Nutrient Dynamics and Primary Productivity in a Biomanipulated Eutrophic Lake (2012)

Undergraduate: Shampa Panda

Faculty Advisor: John Wehr
Department: Health Environmental Sciences & Engineering

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This study was conducted on North Lake, located in a suburban community in Armonk, NY. It has been monitored seasonally for the past ten years for water clarity, chemistry, algal biomass, and phytoplankton community structure. North Lake receives nutrients from runoff over impervious surfaces, nuisance wildlife, and human activity. The lake shows evidence of eutrophication in the form of dense aquatic vegetation and high algal (phytoplankton) biomass. To determine the factors driving primary productivity and causing algal blooms, a mesocosm experiment was carried out. A 2 x 2 factorial design using nitrogen and phosphorus additions (control, nitrogen, phosphorus, nitrogen + phosphorus) was employed in 12, 4-L cubitainers. Each mesocosm was tested for water chemistry (NH4+, NO3-, total dissolved nitrogen, PO43-, and total dissolved phosphorus), chlorophyll a, and phytoplankton composition at time zero, three hours, and 4 days. Chlorophyll-a data for each experiment was averaged for all three replicates. In all three experiments the +NP treatment resulted in greatest algal biomass. Nitrogen uptake was measured against algal biomass, with highest amounts of uptake in the +P treatments. Phosphorus uptake was also measured against algal biomass, with highest amounts of uptake in the +P treatment. These data indicate that algal biomass (chlorophyll-a) was co-limited by nitrogen and phosphorus, and that nutrient uptake (both N and P) was limited by phosphorus availability.