An analysis of catchment factors associated with heavy metal export into the Baltic Sea and nature-based solutions aimed at its limitation

The aim of the article was to determine the shares of individual Baltic countries participating in the inflow of metal loads to the Baltic Sea and identify patterns of similarity between these countries regarding the causes of heavy metal load generation. The analyses used HELCOM and EUROSTAT data. The findings indicate that Finland and Sweden generate the highest total loads of heavy metals flowing in through rivers. However, Lithuania and Finland are distinguished by high metal loads calculated per km² of catchment area. Clustering countries in terms of their similarity in the heavy metal loads provided to the Baltic resulted in three groups. Finland and Lithuania generates the highest mean loads of cadmium, chromium, nickel and zinc per unit area [kg/km²/year]. Estonia and Latvia generates the highest mean annual loads of lead, mercury and copper. Poland, Germany and Sweden generates the lowest heavy metal loads. Multidimensional data analysis showed a strong correlation between aquaculture production in the Baltic Sea catchment area, the number of cattle, beef, mutton, pigs, poultry, and meat produced from them, the amount of waste, trucks, cereal production, the use of nitrogen fertilizers, and the loads of heavy metals reaching the Baltic Sea with river waters. Therefore, there is a need for continuous monitoring of the loads and transfer of heavy metals to the Baltic Sea, and for activities aimed at eliminating them from the environment. For this purpose, Nature-Based Solutions can be used, as they represent inexpensive, nature-friendly methods for removing pollutants from surface waters.