Impact of change in climate and policy from 1988 to 2007 on environmental and microbial variables at the time series station Boknis Eck, Baltic Sea

[摘要] Phytoplankton and bacteria are sensitive indicators of environmentalchange. The temporal development of these key organisms wasmonitored from 1988 to the end of 2007 at the time series stationBoknis Eck in the western Baltic Sea. This period was characterizedby the adaption of the Baltic Sea ecosystem to changes in theenvironmental conditions caused by the conversion ofthe political system in the southern and eastern border states,accompanied by the general effects of global climatechange. Measured variables were chlorophyll, primary production,bacteria number, -biomass and -production, glucose turnover rate,macro-nutrients, pH, temperature and salinity. Negative trends withtime were recorded for chlorophyll, bacteria number, bacterialbiomass and bacterial production, nitrate, ammonia, phosphate, silicate, oxygen andsalinity while temperature, pH, and the ratio between bacterianumbers and chlorophyll increased. Strongest reductions withtime occurred for the annual maximum values, e.g. for chlorophyllduring the spring bloom or for nitrate during winter, while theannual minimum values remained more stable. In deep water above sedimentthe negative trends of oxygen, nitrate, phosphate and bacterialvariables as well as the positive trend of temperature were similarto those in the surface while the trends of salinity, ammonia andsilicate were opposite to those in the surface. Decreasing oxygen,even in the surface layer, was of particular interest because itsuggested enhanced recycling of nutrients from the deep hypoxiczones to the surface by vertical mixing. The long-term seasonalpatterns of all variables correlated positively with temperature, except chlorophylland salinity. Salinity correlated negatively with all bacterialvariables (as well as precipitation) and positively withchlorophyll. Surprisingly, bacterial variables did not correlatewith chlorophyll, which may be inherent with the time lag between thepeaks of phytoplankton and bacteria during spring. Compared to the20-yr averages of the environmental and microbial variables, thestrongest negative deviations of corresponding annual averages weremeasured about ten years after political change for nitrate and bacterialsecondary production (~ −60%),followed by chlorophyll (−50%) and bacterialbiomass (−40%). Considering the circulation of surfacecurrents in the Baltic Sea we interpret the observed patterns of the microbial variables atthe Boknis Eck time series station as a consequence of the improved managementof water resources after 1989 and – to a minor extent – thetrends of the climate variables salinity and temperature.

[学科分类] 地球化学与岩石