The relationship between water quality and chironomid distribution in Finland—A new assemblage-based tool for assessments of long-term nutrient dynamics

Relationship between water quality variables and distribution, diversity and abundance of sedimentary chironomids (Diptera: Chironomidae) were examined in 51 limnologically different shallow lakes in Finland. The objective was to identify which of the water quality parameters influenced chironomids the most and to explore the potential of developing a palaeoecological tool to infer past changes in water quality for the use of lake management in conservation, preservation and restoration projects. In addition, taxon-specific optima and tolerances were calculated to identify indicators for ultraoligotrophic–hypereutrophic Finnish lakes. The statistical tests indicated that the chironomid assemblages were closely related to water quality. Of the examined environmental variables total phosphorus (TP), total nitrogen (TN), colour, turbidity and hypolimnetic oxygen were the most important explanatory variables. Because autumnal epilimnetic TP had the highest eigenvalue (λ₁:λ₂) ratio, which indicates the relative significance of particular variable in explaining the variance in the species data, and lowest statistical significance level, it was considered to have the greatest potential for the development of a calibration model for quantitative inferences of past limnological conditions. In addition to the complete model, a reduced model using 41 lakes was developed that is independent of covariance with temperature. Of the tested model types, weighted averaging-partial least squares (WA-PLS) had the strongest relationship between observed and inferred TP values together with lowest error of prediction and maximum bias showing favourable model performance. In general, the results of taxon-specific indicator value showed close agreement with previous data. The results provided coherent autecological and synecological data that can be used in qualitative assessments of water quality and ecological status of lakes and most importantly as a basis for the new quantitative tool to be used in palaeolimnological studies and evaluations of TP reference conditions.