Nitrogen versus phosphorus enrichment of brackish waters: responses of the submersed plant Potamogeton perfoliatus and its associated algal community

Abstract

Potamogeton perfoliatus was formerly an abundant component of brackish waters of Chesapeake Bay prior to a general decline in submersed plants associated with eutrophication. Additions of both N and P caused significant increases in biomass accumulation of epiphytic and phytoplanktonic communities. The effects of N and P on algal densities were synergistic in that responses to N addition were greatest at high P loading and vice versa. At the highest nutrient treatment rates, combined amendments (N plus P) resulted in significantly greater increases in epiphytes and phytoplankton than did the same high inputs of either nutrient (N or P) individually. Associated with increased algal densities at high nutrient loading rates, there were significant decreases in growth and biomass of P. perfoliatus. Significant inverse correlations were found between epiphyte density and plant growth and biomass as well as light attenuation. Management efforts to restore submersed plants such as P. perfoliatus by reducing eutrophication, and associated light attenuation by algae, should consider reducing inputs of both N and P. -from Authors