Seasonal effect of zebra mussel colonies on benthic processes in the temperate mesotrophic Plateliai Lake, Lithuania

Abstract

Sparse colonies of zebra mussel (Dreissena polymorpha) create net heterotrophic sediment patches via respiration, excretion, and biodeposition activities, but their effect as biogeochemical hotspots is scarcely investigated in nutrient-limited ecosystems. We analyzed the seasonal effect of zebra mussel colonies on benthic respiration (O2, TCO2, N2, and CH4) and nutrient fluxes (NH4+, NOx−, SRP, and SiO2) in a macrophyte-dominated mesotrophic temperate lake. Intact sediments with and without zebra mussel aggregates were collected in winter, summer, and autumn, and incubated to measure fluxes. The contribution of mussel colonies alone to benthic metabolism was also quantified. Sediments with mussels always had higher rates of respiration (O2 and TCO2) and nutrient recycling (NH4+ and SRP) as compared to bare sediments, while there was no effect on CH4, NO3−, and SiO2 fluxes. Mussel colonies stimulated nitrogen removal via denitrification, but only in the summer. The effect of colonies was particularly evident in warmer periods, due to mussel respiration and excretion and to biodeposits that increased microbial activity in sediments. In this mesotrophic lake, mussel aggregates contribute to alleviate nutrient (N and P) limitation, but their heterotrophic activity is likely buffered by nutrient uptake and oxygen production by submersed vegetation.