By Antti Iho, Natural Resources Institute Finland
People’s determination is the fuel driving marine protection. The engine – innovations, technologies, policy instruments – only go so far without our willingness to strive for the common good.
Baltic Sea protection has delivered significant results in external load abatement during the recent two decades. But the sea has been shy in responding. Should we turn the steering wheel of our fueled up protection machinery slightly? Just to keep us from growing frustrated with the modest outcomes, and thereby to keep the fuel tanks loaded.
Phosphorus is the troublemaker in the Baltic Sea. External loading of algal growth boosting phosphorus started decreasing in the 1990s. Currently, the loads are about at the level of 1950s. The existing stock of phosphorus in the water, however, has been stubbornly high once brought up. The stock in the Baltic Proper hovered around some 190 000 tons before the year 1940. Currently, it is well above 430 000 tons, and seems determined to stay there. The anoxic sediments are not able to retain phosphorus. There are no improvements in sight for the oxygen conditions in Baltic’s deep waters.
Today, annual external phosphorus load amounts to about 5% of the existing stock. If all littoral countries would comply with their BSAP requirements, the share would be lowered to about 3%. The annual variation in stock driven by sediment processes is substantially higher than this change. We need to look for measures complementing external load reductions by targeting the phosphorus stock of the sea directly.
Commercial fisheries remove about 15% of annual external loading of dissolved phosphorus from the sea. There is no sustainable way to increase the phosphorus yield harvested with these fish species. However, there are fish species that are currently underutilized at the Baltic Sea level: for instance perch, pike, roach and bream. Also mussel farming might provide a new avenue for phosphorus removal from the existing stock.
This newsletter views the latest results of NutriTrade’s Pilot Mussel and Pilot Fish. They show that particularly fisheries can increase the sustainable removal of nutrients from the sea and thus provide a potentially cost-effective way to mitigate eutrophication.
Finally, nothing in external load reductions can be taken for granted: we must continue to deliver in abating nutrient from municipal wastewater treatments plants every day.