6/05/2017  |   09:00 - 09:15   |  306A

EFFECTS OF PHOSPHORUS AND LIGHT ON RECALCITRANT ORGANIC MATTER DEGRADATION IN LOTIC SYSTEMS Light may increase algal growth and labile organic matter (LOM) production that can stimulate recalcitrant organic matter (ROM) decomposition. This priming effect (PE) may be more important under low nutrient concentrations. We tested whether phosphorus (P) concentrations (10, 100, 500 ?g P/L) and light [full (100%) or shade (19% of full light)] interact to affect ROM decomposition suggesting the PE, which is the difference between full light and shaded treatments, is greater at low nutrient concentrations using experimental recirculating mesocosms. Time and light interacted significantly to drive suspended algal biomass increases (p=0.009) and P was not statistically significant. Time, light, and P interacted significantly to drive periphyton increases (p=0.038). Under low to moderate nutrients there was positive PE, but under high nutrients negative PE was observed. Light and P interacted significantly to decrease leaf litter fiber mass (p=0.003), increase fiber % (p=<0.001), decrease lignin-specific mass in low to moderate nutrients and increase in high nutrients (p=0.002), and increase lignin-specific % (p=<0.001). Our research supports the hypothesis that magnitude and direction of PE depends on dissolved nutrient availability in aquatic ecosystems.

Brooke Howard-Parker (Primary Presenter/Author), University of Arkansas, bbhowardparker@gmail.com;


Brendon White ( Co-Presenter/Co-Author), University of Arkansas, blw023@email.uark.edu;


Michelle Evans-White ( Co-Presenter/Co-Author), University of Arkansas, mevanswh@uark.edu;


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6/05/2017  |   09:15 - 09:30   |  306A

COMPARING LEAF BREAKDOWN AND MACROINVERTEBRATE ASSEMBLAGES AMONG THREE COASTAL PLAIN RIVERS We compared leaf breakdown and macroinvertebrate assemblages in main-channel habitats of three Coastal Plain rivers in southeast Georgia. Over two seasons (fall 2014 and spring 2015), a total of 192 coarse-mesh packs of water oak (Quercus nigra) leaves were retrieved across six study sites (two per basin) to assess the effects of flow regime, particularly discharge, on breakdown rates and assemblage structure. Despite significant differences in discharge during the fall (p = 0.0013), each basin exhibited similar processing coefficients (avg. k = -0.013/d). Significant differences in discharge were also observed during the spring (p = 0.0015), but processing coefficients remained similar among basins (avg. k = -0.011/d). Fall assemblages were similar among basins based on abundance (p = 0.121) and biomass (p = 0.091). Spring assemblages were also similar among basins based on abundance (p = 0.056) and biomass (p = 0.071). These results suggest that discharge is not a determining factor in leaf breakdown rates and reinforce the usefulness of the ecoregion concept in delineating macroinvertebrate distributions in these systems.

V. Byron Collins (Primary Presenter/Author), Georgia Southern University , vc00812@georgiasouthern.edu;


Checo Colon-Gaud ( Co-Presenter/Co-Author), Georgia Southern University, jccolongaud@georgiasouthern.edu;


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6/05/2017  |   09:30 - 09:45   |  306A

PATTERNS OF MACROINVERTEBRATE DIVERSITY ASSOCIATED WITH PERIPHYTIC ALGAE ON LEAF DEBRIS UNDER CONTRASTING LIGHT AND NUTRIENT CONDITIONS Forested temperate headwater streams are supported energetically by the breakdown of leaf debris by heterotrophic microbes and macroinvertebrate shredders. Recent work, however, has indicated algae on leaf debris may contribute to leaf breakdown and shredder nutrition. It is therefore likely that leaf-associated algae may be involved in other aspects of trophic dynamics in headwater streams. We performed a manipulative light experiment in six streams (three low and three high nutrient concentrations) by exposing red maple leaf packs (Acer rubrum) to either ambient or shaded light conditions for four weeks (n=5/light treatment/stream) in winter 2017 to examine the relationship between macroinvertebrate diversity and algal colonization. Macroinvertebrate functional and taxonomic diversity, algal biomass (chlorophyll-a), and leaf stoichiometry (C:N:P) were measured for each leaf pack. Chlorophyll-a averaged (±SE) 0.79±0.29, 0.31±0.05, 1.74±0.54, and 0.65±0.26 mg/m² on low nutrient-ambient, low nutrient-shaded, high nutrient-ambient, and high nutrient-shaded leaf packs, respectively. Results regarding macroinvertebrate diversity in relation to algal biomass will be discussed.

Rebecca Eckert (Primary Presenter/Author), University of Maryland, reckert@umd.edu;


William Lamp ( Co-Presenter/Co-Author), University of Maryland, lamp@umd.edu;


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6/05/2017  |   09:45 - 10:00   |  306A

Annual patterns in aquatic metabolism and CO2 emissions from New Hampshire streams Recent evidence has highlighted the ubiquity of carbon dioxide (CO₂) supersaturation in streams, yet our understanding of how the source of CO₂ (aquatic production versus catchment sources) varies in time and across different aquatic systems remains limited. Here we report two years of daily stream gross primary production (GPP), ecosystem respiration (ER), and CO₂ emissions estimates across five New Hampshire streams that vary in size, nutrient loading, and landscape context. All streams were net heterotrophic, with predictable seasonal peaks in GPP and ER. The estimated contribution of aquatic net ecosystem production (NEP) to stream CO₂ emissions varied from approximately 0 – 75%, although these estimates were sensitive to small changes in NEP for some sites. The proportion of CO₂ emissions supported by aquatic NEP was lower at higher discharge, perhaps due to increased CO₂ transport from soils to streams during wetter periods, or to biomass removal by scouring flows. Catchment sources represent substantial contributions to CO₂ emissions from temperate streams, but the proportion of CO₂ emissions from in situ carbon transformation is variable throughout the growing season.

Lauren Koenig (Primary Presenter/Author), University of New Hampshire, lauren.koenig@unh.edu;


Lisle Snyder ( Co-Presenter/Co-Author), University of New Hampshire, lisle.snyder@unh.edu;


Alison Appling ( Co-Presenter/Co-Author), US Geological Survey, alison.appling@gmail.com;


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


Jody Potter ( Co-Presenter/Co-Author), University of New Hampshire, jody.potter@unh.edu;


William H McDowell ( Co-Presenter/Co-Author), University of New Hampshire, bill.mcdowell@unh.edu;


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6/05/2017  |   10:00 - 10:15   |  306A

DECAY OF MACROALGAE AND LEAVES AND THEIR RELATION TO DETRITAL FOOD WEBS This project addressed if decaying macroalgae and leaves played a major role in the detrital pool of a 7th-order karst river. Decay rates and changes in carbon and nitrogen isotopic ratios of Cladophora glomerata, Platanus occidentalis, and a mix of Acer negundo and A. saccharinum were tracked during summer and autumn–spring. Packs of air-dried C. glomerata, P. occidentalis, and Acer were placed in mesh bags and put in groups (n=4) in wire baskets. Seven baskets were submerged in riffle (20–30 cm) and run (2 m) habitats. Isotopic values of Cladophora were not significantly different than leaves in summer but were significantly more δ¹³C-depleted in autumn–spring. Cladophora had significantly lower macroinvertebrate richness and shredder abundance in both summer and autumn–spring. Seasonality had a strong influence on decay rates, leading to greater mass loss of all three species in the summer compared to autumn–spring. Low richness and low shredder abundance on decaying macroalgae suggests Cladophora is not consumed by macroinvertebrates but used strictly as habitat, passing only through a microbial food web before being mineralized as CO₂.

Megan Grandinetti (Primary Presenter/Author), Western Kentucky University , Megan.grandinetti799@topper.wku.edu;


Scott Grubbs ( Co-Presenter/Co-Author), Western Kentucky University, scott.grubbs@wku.edu;


Albert Meier ( Co-Presenter/Co-Author), Western Kentucky University, albert.meier@wku.edu;


Delaney Rockrohr ( Co-Presenter/Co-Author), Western Kentucky University, delaney.rockrohr214@topper.wku.edu;


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6/05/2017  |   10:15 - 10:30   |  306A

EVALUATING SPATIAL AND TEMPORAL VARIATION OF ORGANIC-MATTER DECOMPOSITION TO ASSESS STREAM ‘HEALTH’ Organic-matter decomposition has been proposed as an integrative measure to detect human impacts to streams and rivers. However, fundamental information is lacking about spatial and temporal variation in decomposition rates among reference streams, which can limit the sensitivity of decomposition assays. In response, we evaluated among-stream and interannual variation in organic-matter decomposition in 26 reference streams in Michigan’s Upper Peninsula (USA) for 7 consecutive years (~182 stream-years) using the cotton-strip assay. Significant variation in decomposition rates (as percent tensile-strength loss of standardized cotton fabric) was observed among streams and among years. These spatial and temporal factors explained a similar and considerable amount of variation on a per-stream and per-year basis. Contrary to expectations, analyses of temperature-corrected decomposition rates did not reduce a large amount of variation among streams or years. Best subsets regression with environmental data from each stream, from a single year, indicated that variability in nutrient concentrations among streams, especially phosphorus and nitrogen, may contribute to variation in decomposition rates. By quantifying and assessing background variation, we hope to help develop a sensitive, reliable, and easy-to-use tool for assessing human impacts to stream ecosystems.

Emily Messick (Primary Presenter/Author), Dept. of Biological Sciences, Oakland University, elmessic@oakland.edu;


Mark Isken ( Co-Presenter/Co-Author), Dept. of Decision and Information Sciences, School of Business Administration, Oakland University, isken@oakland.edu;


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


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