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

Phytoplankton and bacteria are sensitive indicators of environmental  change. The temporal development of these key organisms was  monitored from 1988 to the end of 2007 at the time series station  Boknis Eck in the Western Baltic Sea. This period was characterized  by the adaption of the Baltic Sea ecosystem to changes in the  environmental conditions caused by the collapse and conversion of  the political system in the Southern and Eastern Border States,  accompanied by the general effects of global climate  change. Measured variables were chlorophyll, primary production,  bacteria number, -biomass and -production, glucose turnover rate,  macro-nutrients, pH, temperature and salinity. Negative trends with  time were recorded for chlorophyll, the bacterial variables, nitrate, ammonia, phosphate, silicate, oxygen and  salinity while temperature, pH, and the ratio between bacteria  numbers and chlorophyll increased. The strongest reductions with  time occurred for the annual maximum values, e.g. for chlorophyll  during the spring bloom or for nitrate during winter, while the  annual minimum values remained more stable. In deep water above sediment  the negative trends of oxygen, nitrate, phosphate and bacterial  variables as well as the positive trend of temperature were similar  to those in the surface while the trends of salinity, ammonia and  silicate were opposite to those in the surface. Decreasing oxygen  even in the surface layer was of particular interest because it  suggested enhanced recycling of nutrients from the deep hypoxic  zones to the surface by vertical mixing. In the long run all  variables correlated positively with temperature, except chlorophyll  and salinity. Salinity correlated negatively with all bacterial  variables as well as precipitation and positively with  chlorophyll. Surprisingly, bacterial variables did not correlate  with chlorophyll which may be inherent with the time lag between the  peaks of phytoplankton and bacteria during spring. Compared to the  20-yr averages of the environmental and microbial variables, the  strongest negative deviations of corresponding annual averages were  measured about ten years after political change for nitrate and bacterial secondary  production (~ −60%),  followed by chlorophyll (−50%) and bacterial  biomass (−40%). Considering the circulation of surface  currents in the Baltic Sea we conclude that the improved management  of water resources after 1989 together with the  trends of the climate variables salinity and temperature were  responsible for the observed patterns of the microbial variables at  the Boknis Eck time series station.

Hoppe H.-G., Giesenhagen H. C., Koppe R., Hansen H.-P. & Gocke K., 2012. 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. Biogeosciences Discussions 9: 18655-18706. Article.

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