THE USE OF NUTRIENT ENRICHMENT BIOASSAYS TO TEST FOR LIMITING FACTORSAFFECTING EPIPHYTIC GROWTH IN LAKE-OKEECHOBEE, FLORIDA - CONFIRMATIONOF NITROGEN AND SILICA LIMITATION

Nutrient enrichment bioassays were developed to test for nitrogen (N), phosphorus (P), and silica (Si) limitation of epiphytic biomass in eu trophic Lake Okeechobee, Florida, USA. Quarterly assays on artificial (plastic) Hydrilla plants exposed to lake water for 7 days prior to nu trient 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 duri ng all experiments, whereas phosphorus additions were never stimulator y. These results are consistent with recent analyses of phytoplankton growth limitation by nitrogen in this phosphorus-enriched ecosystem, a nd additionally suggest silica should be considered as a limiting nutr ient for microalgal communities dominated by diatoms.