The role of microbial processes in the phosphorus flux regulation between sediments and water

Abstract

Lake internal phosphorus-recycling from sediments is a significant process in most eutrophic shallow lakes.The mechanisms for P-liberation in the sediments are coupled microbial processes depending on water transport at the sediment-water interface. Thereby electron acceptors are supplied to sessile microassemblages of bacteria and inhibitory products, such as hydrogen sulphid, are removed by water transport. This relations where shown by timeseries in interstitial water strata and lake-budget calculations for several lakes in the Berlin-region, the Schlei-estuary and Swedish lakes.In shallow eutrophic lakes up to 1 g/m 2 /month phosphorus have been liberated by the process of internal fertilisation from sediments during short periods in summer and autumn. This was equal to the whole phosphorus content of the upper 2 mm of surface sediments and resulted in a large increase of phosphate concentration in water column. The periods of internal P-liberation where coupled with high rates of plankton sedimentation and depleted oxidized nitrogen by denitrification in sediment surface. In these periods desulfurication became the main respiration-process in sediment metabolism.The sediment studies showed a monocausal hierachy of processes. The energyflow partly resulting in water transport and in chemical reactions control the sediment metabolism with respect to space and time distribution of microbial activity.In aquatic sediments the mineralization of organic matter regenerates phosphates, resulting in an accumulation of phosphates in the interstitial water and the formation of a concentration gradient. The subsequent diffusive transport to the overlying water is affected by chemical and microbial processes. Especially the redox state of the sediment is known to be an important factor determining the actual phosphate flux. The presence of an oxidized microlayer at the sediment surface is considered to be an important trap for phosphates. The high adsorption capacity of the oxidized microzone is generally ascribed to the presence of iron(III)-hydroxides. Lately, also the role of microorganisms has come into focus. Microorganisms in the surface layer of the sediment might act as a redox dependent source/sink mechanism of phosphates.This contribution is focused on the role of methane oxidizing bacteria in the sediment surface. In Lake Loosdrecht almost the entire methane flux diffusing upward is oxidized in the sediment surface layer. In periods with high methane production the major fraction of the oxygen consumption of the sediment can be ascribed to methanotrophic bacteria. An experimental setup will be described which enabled us to manipulate the methane flux toward the sediment surface. Microelectrode equipment was used to quantify the oxygen consumption and the oxygen penetration depth. In columns with high activity of methanotrophic bacteria a decrease in the oxygen penetration depth could be demonstrated. However, these columns appeared to have a higher phosphate adsorption capacity than the controls. Batch experime...

Distribuição espaço-temporal e balanço de massa do fósforo na represa de Salto Grande-Americana (SP)

“…Muitos trabalhos têm demostrado a importância do sedimento na liberação ou na imobilização de fósforo da água. Diferentes fatores têm sido sugeridos como causas de influência nas taxas de liberação de fósforo do sedimento para água, tais como: condições redox, pH, temperatura da água, grau de mineralização, concentração de nitrato, presença de macrófitas e perifiton, difusão e turbulência provocadas por ventos e diferentes características do sedimento (MATLNVESI & HEINONEN-TANSKI, 1992;GOLTERMAN et al, 1993;RIPL, 1993;SARAZCsf et al, 1993;SINKE et al, 1993;PHILLIPS et al, 1994). Tanto os processos abióticos como os bióticos causam liberação de fósforo do sedimento.…”