An Algorithm for Assessment of the Water Purification by Seaweeds: An Application for a Black Sea Recreational Coastal Area

Discovering the capability of seaweed communities to cope with the human impact is among the environmental problem-solving approaches which aim to restore the quality of coastal habitats. Usually, it involves carrying out complex investigations, a large volume of data and process modeling. This paper introduces a simplified algorithm for calculating the seaweeds water purification capacity, which connected with the absorption of the inorganic nitrogen (N) and phosphorus (P) fed into the coastal waters by sewage and that of recreational sources. The algorithm involves the collection of data on species composition and stocks of macrophytes, calculating the value of N and P inflow into the coastal waters, the daily value of these elements potential extraction by seaweeds and calculating the self-purification index (SPI) suggested by us. At SPI < 1 the seaweeds are potentially capable to fully extract N and P from the incoming sources, and at SPI > 1 a partial purification of coastal waters from the above-mentioned nutrients takes place. The results of applying the algorithm in the coastal waters affected by recreational load near Sevastopol (southwestern Crimea) demonstrate that the bottom vegetation is capable of fully removing of the inorganic nitrogen (SPI_N = 0.026) and phosphorus (SPI_P = 0.044) during the period of maximum recreational pressure (3000 people/day). The suggested algorithm can be used for the water quality monitoring and management of the coastal areas with a high anthropogenic and recreational load.