Abstract
Nutrient over-enrichment of the Baltic Sea, accompanied by intensified algal blooms and decreasing water clarity, has aroused widespread concern in the surrounding countries during the last four decades. This work has used a well-tested dynamic mass-balance model to investigate which decrease in total phosphorus loading would be required to meet the environmental goal to restore the trophic state in the Baltic Sea to pre-1960s levels. Furthermore, the extent to which various abatement options may decrease the phosphorus loading in a cost-effective manner has been studied. Upgrading urban sewage treatment in the catchment could, alone or in combination with banning phosphates in detergents, be sufficient to meet the set environmental goal, at an estimated annual basin-wide cost of 0.21–0.43 billion euro. Such a plan would potentially decrease the total phosphorus loading to the Baltic Sea with 6,650–10,200 tonnes per year.
Highlights
Eutrophication as a result of anthropogenic over-enrichment of nutrients is a major environmental concern around the Baltic Sea, Northern Europe [1,2]
Of the variety of different total phosphorus (TP) models for the Baltic Sea, CoastMab, which will be used here, is the only published TP model which fulfils all of the following criteria [6]: 1) it takes into account all major TP fluxes to, from and within the Baltic Sea, 2) it has a unitary set of model constants and equations; i. e., these are the same for all basins, and 3) it gives good predictions of TP concentrations in all of the major basins of the Baltic Sea (Figure 1)
Simulations with the CoastMab model showed that 6,650– 10,200 tonnes of TP would have to be removed from the annual loadings to meet this goal; i.e., to increase the Secchi depth in the Baltic Proper with 45% during the summer months
Summary
Eutrophication as a result of anthropogenic over-enrichment of nutrients is a major environmental concern around the Baltic Sea, Northern Europe [1,2]. An early estimate from Larsson et al [4] indicated that the TP loading had increased by a factor of 8 since before the 20th century. The development of dynamic nutrient models allowed Schernewski and Neumann [5] to conclude that the loading had increased over the past century by a factor of 4.5, while Savchuk et al [2] calculated a three-fold increase. Hakanson and Bryhn [6] presented the first dynamic TP model with a unitary set of calibration constants which delivered good predictions for all of the five major basins of the Baltic Sea (see Figure 1), and estimated that the TP loading had increased with about 50%
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