author), University of Vermont, breck.bowden@uvm.edu;


Matthew Vaughan (Co-Presenter/Co-Author), Lake Champlain Basin Program, mvaughan@lcbp.org;


Ryan Sleeper (Co-Presenter/Co-Author), University of Vermont, rsleeper@uvm.edu;


Andrew Schroth (Co-Presenter/Co-Author), University of Vermont, aschroth@uvm.edu;


Presentation:
This presentation has not yet been uploaded.

5/22/2018  |   14:15 - 14:30   |  321

THE INFLUENCE OF BIOLOGICAL NITROGEN TRANSFORMATIONS ON LAKE PRODUCTIVITY: AN ANALYSIS USING LARGE-SCALE ECOLOGICAL STOICHIOMETRY We apply a simple stoichiometric model to characterize nitrogen (N) surpluses and deficits in lakes relative to P, and how biological N transformations relate to stoichiometry. Using the US EPA National Lakes Assessment database and other published data (n = 1970 lakes), the model showed that the proportion of lakes with a N surplus decreased with increasing chl-a concentrations. Sixty-seven percent of lakes had a N deficit relative to P when a stoichiometric boundary for N deficiency included N+P co-limitation (N:P < 23 by mass), and these lakes were losing reactive N relative to P due to net denitrification. Alternatively, 14% of lakes had a N surplus and were also losing reactive N due to net denitrification. Finally, 19% of lakes had a N surplus and were gaining N due to net N2 fixation, but these lakes represented the most unproductive lakes in the database (mean chl-a = 6 µg/L). These results indicate that, rather than ‘evolving’ P limitation, N transformations are dominated by N sinks (i.e., denitrification), which perpetuates N+P co-limitation, and even strict N limitation in some lakes.

Thad Scott (Primary Presenter/Author), Baylor University, Thad_Scott@baylor.edu ;


Mark McCarthy (Co-Presenter/Co-Author), Wright State University, mjm.kingston@gmail.com;


Hans Paerl (Co-Presenter/Co-Author), UNC Chapel Hill Institute of Marine Sciences, Hans_Paerl@unc.edu;


Presentation:
This presentation has not yet been uploaded.

5/22/2018  |   14:30 - 14:45   |  321

LONG-TERM LAKE RECORDS REVEAL DECOUPLING OF NITROGEN AND PHOSPHORUS CYCLES IN RESPONSE TO AN EXTREME RAINFALL EVENT The ecosystem impacts of precipitation events on lakes are related to both the magnitude of the event and the internal cycling processes within the lake when the event occurs. In this paper, we combine discharge records with long-term lake water quality datasets to investigate the impacts of extreme events on nitrogen and phosphorus cycling in Lake Mendota, a large lake in an urban and agricultural watershed. In June 2008, precipitation totals in the watershed were 400% above normal values, triggering the largest discharge event recorded during 40 years of monitoring. Following the extreme event, the lake-wide mass of nitrogen and phosphorus increased by 35% and 21%, respectively (based on records between 1995 – 2015). Nitrogen concentrations remained elevated longer than phosphorus, suggesting (1) that nitrogen inputs were sustained longer than phosphorus and/or (2) that in-lake biogeochemical processing was more efficient at removing phosphorus compared to nitrogen. Surficial N:P ratios remained elevated after the storm at least seven years. As climate change is expected to increase extreme event frequency, continued ecosystem monitoring is needed to understand how these biogeochemical responses may translate to water quality concerns.

Jessica Corman (Primary Presenter/Author), University of Nebraska - Lincoln, jesscorman@gmail.com;


Luke Loken (Co-Presenter/Co-Author), University of Wisconsin-Madison, lloken@wisc.edu;


Samantha Oliver (Co-Presenter/Co-Author), United States Geological Survey, oliver.samanthak@gmail.com ;


Sarah Collins (Co-Presenter/Co-Author), University of Wisconsin-Madison, scollins23@wisc.edu ;


Hilary Dugan (Co-Presenter/Co-Author), University of Wisconsin-Madison, hdugan@wisc.edu;


Emily Stanley (Co-Presenter/Co-Author), University of Wisconsin - Madison, ehstanley@wisc.edu;


Presentation:
This presentation has not yet been uploaded.

5/22/2018  |   14:45 - 15:00   |  321

NITROGEN TO PHOSPHORUS RATIO AS A DRIVER OF ARSENIC RETENTION Arsenic (As), a toxic trace element, can be taken into cells in place of phosphorus (P) and decouple phosphorylation, hindering energy production. Organisms take up more As when P is low, and our research shows that microbial As uptake depends on relative nitrogen (N:P), not just P concentration alone. However, the effects on higher trophic levels of increased As uptake resulting from variation in background N:P are unknown. Here, we evaluate if the N:P stoichiometry of a stream and its effects on processes associated with trophic exchanges control the retention and transport of As in geothermal streams, which are naturally rich in As. We measured food web As and invertebrate As excretion in three geothermal streams and three corresponding non-geothermal streams, all with varying N:Ps. Invertebrate P excretion was greater in As-rich geothermal streams than non-geothermal streams, and As and P excretion were both higher in low N:P (N-limited) streams; both results indicate that invertebrate excretory mechanisms may fail to distinguish between As and P and support our hypothesis that N:P drives As retention and transport in stream food webs.

Sarah Collins (Co-Presenter/Co-Author), University of Wisconsin-Madison, scollins23@wisc.edu ;


Andrea C. Encalada (Co-Presenter/Co-Author), Instituto BIOSFERA, Universidad San Francisco de Quito, Cumbayá, Ecuador Biológicas y Ambientales, Universidad San Francisco de Quito, Cumbaya, Ecuador, aencalada@usfq.edu.ec;


Helena Guasch (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), Spain, helena.guasch@ceab.csic.es;


Murray McBride (Co-Presenter/Co-Author), Cornell University, mbm7@cornell.edu;


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


Steven Thomas (Co-Presenter/Co-Author), University of Alabama, sathomas16@ua.edu;


Alexander Flecker (Co-Presenter/Co-Author), Cornell University, Ithaca, NY, USA, asf3@cornell.edu;


Keeley MacNeill (Primary Presenter/Author), Oregon State University, keeleymacneill@gmail.com;


Presentation:
This presentation has not yet been uploaded.

5/22/2018  |   15:00 - 15:15   |  321

THE EFFECTS OF NUTRIENT LIMITATION ON THE TEMPORAL COUPLING OF NUTRIENT UPTAKE Theory predicts that under nutrient replete conditions, nutrient uptake will occur only during photosynthesis, whereas under nutrient limitation, this uptake will occur during both day and the night equally, becoming decoupled from carbon uptake. To test this experimentally, we inoculated 20 experimental streams with biofilm-covered rocks and manipulated nutrient loading such that some streams were limited by nutrients, and others were not. We measured uptake over 24 hour periods and compared day and night uptake with GPP (photosynthesis). In the high nutrient streams, we observed day-night uptake differences that increased with GPP, whereas in the low nutrient streams, there was little to no observed difference between day and night uptake rates. The shift between these two behaviors occurs over a narrow concentration window, while other potential indicators of nutrient limitation such as GPP did not display such a strong division between high and low nutrient conditions. Diel variation in nutrient concentration may therefore serve as a useful diagnostic of nutrient limitation status.

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


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


Jim Heffernan (Co-Presenter/Co-Author), Duke University, james.heffernan@duke.edu;


Catherine Chamberlin (Primary Presenter/Author), Duke University, catherine.chamberlin@duke.edu;


Presentation:
This presentation has not yet been uploaded.

5/22/2018  |   15:15 - 15:30   |  321

INTERACTIVE EFFECTS OF TEMPERATURE AND NUTRIENTS ON STREAM BIOFILM STRUCTURE AND FUNCTION The interactive effects of climate warming and eutrophication are poorly understood. In particular, we lack understanding of how the quantity and stoichiometry of nutrient supply shapes ecosystem responses to warming. We conducted three successive stream-side channel experiments in the southwestern region of Iceland that manipulated water temperature (8°C-25°C) as well as nitrogen (N; 0-200 ug/L) and phosphorus (P; 0-200 ug/L) supplies and ratios (N:P; 0.02-40 M). On the basis of previous research, we predicted that N supply rate and N:P stoichiometry would control biofilm assemblage structure, N₂-fixation rates, and gross primary production (GPP). We found that N₂-fixation increased with temperature (71-fold over the experimental temperature range), decreased with N supply rate (44-fold over the N treatment gradient), and shaped the temperature dependence of GPP. Surprisingly, P supply and N:P ratio did not influence N₂-fixation or ecosystem metabolism, suggesting that P supply was not limiting in this system even at high N supply rates and ratios. Our results highlight the importance of considering both nutrient supply rates and ratios, as well as limiting conditions, when predicting ecosystem responses to warming.

Lyndsie Collis (Primary Presenter/Author), The Ohio State University, collis.21@buckeyemail.osu.edu;


Jonathan P. Benstead (Co-Presenter/Co-Author), The University of Alabama, jbenstead@ua.edu;


Wyatt Cross (Co-Presenter/Co-Author), Montana State University, wyatt.cross@montana.edu ;


Paula Furey (Co-Presenter/Co-Author), St. Catherine University, pcfurey@stkate.edu;


Gisli Mar Gislason (Co-Presenter/Co-Author), University of Iceland, gmg@hi.is;


Alexander D Huryn (Co-Presenter/Co-Author), The University of Alabama, huryn@bama.ua.edu;


Philip Johnson (Co-Presenter/Co-Author), University of Alabama, pjohnson@eng.ua.edu;


Jon S Olafsson (Co-Presenter/Co-Author), Icelandic Marine and Freshwater Research Institute, jon.s.olafsson@gmail.com;


Delorianne Sander (Co-Presenter/Co-Author), St.Catherine University, drsander12@gmail.com;


Jill Welter (Co-Presenter/Co-Author), St. Catherine University, jill.welter@gmail.com;


James Hood (Co-Presenter/Co-Author), The Ohio State University, hood.211@osu.edu;


Presentation:
This presentation has not yet been uploaded.