Algal pigments in sediments as a measure of eutrophication in the Baltic environment

Abstract

A method of quantitative comparison of eutrophication of an area is proposed for the Baltic Sea, based on pigment content in sediments. The pigments concerned were chlorins a (i.e. chlorophylls a, b and selected chlorophyll a derivatives) and chlorophylls c. The analyses were performed on 300 samples from different layers of recent (0–10 cm) sediments, collected from about 50 stations, at different sites of the southern Baltic, including the estuaries of the two largest Polish rivers, in different seasons between 1992 and 2001, before and after the great flood of July 1997. The results are related to sampling site, sediment layer and hydrological conditions and also to organic carbon and E h in sediments, oxygen and salinity in near-bottom waters. Depending on different chlorin a content in 0–1 and 0–10 cm layers, the sampling sites are classified into one of three groups: 1. Szczecin Lagoon and the Deep of Gdańsk stations (permanently eutrophic, chl a in 0–1 cm >40 nmol/g, Σchlns a in 0–1 ⩾in 0–10 cm layer, Σchlns a A in Σchlns a=55–65%), 2. Open sea stations (mesotrophic/oligotrophic, chl a in 0–1 cm <10 nmol/g, Σchlns a in 0–1 ≫ in 0–10 cm layer, Σchlns a A in Σchlns a ∼50%; and 3. Coastal stations (periodically eutrophic, chl a in 0–1 cm 10–40 nmol/g, Σchlns a A in Σchlns a ∼40%). The correlation coefficient between chlorophyll a and chlorophylls b and c indicates the classes of algae, which could be the main source of organic matter in the sediments. A high correlation with chlorophylls c is a marker of diatoms; a high correlation with chlorophyll b is a marker of green algae; and low correlation both with chlorophylls b and c—indicates a high blue–green algae input.