Periphyton responses to nitrogen and phosphorus enrichment of shallow lake systems dominated by submerged plants: A mesocosm study

Abstract

The responses of periphyton to enrichment with nitrogen and phosphorus have been investigated in shallow lakes with low macrophyte biomass, but less is known about shallow lakes dominated by submerged plants. We examined the biomass and species composition of periphyton in 12 mesocosms dominated by Vallisneria natans (Lour.) Hara and subjected to different nitrogen and phosphorus enrichment regimes. Periphyton biomass measured as Chlorophyll a (Chl a) was higher in the nitrogen-enriched treatment relative to the controls. Chl a initially increased with phosphorus and nitrogen + phosphorus enrichment, but declined towards the end of the experiment. This delayed negative response of periphyton to nutrient enrichment appeared to be due to increased phytoplankton concentrations which inhibit light availability (nitrogen + phosphorus additions) and to increased growth of V. natans (phosphorus additions). Shifts in species composition of periphyton also occurred with different treatments. Our work demonstrated that periphyton are significantly affected by enrichment with nitrogen and phosphorus, and helped clarify the ecological role of these important primary producers.