6/05/2017  |   11:00 - 11:15   |  306B

BEYOND N AND P: TRACE METAL LIMITATION OF ALGAL PRODUCTION Algae require more than 20 different elements, yet the vast majority of what is known about nutrient limitation in stream ecosystems focuses on just N and P. Trace metals are required for electron transfer proteins used in photosynthesis and respiration and enzymes that catalyze N and P acquisition. Anthropogenic activity has altered elemental loading to stream ecosystems, however trace metal loading is frequently uncorrelated with N and P. The disconnect between nutrient and trace metal concentrations and dual requirements for metals and macronutrients within the same biochemical pathway suggests that low metal concentrations may limit nutrient uptake through co-limitation. We present data from streams in the Great Lakes basin that show potential trace metal limitation in both pristine and human-dominated watersheds. Furthermore, we used trace metal nutrient diffusing substrates (tNDS) with different combinations of elements to show that metal–nutrient co-limitation of algae was observed in >50% of study streams, and Zn–P co-limitation was common in streams low in dissolved inorganic P. We suggest that trace metals must be considered to fully resolve bottom-up drivers of stream primary production.

David Costello (Primary Presenter/Author), Kent State University, dcostel3@kent.edu;


Andrea Fitzgibbon ( Co-Presenter/Co-Author), Kent State University , afitzgib@kent.edu;


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6/05/2017  |   11:15 - 11:30   |  306B

CARBON... AND WHAT ELSE?: THE STOICHIOMETRY OF BROWNING IN LAKES OF NORTHERN WISCONSIN, USA Inputs of terrestrial dissolved organic matter (DOM) have increased substantially in many north temperate lakes. While this "browning" phenomena is often strictly associated with carbon, it likely also influences nutrient loading. In this paper, we characterize potential loads of carbon (C), nitrogen (N), and phosphorus (P) to seepage lakes in northern Wisconsin based on leachate source, watershed area, and shoreline development. Positive correlations between current C and N (R2=0.28, p<0.05) and P (R2=0.32, p<0.05) concentrations across lakes support allochthonous nutrient loading with DOM increases. We found that the molar C:N:P ratio was more P-rich in leaf leachates than soil leachates (leaves: 137:0.03:1, wetland soil: 185:7:1, forest soil: 459:31:1). Based on leachate stoichiometry and regional carbon budgets, we estimate that annual N and P fluxes to a lake could reach 900 and 300 kg, respectively. We constrain these fluxes using long-term records from regional seepage lakes that suggest, since 1984, browning has increased on average 4.6 Pt-Co yr-1 or 5.2 – 18.0 mg C L-1 (95% CI). Our results suggest that browning can have a substantial impact on lake stoichiometry and the ecological effects of this shift should be considered further.

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


Brittni Bertolet ( Co-Presenter/Co-Author), University of Notre Dame, brittnibertolet@gmail.com;


Nora Casson ( Co-Presenter/Co-Author), University of Winnipeg, n.casson@uwinnipeg.ca;


Stephen D. Sebestyen ( Co-Presenter/Co-Author), USDA Forest Service-Northern Research Station, ssebestyen@fs.fed.us;


Randy Kolka ( Co-Presenter/Co-Author), USDA Forest Service Northern Research Station, rkolka@fs.fed.us;


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


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6/05/2017  |   11:30 - 11:45   |  306B

DIFFERENTIAL RETENTION OF NITROGEN AND PHOSPHORUS IN LAKES As low points in the landscape, lakes integrate water and material from the surrounding landscape, and should be a reflection of their watersheds. However, lakes are variable in the stoichiometry of nitrogen (N) and phosphorus (P), even across lakes with similar watersheds. We hypothesized that variability in stoichiometry across lakes could be generated by internal, lake-specific differential retention of N and P. Nutrient retention for a given lake has been well-described by Vollenweider-type equations that show retention increases with residence time, but the underlying mechanisms and shapes of these relationships are different for N and P. An analysis of 710 lakes with published N and P budgets revealed that the most extreme lakes (shallow with short residence time, deep with long residence time) retained more N than P. However, most lakes (75%) retained more P than N, and median retention for P (38%) was nearly twice as high as N (20%). Landscape level patterns in lake stoichiometry may therefore be a function of both the chemical signatures of the surrounding landscape and lake-specific hydrology and morphology.

Samantha K Oliver (Primary Presenter/Author), University of Wisconsin Madison, skoliver@wisc.edu;


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


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6/05/2017  |   11:45 - 12:00   |  306B

RESPONSE OF A RESERVOIR ECOSYSTEM TO CHANGES IN WATERSHED AGRICULTURE OVER TWO DECADES: THE STOICHIOMETRY OF NUTRIENT INPUTS AND PHYTOPLANKTON NUTRIENT LIMITATION We present 23 years of data on the response of eutrophic Acton Lake to changes in watershed agriculture. Over the first decade, the use of conservation tillage increased greatly in the watershed. This led to large decreases in suspended sediment (SS) and P concentrations in inflow streams, and decreased (discharge-adjusted) loads of SS and P to the lake. However, during the second decade, stream SS changed little and soluble P actually increased. In contrast, stream nitrate changed little over the first decade, but declined sharply in the second decade. In Acton Lake, phytoplankton biomass increased markedly over the first decade, despite decreased inputs of P from streams, probably because declining lake SS concentrations alleviated phytoplankton light-limitation, and because of increasing biomass, and hence nutrient excretion, of detritivorous fish. Over the second decade, phytoplankton biomass showed no temporal trend. However, phytoplankton N-limitation became more common, whereas P was usually limiting in the first decade. This shift may reflect declining stream N:P ratios and a greater importance of internal loading, which has relatively low N:P. Our long-term data reveal complex, temporal scale-dependent responses of stoichiometry to changing watershed agriculture.

Michael Vanni (Primary Presenter/Author), Miami University, vannimj@miamioh.edu;


William Renwick ( Co-Presenter/Co-Author), Miami University, wrenwick@miamioh.edu;


Thomas Fisher ( Co-Presenter/Co-Author), Miami University, fishert4@miamioh.edu;


Emily Morris ( Co-Presenter/Co-Author), Miami University, morris55@miamioh.edu;


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6/05/2017  |   12:00 - 12:15   |  306B

LEAF LITTER BREAKDOWN IN LAKES: VARIABLE EFFECTS OF MACROINVERTEBRATES IN LAKES FROM ACROSS ONTARIO, CANADA Although considerable quantities of leaf detritus can be added to forested lakes, the processing of this material in lake ecosystems has received less study than that in streams and rivers. Here we assessed the role of macroinvertebrates in the breakdown of allochthonous plant detritus in lake ecosystems that vary in nutrients and temperature. We measured breakdown rates of trembling aspen leaves (Populus tremuloides) over 60-70 days in 16 lakes along a gradient of temperature and phosphorus concentrations located in four lake regions (Kawartha Highlands, Kawartha Lakes, Dorset Lakes, Experimental Lakes Area) of Ontario, Canada. We found substantial differences in leaf breakdown among regions with much faster rates seen in more nutrient-rich and warmer lakes. While macroinvertebrates increased decomposition rates, their effects were relatively small compared to those produced by regional differences in nutrients and temperature. While there were regional differences in detrital stoichiometry, we found little effect of lake nutrients or temperature on the ratios of released nutrients. Variable rates of leaf breakdown as shown here indicate that changes in lake trophic state, temperature and/or invertebrates all likely have significant effects on this important external carbon input in lakes ecosystems.

Sherri DeGasparro (Primary Presenter/Author), Trent University, Peterborough, Ontario, Canada, sherridegasparro@trentu.ca;


David Beresford ( Co-Presenter/Co-Author), Trent University, Peterborough, Ontario, Canada, davidberesford@trentu.ca;


Paul C. Frost ( Co-Presenter/Co-Author), Trent University, Peterborough, Ontario, Canada, paulfrost@trentu.ca;


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6/05/2017  |   12:15 - 12:30   |  306B

From elements to metabolism: exploring the coupling of autotrophic stoichiometry and ecosystem function in spring-fed rivers Whereas ecological stoichiometry is a framework based on elemental ratios for understanding how organisms interact within ecosystems; metabolism is an integrative metric of ecosystem function and energetics, synthesizing the relative contributions of multiple inputs, processes, and interactions. Relating the two may potentially inform ecosystem scale use of elements and energy. This study quantified the coupling between the stoichiometry of ecosystem metabolism, specifically the C:N ratios of integrated autotrophic assimilation, and the stoichiometric tissue ratios observed in the dominant autotrophs. Using high frequency in-situ nutrient sensors, the assimilatory fluxes of C and N in multiple spring-fed rivers of varying autotrophic species composition were estimated; additionally, autotroph cover in each spring river, body mass and tissue stoichiometry were measured. Results show strong correlation between measured tissue stoichiometry and elemental ratios at the ecosystem scale, suggesting that aggregated assimilatory fluxes may be useful for linking organismal nutrient content to the stoichiometry of ecosystem metabolism.

Rachel Nifong (Primary Presenter/Author), Agricultural Research Service, USDA, rachel.nifong@ars.usda.gov;


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