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 the Florida Everglades were determined and compared under emergent macrophyte canopies typical of enriched and unenriched Everglades habitats. Photosynthetically active radiation (PAR) reaching the periphyton communities were reduced only by 35 % in sawgrass (Cladium mariscus) habitats but by 85 % or more in dense stands of cattail (Typha domingensis). Photosynthetic rates of periphytic algae and cyanobacteria in sawgrass habitats were about 70 % of those in open water slough habitats. NPP of periphytic communities within the cattail habitat was severely reduced by 80 ± 8 per cent of rates in the open communities. Greatly reduced inorganic and organic P concentrations occurred in water of habitats with high periphytic photosynthesis, whereas inorganic and organic nitrogen concentrations were lower in the nutrient-enriched, more reducing cattail habitats. Putative causes for these observations are related to the suppression of periphytic photosynthesis by macrophytic shading.