Stormwater impact on the coastal area of the Tallinn Bay

The aim of this study is to clarify factors corresponding to spreading of algae on the investigated area and to offer solutions for the problem. For this reason water samples from stormwater outlets as well as from the coastal and open sea were analyzed against the nutrients - dissolved and total nitrogen and phosphorus. The current profile close to the Pirita river estuary was also logged during summer and fall 2012. Water sample analyzes showed that in summer nutrient concentrations in river and outlets' water are two-three orders higher than in the open bay, and that the concentration of nutrients, especially dissolved nitrogen increases with rain intensity. That means in rainy periods the nitrogen influx is increasing very rapidly due to the both reasons - greater amounts of outlets' water and higher nitrogen concentration at the same time. These data enabled estimation nutrient daily influxes through the river estuary and distinctive outlets, and last at least using a model describing the distribution of nutrients over the coastal area. It is shown that up to 95% of load is coming from the Pirita River and only 5% from the outlets, but despite this some greater outlets may play a role in algae blooms. Modeling results also indicated that the impact of storm water outlets could be eliminated by pumping the storm water further (~1 km) to the open sea. As the environmental status of the Tallinn Bay depends predominantly on the Pirita River influxes, this measure should be effective, cost effective and harmless (for the Bay) at the same time.