SHADING OF PERIPHYTON COMMUNITIES BY WETLAND EMERGENT MACROPHYTES - DECOUPLING OF ALGAL PHOTOSYNTHESIS FROM MICROBIAL NUTRIENT RETENTION

Relative net primary productivity (NPP) of periphyton communities in t he Florida Everglades were determined and compared under emergent macr ophyte canopies typical of enriched and unenriched Everglades habitats . Photosynthetically active radiation (PAR) reaching the periphyton co mmunities were reduced only by 35% in sawgrass (Cladium mariscus) habi tats but by 85% or more in dense stands of cattail (Typha domingensis) . Photosynthetic rates of periphytic algae and cyanobacteria in sawgra ss habitats were about 70% of those in open water slough habitats. NPP of periphytic communities within the cattail habitat was severely red uced by 80 +/- 8 per cent of rates in the open communities. Greatly re duced inorganic and organic P concentrations occurred in water of habi tats with high periphytic photosynthesis, whereas inorganic and organi c nitrogen concentrations were lower in the nutrient-enriched, more re ducing cattail habitats. Putative causes for these observations are re lated to the suppression of periphytic photosynthesis by macrophytic s hading.