Reducing the phosphorus load and the algae blooms in Finnish lakes and the Baltic Sea

Abstract

Phosphorus is the nutrient, limiting algae growth in most of the lakes and rivers in Finland and therefore a reduction of phosphorus load should be carried out if algae blooms are a problem. In the Baltic Sea a reduction of both phosphorus and nitrogen has earlier been considered to be needed to reduce algae growth but recently also research papers where phosphorus has been pointed out to initially be the limiting nutrient has been published. It has been calculated that a reduction of nitrogen load by 50% to the Baltic Sea would be four times as expensive as a similar reduction of phosphorus load. Today countries in the Baltic Sea catchment area report already some success in reducing loads of phosphorus, but little for nitrogen. Thus the expensive measures to reduce load should be used in reducing phosphorus, instead of nitrogen. In Finland the first step in this work has been a proper reduction of phosphorus content in urban and industrial sewage waters. This activity started already in the 70ties. The reduction of the phosphorus load in urban wastewater is today 95%. This reduction has resulted in reduced algae (cyanobacterial) blooms in the urban wastewater affected sea areas, lakes and rivers. The second step in Finland will be the reduction of phosphorus in rural wastewater by 85 per cent to be carried out before the year 2014. The third step should be a reduction of phosphorus load from agriculture. An attempt to start this work has been made already 10 years ago when the Finnish Agri-environment Programme was established. However this program has not been successful in reducing phosphorus load, although during 1995-2004 as much as 2.5 billion has been used. It has been calculated that a chemical treatment to reduce the phosphorus content of all our field waters would not amount more than 0.07 billion /year. Therefore in our Finnish Agri-environment Programme the chemical treatment of waters from agricultural areas should be included. In this paper a low cost treatment method to reduce phosphorus content in waters from agricultural areas is introduced. If these three steps would be carried out in all the catchment countries, the phosphorus load to the Baltic Sea could be reduced to a level which it was one hundred years ago.