MEPS 152:27-39 (1997)  -  doi:10.3354/meps152027

Measurements of microbial biomass and activity were carried out at 6 representative locations along a gradient of eutrophication in the Nordrügensche Bodden (southern Baltic Sea, Germany). Measurements in the water column revealed that turbidity, seston content, and concentrations of chlorophyll a and inorganic nutrients (ammonia, nitrite, nitrate, phosphate) increased from the outer to the inner parts of the Bodden whereas salinity decreased. Investigations of sediments confirmed this gradient of eutrophication. Whereas in the outer parts of the Bodden sandy sediments prevailed, sandy mud and muddy sediments dominated towards the inner parts. Generally, organic carbon and nitrogen, concentrations of chlorophyll a and phospholipids (indicator of microbial biomass), oxygen consumption and hydrolytic enzyme activities increased with increasing level of eutrophication. At the relatively unpolluted location in the outer parts of the Bodden, proteolytic enzymes dominated at the sediment surface. In subsurface horizons carbohydrate-decomposing enzymes gained more importance. At the heavily polluted locations in the inner parts of the Bodden, proteolytic enzymes were even more important. With increasing sediment depth enzyme activities were greatly reduced, however, and shifts in the spectrum of hydrolytic enzymes were less pronounced. Among the biological and chemical parameters, characteristic patterns of interrelationships became obvious, which led to the conclusion that microbial biomass and enzyme activities in sediments of the outer and central parts of the Bodden are limited by organic carbon. The organic-rich sediments of the inner parts of the Bodden, however, did not support further increases in microbial biomass and decomposition activities. Enzyme activities are discussed in relation to the composition and degradability of substrates. The enzymatic decomposition potential was measured by means of fluorogenic model substrates. Methodological investigations showed that the methylumbelliferyl substrates used reacted specifically enough to justify their use in ecological studies. Sediments can be stored refrigerated for over 2 mo without changes in the spectrum of hydrolytic enzymes.

Nordrügensche Bodden (Southern Baltic Sea) · Sediment · Eutrophication · Microbial biomass · Microbial activities · Enzymatic activities · Storage of sediments