Predicting coastal eutrophication in the Baltic:: a limnological approach

Coastal eutrophication is a key environmental concern in Finland. A highly indented, well-settled coastline with a myriad of small estuaries means that eutrophication occurs at numerous localities. There is a clear need for general models that predict eutrophication across estuaries. Lake eutrophication has been successfully predicted using a combination of chlorophyll a (Chl) - total phosphorus (TP) regression models and TP mass-balance models. We applied this limnological approach to 19 Finnish estuaries. The Chl-TP regression was highly significant, accounting for 67% of the variation in Chl. When combined with a TP mass-balance equation, log observed and predicted Chl differed by 28% on average. Accuracy was improved by dividing the estuaries into those dominated by non-point-source (NPS) loading (n = 11) and those dominated by point-source (PS) loading (n = 7). A land-use regression model based on percentage of the catchment forested and estuarine mean depth then best predicted Chl in the NPS-dominated estuaries. The mass-balance approach remained the most accurate model for the PS estuaries. The land-use model and mass-balance approach are complementary tools in that their use maximizes accuracy for both NPS- and PS-dominated estuaries. This high level of accuracy demonstrates the relevance of limnological approaches to Finish estuaries.