Free and particle-associated extracellular enzyme activity and bacterial production in the lower Elbe estuary, Germany

A high abundance of particles and aggregates is a characteristic of estuaries and may represent important loci of increased bioproductivity and microbial activity. From a survey performed in the Elbe estuary, particle concentration (using a particle counter), bacterial biomass and abundance (AODC method), bacterial production rates ([H-3] thymidine method) and the microbial extracellular enzyme activity of 11 enzymes (MUF and MCA method) were determined with particular respect to their relationship to particles and aggregates (size-fractionated). Although higher particle abundance was found compared to other sections of the river Elbe, neither relative nor absolute bacterial activity associated with particles and aggregates was enhanced. The activity of free dissolved microbial enzymes was found to dominate the breakdown of organic material. The productivity of free dispersed bacteria greater than or equal to0.2...<2 mu m (2...69%) and bacteria attached to small particles >= 2...<10 mum (27...93%) considerably surpassed that of bacteria associated with particles >10 mum (0...40%). This indicates that the larger particles and aggregates do not always contribute substantially to the overall microbial activity in rivers and estuaries.