Periphyton-water quality relationships along a nutrient gradient in the northern Florida Everglades

We monitored a 14-km nutrient gradient in the northern Everglades to identify statistical relationships between periphyton and water-quality changes caused by canal discharges into the marsh. Water chemistry measurements were taken at 15 sampling stations every 2 wk over a 20-mo period to quantify changes in major ions along the gradient. Standard algal bioassays were conducted using water from each station to identify trends in nutrient limitation and algal growth potential along the gradient. Patterns of periphyton biomass accumulation and taxonomic composition on artificial substrata were determined in situ during 6 sampling events across seasons. Concentrations of most ions decreased by <25% along the gradient, whereas average total phosphorus (TP) decreased from 150 mu g/L at peripheral marsh stations (near canal inflows) to less than or equal to 10 mu g/L at interior stations (>8 km from inflows). Limiting nutrient assays showed a shift from P limitation at interior stations to possible limitation by other nutrients at peripheral stations. Both algal growth potential and biomass accumulation decreased with increasing distance from the canal, and stepwise regression analysis showed that these changes were best explained by changes in TP along the water-quality gradient. Changes in periphyton taxonomic composition, analyzed using principal components analysis, were also related strongly to distance from canal discharges and to m. In particular, diatom species indicative of low TP (e.g., Anomoeoneis vitrea, Mastogloia smithii) were consistently replaced by eutrophic indicator species (e.g., Gomphonema parvulum, Nitzschia amphibia) at TP concentrations between 10 and 20 mu g/L. The Everglades periphyton assemblage is sensitive to phosphorus enrichment and may provide one of the first reliable indications of eutrophication in the marsh.