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Muddy Bottom Macrofauna Of The Szczecin Lagoon Over The Period 
Which Followed The Peak Of The Flood 
Norbert Wolnomiejski & Irena Grygiel 
Sea Fisheries Institute 
Branch of Swinoujscie 
Plac Slowinski 11 
72-600 Swinoujscie 
Abstract 
Macrobenthos was used as a bioindicator of the state of the Szczecin Lagoon environmental 
conditions during and after the '97 flood event. There was a potential threat of an excessive 
increase of various pollutant concentrations transported with the riverine waters. The Lagoon 
is the main transition (estuarine) zone between the Odra river and the Pomeranian Bay. 
The conduced studies were focused on the largest habitat of the Lagoon bottom i.e. the muddy 
bottom covering 225 km 2 and constituting 55 % of the total Polish area of the Lagoon. The 
data obtained over the period 6 August - 7 October 1997 were referred to the results gathered 
at the same sampling sites and the same months of the years 1987-1996. 
Chironomus plumosus larvae and Oligocheta (with predomination of Potamothrix hammoni- 
ensis) constituting on average 74 % and 25 % of a total biomass, respectively, were the main 
macrofauna components. A distinct, negative influence of the flood was visible only in the area 
of Roztoka Odrzanska (southern region of the Lagoon), constituting less than 6 % of the entire 
area of the investigated reservoir, and being the first recipient of the Odra waters. That region 
was characterized by muddy macrofauna scarcity, its average biomass being equal 9.3 g/m 2 . 
Macrofauna biomass of Roztoka Odrzanska, in particular the Chironomus plumosus biomass, 
was lower than the long-term minimum values, which most probably resulted from worsening 
of feeding conditions due to an increased sedimentation of large fractions of suspended matter, 
in particular the mineral ones, and due to limited phytoplankton development resulting from a 
great rate of water flow during the flood. The wide, central part of the Lagoon did not exhibit 
any effects of the flood, either negative (i.e. lethal influence of toxic substances) or positive 
ones. The macrofauna biomass there was abundant (on average 70 g/m 2 ), thus higher than the 
long-term mean value but falling into the long-term range. 
High homeostatic capacity of the Szczecin Lagoon ecosystem counterbalanced to a great ex 
tent the negative impact of the 1997 flood on the muddy bottom macrofauna communities. The 
high benthos biomass observed in the major part of the Szczecin Lagoon, particularly seen 
over the period of the last five years, remained at the same level in 1997.