The use of nutrient enrichment bioassays to test for limiting factors affecting epiphytic growth in Lake Okeechobee, Florida: confirmation of nitrogen and silica limitation

Nutrient enrichment bioassays were developed to test for nitrogen (N), phosphorus (P), and silica (Si) limitation of epiphytic biomass in eutrophic Lake Okeechobee, Florida, USA. Quarterly assays on artificial (plastic) Hydrilla plants exposed to lake water for 7 days prior to nutrient addition were evaluated by changes in chlorophyll-a relative to controls. Epiphytic biomass was measured at 24-h intervals for 72 h; nitrogen and silica additions had a stimulatory effect on biomass during all experiments, whereas phosphorus additions were never stimulatory. These results are consistent with recent analyses of phytoplankton growth limitation by nitrogen in this phosphorus-enriched ecosystem, and additionally suggest silica should be considered as a limiting nutrient for microalgal communities dominated by diatoms.