Ecology of the Szczecin Lagoon diatom flora with reference to the utility of diatom indices in assessing water quality

Abstract

Abstract The study focuses on applying the diatom flora to evaluate environmental conditions of the Szczecin Lagoon. A total of 521 taxa (diatom species and varieties) of 74 genera were identified in the samples. Light microscope (LM) counts were processed with OM-NIDIA software to yield diatom indices. The diatom flora structure and relations between assemblages at individual sites were explored with multivariate analyses. Applicability of diatom indices in assessing the state of the Szczecin Lagoon was confirmed. The infer- ences produced by diatom indices were compared with those derivedfrom directly meas- uring physico-chemical water parameters and from using the diatom bioindicative charac-teristics. Diatom indices produced conclusions similar to those resulting from conventional application of diatom bioindicative potential. Both methods showed the Szczecin Lagoon to be eutrophic and moderately polluted. Key index words : Baltic Sea, bioindication, diatom indices, diatoms (Bacillariophyceae), Szczecin Lagoon Introduction Diatoms are commonly believed to be highly sensitive microorganisms, useful in environmental assessment. The presence or absence of certain taxa as well as their development allows to draw conclusions regarding the state of the water mi-lieu. The bioindicative potential of diatoms was explored in numerous studies in which salinity, eutrophication or saprobity was assessed (e.g. Geissler 1982, Geissler & Jahn 1984, Patrick 1984, Cox 1991, Fritz et al. 1991, Dixit et al. 1992, Round 1993, Hofmann 1994). A number of diatom-based environment assessment methods have been developed in recent decades. The methods involve matching certain diatom species of known indicative value to calculate the so-called diatom indices (Descy 1979, Lenoir & Coste 1996, SladeCek 1986, Prygiel et al. 1996, Dell'Uomo 1996, Kelly & Whitton 1995, Watan- abe 1986, Coste & Ayphassorho 1991). As the benthic diatom-based indices are now a major tool in riverine water quality assessment, it