Structure and function of bacterioplankton in the rehabilitated Lake Trzesiecko

Abstract

Changes in bacterioplankton in relation to the temperature and water chemistry in Lake Trzesiecko were studied from 2008 to 2013. The lake was highly eutrophic until 2005 when measures were begun to precipitate phosphate, to increase oxygen concentrations by re-aeration and to reduce algal crops through biomanipulation of the fish community. Some improvements were also made to reduce phosphorus levels in the inflows. Conductivity increased, redox potential remained largely unchanged, and pH decreased during the period. The abundance, biomass, and morphological structure of the bacterioplankton suggest Lake Trzesiecko remains eutrophic but bacterial numbers and biomass have declined since 2008. The decline was significantly related to decreases in concentration of nitrogen and phosphorus compounds. The bacterial community comprised mostly small cells (<0.05μm3), with a lower proportion of cells >0.1μm3. Most were cocci. A negative correlation between conductivity and bacterial numbers and biomass suggests that mineral salts from the phosphorus coagulant inhibited the bacterioplankton. Key nutrients (nitrogen and phosphorus) and DOC were positively related to bacterial biomass and numbers.