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5/23/2018  |   9:45 AM - 10:00 AM   |  BOTTOM-UP AND TOP-DOWN FACTORS INFLUENCING PERIPHYTON COMMUNITY STRUCTURE ACROSS A STREAM CURRENT VELOCITY GRADIENT   |  330 B

BOTTOM-UP AND TOP-DOWN FACTORS INFLUENCING PERIPHYTON COMMUNITY STRUCTURE ACROSS A STREAM CURRENT VELOCITY GRADIENT

Stream current velocity is a master variable that can modify bottom-up and top-down factors influencing periphyton production and community structure. Current velocity impacts nutrient uptake and invertebrate consumption rates, but field experiments have rarely examined these processes simultaneously. We used nutrient diffusing substrates to add nutrients and an electric fence to exclude invertebrates across a velocity gradient of 2-30 cm/second. We measured algal biomass (chlorophyll a), organic matter (ash-free dry mass), and several pigments representing algal community composition. ANOVAs showed that algal biomass responded to nutrient but not consumer treatments, with current velocity positively affecting algal responses to limiting nutrients. In contrast, organic matter decreased significantly with consumers but did not respond to nutrient additions. Finally, algal community composition responded to nutrient additions and current velocity but not consumer treatments. Nitrogen+Phosphorus treatments increased the proportion of cyanobacteria and decreased the proportion of green algae, while current velocity increased the proportion of green algae but decreased the proportion of diatoms. These experiments measured treatment effects on early successional periphyton communities (up to 16 days old), but future experiments will focus on more developed communities across a wider velocity range.

  • Limitation
  • Nutrients
  • Periphyton

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Presenters/Authors

Whitney Beck (), Environmental Protection Agency, Beck.Whitney@epa.gov;


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LeRoy Poff (), Colorado State University, n.poff@rams.colostate.edu;


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