Report: ‘Zooplankton: Wesermündung comparison 1983/84 and 1968»

The zooplankton community of the Weser estuary from Bremen to lighthouse “Roter Sand” was investigated in June 1983, June 1984 and August 1984. The qualitative and quantitative results are compared to those of a baseline study, which was carried out in 1967 and 1968 before a titanium dioxide factory started production and waste discharge into the Weser estuary in 1969. Number and spectrum of species seem to have remained almost constant compared to 1968. The Rotifer Synchaeta baltica, which is not recorded in 1968, come to mass development in the meso- and/or polihaline zone and cause the maximum located there in June. In the Weser River a fresh water zone with salinities below 0.3 Ω Cl does not exist any more due to pollution by brine from the potassium-industries upstream. The zooplankton density in the artificially salted area is extremely reduced. In all three months of investigation the zooplankton density in the natural brackish zone shows a similar distribution with two maxima, one in the meso- and/or polyhaline zone. Between them an estuarine Impoverishment zone is located. This pattern of distribution was found in 1968 by BODE and PUCK (1972), too, but compared to their results the actual investigations showed a marked increase of total zooplankton density as well as of the amplitude of density. It is not yet clear, whether this phenomenon could indicate disturbances caused by human influences. In view to the waste water discharge of the titanium dioxide factory a harmful influence could not be found. The zooplankton of the Weser estuary from the Red Sand lighthouse to Bremen was examined qualitatively and quantitatively in June 1983, June 1984 and August 1984. The results are compared with the baseline study in which the state was retained before the discharge of effluents from titanium dioxide production. As a result, it should be summarised: The zooplankton is clearly impoverished in the naturally limnic section between Bremen and Brake, which is now polluted by potash wastewater. In the actual brackish water, the species spectrum has essentially preserved itself. There are two zones of very dense plankton colonisation: one in low and one in higher salinity ranges. In both cases, densities have increased significantly compared to the 1968 baseline study. In medium salinity areas there is the natural impoverishment zone of brackish water, which in the past, as today, has only a weak settlement. Damage caused by wastewater is not detectable at the zooplankton of the order of magnitude investigated here.