Author: Rebecca L North,  Assistant Professor (University of Missouri)

Description:
In the agricultural Midwest (USA), ubiquitous reservoirs experience eutrophy and hypolimnetic anoxia. Here, we explore influences of eutrophication and land-use on the proximate light and nutrient status of phytoplankton communities in 32 Missouri reservoirs. Light and nutrient status indicators include mixed layer irradiance, phosphorus (P) and nitrogen (N) stoichiometry/debts, photosynthetic efficiency, and photosynthetic-irradiance parameters. We evaluate if phytoplankton biomass and productivity are constrained by light, P, N, or a combination thereof, across gradients of trophic status and land-use during 2 contrasting wet and dry summers. Despite agricultural prevalence, P-deficiency is more prominent than either N- or light-deficiency. Gross primary productivity per unit chlorophyll-a (GPP^B) demonstrates negative relationships with nutrients, biomass, and turbidity, and positive relationships with light availability. GPP^B is highest in oligotrophic reservoirs where light utilization efficiency is also highest. Overall, phytoplankton biomass and productivity appear constrained by P and light, respectively. If Midwestern reservoirs are precursors of future inland waters affected by climate change and eutrophication, our crystal ball indicates that both P and light will be important regulators of phytoplankton dynamics and subsequent water quality.

Category: Scientific Program Abstract > Special Session > SS68 Understanding reservoir function in a changing world