Nutrient Limitations for Harmful Algal Blooms in Urban Water Bodies in Queens, NY

Cyanobacterial harmful algal blooms (cHABs) are a global threat to drinking water supplies, sustainability of freshwater systems, and human health, due to cyanotoxin production. Recent upsurges in nutrient inputs have worsened the severity of cHABs, while proper nutrient management strategies to mitigate these blooms are still debated. My project focused on three lakes in Queens, NY that have experienced persistent cHABs (Bowne Pond, Kissena Lake, Goose Pond). I assessed phytoplankton species composition, algal biomass, and nutrient status in each system. I conducted experiments to determine the nutrient limitations of cHABs in the latter two water bodies by conducting nutrient dilution bioassays at two dilution levels (undiluted and diluted 1:3) and to test the individual and combined effects of N and P as triggers for nuisance growth of cyanobacteria. I measured algal biomass growth, changes in particulate and dissolved nutrients, and phytoplankton taxonomic composition in response to nutrient enrichment. Chlorophyll-a data indicated that Kissena Lake and Goose Pond were both hypereutrophic, with low algal species diversity dominated by cyanobacteria, and high particulate C, N, P, and N:P ratios, indicating P deficiency. Bowne Pond was eutrophic, with greater species diversity composed of several chlorophyte species, and it had lower particulate C, N, P, and C:P and N:P ratios, indicating N deficiency. Algal growth responses in the bioassays indicated that both in Kissena Lake and Goose Pond were P-limited in undiluted (“full-bloom”) conditions and co-limited by N and P in diluted conditions. Phytoplankton assemblages in the Kissena Lake experiment consisted mainly of N2-fixing and non-N-fixing cyanobacteria, while the Goose Pond experiment assemblages were dominated by non-N2-fixing cyanobacteria. The current NYS DEC nutrient management plan currently targets P input reduction to control cHABs in lakes, with less attention to managing N inputs. My findings suggest that more NYS lakes may be co-limited by N and P than previously understood, and N and P co-management is important in mitigating excess phytoplankton and cHAB growth