SFS Annual Meeting

5/21/2018  |   11:00 - 11:15   |  321

SEASONAL PATTERNS IN ALGAL BIOMASS ALTER THE STOICHIOMETRY OF EXTRACELLULAR ENZYME MEDIATED NUTRIENT CYCLING IN AN AGRICULTURALLY INFLUENCED OXBOW LAKE Four years of water column nutrient, sediment, chlorophyll a (chl. a) and extracellular enzyme activity (EEA) data from an oxbow lake were examined to quantify stoichiometric responses of EEA to seasonal patterns in algal biomass. Chl. a was limited by sediment concentrations exceeding 120 mg/L, primarily in winter and spring. Scaling relationships between beta-glucosidase (BG), beta-N-acetylglucosaminindase (NAG) + l-leucine aminopeptidase (LAP) and acid phosphatase (AP) activity were all significant. Scaling relationship slopes were significantly greater for BG vs NAG+LAP and BG vs AP activities indicating that metabolism of organic C was upregulated more than N or P when chl. a exceeded 65 µg/L . Slopes for NAG+LAP vs AP activity were not different for chl. a categories representing < 100 µg/L. Yet, when chl. a exceeded 100 µg/L the slope was significantly lower, indicating an increasing reliance on organic P metabolism to meet nutrient demands during period of high productivity. Results demonstrate that seasonal patterns in light limitation and algal biomass contribute to stoichiometric patterns of EEA expression and suggest that these nutrient cycling pathways are influenced by autotroph-heterotroph interactions within eutrophic oxbow lakes.

Jason M. Taylor (Primary Presenter/Author), USDA, Agricultural Research Service, National Sedimentation Lab, jason.taylor@ars.usda.gov;


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5/21/2018  |   11:15 - 11:30   |  321

LEAF LITTER DECOMPOSITION IN EUTROPHIC PONDS Nutrient enrichment and pond construction are prevalent watersheds alterations. Nutrient enrichment stimulates primary production in both streams and ponds, resulting in eutrophication. In streams, nutrient enrichment can accelerate litter decomposition, suggesting direct nutrient limitation of heterotrophs. However less is known about the interaction of nutrient enrichment and heterotrophy in ponds. Our research shows that ponds in central Virginia are both eutrophic and have high terrestrial leaf litter standing stocks (mean = 189.5 g AFDM m^-2). In these ponds, litter decomposition is slow (mean k = 0.0030 d^-1) and is likely inhibited by the effects of eutrophy (e.g., hypoxia, reduced animal diversity, etc...). Using microcosm experiments, we show that nutrient enrichment does not directly stimulate leaf litter decomposition in these ponds. However, other experiments show greater leaf decomposition when leaf litter is in contact with sediments from eutrophic ponds. These results suggest that the impact of eutrophication on litter decomposition in ponds may be indirect and complex.

Kenneth Fortino (Primary Presenter/Author), Longwood University, fortinok@longwood.edu;


Kaitlyn Peters (Co-Presenter/Co-Author), Longwood University, kaitlyn.peters@live.longwood.edu;


Julia Marcellus (Co-Presenter/Co-Author), Longwood University, julia.marcellus@live.longwood.edu;


Jennifer Andrews (Co-Presenter/Co-Author), Longwood University, jennifer.andrews@live.longwood.edu;


Leanna Tacik (Co-Presenter/Co-Author), Longwood University, leanna.tacik@live.longwood.edu;


Jessica Hoak (Co-Presenter/Co-Author), Virginia Tech, jessica.hoak@live.longwood.edu;


Matthew Waters (Co-Presenter/Co-Author), Auburn University, mwaters@auburn.edu;


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5/21/2018  |   11:30 - 11:45   |  321

BLURRED LINES: AUTOTROPHIC AND HETEROTROPHIC FOOD RESOURCES AND MACROINVERTEBRATE COMMUNITIES IN HEADWATER STREAMS Food webs of temperate, forested headwater streams are energetically supported by leaf debris decomposed by microbes and macroinvertebrate shredders. Recent studies suggest algae may influence leaf decomposition and shredder growth. Thus, leaf-associated algae may correspond to macroinvertebrate communities. We manipulated light in three high and three low nutrient streams in Maryland’s Piedmont in winter 2017. In each stream, five red maple leaf bags were exposed to ambient light and five were shaded; macroinvertebrates and algae were recovered from leaves after four weeks. Algal biomass (chlorophyll-a) was significantly higher under ambient light (p<0.001) and high nutrient conditions (p=0.001). Macroinvertebrate abundance exhibited a significant interaction (p=0.006; lowest abundance: ambient light/low nutrient). Total macroinvertebrate biomass and diversity (Hill numbers) did not vary. Predator and collector-filterer abundance was highest in high nutrient conditions (p=0.009, p=0.039, respectively), and collector-filterer abundance was highest in shade (p=0.002). Ephemerellid abundance increased with light (p<0.001), showed a significant interaction (p=0.007), and was significantly correlated to algal biomass (r=0.417, p=0.001). These results suggest specific macroinvertebrate taxa may shift relative to leaf-associated algae although community level responses may be limited. Stream restoration techniques may improve with the application of leaf-algae-macroinvertebrate relationships.

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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5/21/2018  |   11:45 - 12:00   |  321

EFFECTS OF LIGHT AND THE SELECTIVELY OMNIVOROUS SHRIMP MACROBRACHIUM OHIONE ON DETRITAL MICROBIAL BIOFILMS IN STREAMS In lotic freshwater systems, aquatic macroinvertebrates are key processors of biofilms that grow upon organic matter. Although the effects of macroinvertebrates on biofilms may depend on light availability, the combined effects of consumers and light remain unexplored. Here, we tested effects of presence versus absence of the shrimp Macrobrachium ohione on Liriodendron tulipifera biofilms in experimental streams under full light or darkness. We measured algal and fungal biomass and production rates, as well as litter decomposition, over 49 days. Light significantly increased algal production and exudation rates (P<0.001) while temporal effects in algal production and exudation depended on shrimp presence or absence (P<0.001). Fungal biomass was significantly greater under dark treatment (P<0.05) but did not respond to shrimp manipulation, and fungal production rates did not differ across treatments, but fungal growth rates were significantly stimulated in light (P<0.05). Litter decomposition rates did not depend on light or shrimp treatments. These results suggest that light can change multiple characteristics of litter biofilms and, while M. ohione may not affect the biofilm overall, this consumer species can have a measurable effect on the timing of periphytic algal colonization of organic matter.

Cheyenne Brady (Primary Presenter/Author), University of Southern Mississippi, w864850@usm.edu;


Halvor Halvorson (Co-Presenter/Co-Author), University of Central Arkansas, hhalvorson@uca.edu;


Kevin A. Kuehn (Co-Presenter/Co-Author), University of Southern Mississippi, kevin.kuehn@usm.edu;


Steve Francoeur (Co-Presenter/Co-Author), Biology Department, Eastern Michigan University, steve.francoeur@emich.edu;


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