Rapport nr 98: Hydrografi, primärproduktion, växtplanktonsammansättning, bottenfauna, kräft- och fiskbestånd i Vargsundet sommaren 1998
NUMMELIN, C; PERUS, J (1999)
NUMMELIN, C
PERUS, J
Åbo Akademi, Husö biologiska station
1999
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Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:952-12-0360-9
https://urn.fi/URN:ISBN:952-12-0360-9
Tiivistelmä
Summer 1998, hydrography, primary production, phytoplankton composition, zoobenthos, standing crop of crayfish and fish were studied in the lake Vargsundet (Ösundet) on the central Åland Islands. Summer 1997, dense blooms of the ichtyotoxic haptophyte Prymnesium parvum killed large amount of fish in the lake.
The lake Vargsundet is a deep (31 m) meromictic lake with higher salinity in the deeper layers than in the surface layers. Anoxic conditions were recorded below 9 meters in early August. Nutrient concentrations were considerably higher in the deeper anoxic layers than in the oxic layers. Primary production peaked in the northern basin in July with values around 25 mgC/m3h and in the southern basin in the end of June with values around 87 mgC/m3h. Dominant phytoplankton groups were cyanophytes, cryptophytes, chrysophytes and diatomophytes. Dominant zoobenthos taxa were Chironomus spp., Ostracoda, Copepoda and Pterozygota. The biomass of the standing stock of fish in the lake was dominated by roach (Rutilus rutilus) and perch (Perca fluviatilis).
The lake shows clear signs of eutrophication, such as high primary production and elevated nutrient concentrations. In addition, many phytoplankton, zoobenthos, and fish species are characteristic for eutrophicated water systems.
No toxic plankton blooms were recorded in 1998. Neither could any direct effects of the blooms in 1997 be shown on any of the physico-chemical or biological parameters studied.
The lake Vargsundet is a deep (31 m) meromictic lake with higher salinity in the deeper layers than in the surface layers. Anoxic conditions were recorded below 9 meters in early August. Nutrient concentrations were considerably higher in the deeper anoxic layers than in the oxic layers. Primary production peaked in the northern basin in July with values around 25 mgC/m3h and in the southern basin in the end of June with values around 87 mgC/m3h. Dominant phytoplankton groups were cyanophytes, cryptophytes, chrysophytes and diatomophytes. Dominant zoobenthos taxa were Chironomus spp., Ostracoda, Copepoda and Pterozygota. The biomass of the standing stock of fish in the lake was dominated by roach (Rutilus rutilus) and perch (Perca fluviatilis).
The lake shows clear signs of eutrophication, such as high primary production and elevated nutrient concentrations. In addition, many phytoplankton, zoobenthos, and fish species are characteristic for eutrophicated water systems.
No toxic plankton blooms were recorded in 1998. Neither could any direct effects of the blooms in 1997 be shown on any of the physico-chemical or biological parameters studied.