Chlorophyll - nutrients - Secchi disc relationships in the Great Mazurian Lakes (North-Eastern Poland)
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The relationships between SD, chlorophyll, total phosphorus and total nitrogen were analysed basing on data from 25 sites in 21 Great Mazurian Lakes collocted during 12 years. Best fit for the data were reached when piecewise linear regression was used to approximate the relationship between chlorophyll and nutrient concentrations. The regression line divided the whole data set into two regions: lower, mesotrophic (chlorophyll < 20 mg m^-3) where the response of chlorophyll to N and P was insignificant and higher, eutrophic (chlorophyll > 20 mg m^-3) within which chlorophyll yield was proportional to nutrient increments. Except for trophic type, the relationship between chlorophyll and nutrients was affected by mixing type of lakes. No significant relationships between chlorophyll, nutrient concentrations and Secchi disc visibility were found in the shallow, polymictic lakes. Possible explanations for the observed effects including resuspension and grazing pressure on algae are proposed.
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