RESILIENCE OF PELAGIC AND BENTHIC MICROBIAL COMMUNITIES TO SEDIMENT RESUSPENSION IN A COASTAL ECOSYSTEM, KNEBEL-VIG, DENMARK

The effects of resuspension on benthic and pelagic photosynthesis, bac terial production, denitrification and other aspects of C- and N-cycli ng were studied in a Danish coastal water system. Experiments were don e in two 3.6-3.8 m deep mesocosms where resuspension was generated by stirring of the water. Six millimetres of the sediment was suspended, causing a reduction of Secci-depth in the overlying water to 10 cm. Th e system studied was N-limited and had considerable populations of ben thic diatoms and cyanobacteria with photosynthetic activity of the sam e magnitude or larger than the pelagic. The algae created a distinct m at on the sediment surface and effectively controlled the sediment-wat er fluxes of dissolved inorganic nitrogen. During resuspension, the O- 2 content of the water in the two mesocosms decreased by 5%, and chlor ophyll a content in the water increased by 28%, corresponding to a tra nsport of only 2% of the benthic algal chlorophyll to the water phase. Primary production and nutrients in the pelagic were not affected, bu r bacterial production increased for 1 day. After resuspension, the av erage benthic chlorophyll was unchanged, but was more unevenly distrib uted. Benthic primary production was affected for 1 week after the eve nt, mostly due to water turbidity; dark respiration and fluxes of N-sp ecies were unchanged. Denitrification rates were stimulated in resuspe nded mesocosms relative to undisturbed controls. The system studied sh owed remarkable stability with some short-term responses to resuspensi on and almost all measured parameters returned to status quo within 1 week. (C) 1996 Academic Press Limited