Littoral countries have managed to decrease external nutrient loads to the Baltic Sea. Current phosphorus loads are at about the levels of the 1960’s but water quality improvements lag behind. We should not get frustrated with the sluggishness of the sea and the occasional setbacks. We must keep delivering the current abatement measures and be innovative but risk averse in developing new ones.
The Baltic Sea has always had a feature making it prone to the occasional mass blooms of algae. It has a strong halocline, a layer with more saline and heavier water below and the lighter, less saline water above it. The vertical movements of water are almost blocked by this layer. It thus hinders the effective transport of oxygen-containing water to the bottom areas. There, oxygen would be needed as the microbes decompose algae and want to breathe. If there’s no oxygen they shift to alternative elements and molecules willing to accept the extra electrons they’re left with, after their decomposing activities. This, after some elusive biogeochemical rounds, leads to benthic release of phosphorus, a process also known as internal loading.
We have every reason to be unhappy about the apparent change in the salt pulse pattern.
Getting salty, heavy, oxygen rich water via the Danish Straits alleviates the oxygen deficit of bottom waters but at the same time strengthens the halocline. In the old days, the salt pulses – or Massive Baltic Inflows – were more frequent. Until about 1980 there were from 5 to 7 MBIs per decade. The inflow of oxygen was frequent enough to prevent large areas of anoxic bottom areas from emerging.
After 1980, the rate of salt pulses has dropped to about one per decade. This is enough to keep the halocline strong but not enough to import sufficiently oxygen. After an MDI, there is oxygen for a while for microbes to dispose of their electron waste to. But this comes at the cost of following season’s oxygen supply as the halocline gets stronger. The internal loading increases and remains on a high level. Salt pulses have turned from a vital oxygen maintenance process into the Baltic Sea occasionally peeing itself when cold: helps at first but after a while things are even worse. We have every reason to be unhappy about the apparent change in the salt pulse pattern. But there’s nothing we can do about that.
So what can we do?
We need to curtail nutrient loading even further.
we need to carry on the good work we already do. Point sources need continuous efforts to maintain the high level of abatement: new cohorts of engineers must be educated, motivated and payed; abatement capital maintained and reinvested. We need to keep paying for the high abatement levels every day. Remember this when you cast your vote the next time. Point source nutrient management is a matter of political will.
we need to bring all point sources on a par with the best ones, whether they are located in the littoral countries or in, for instance, Belarus. Cooperate, invest, try to forget the country borders. I wouldn’t be surprised if the lowest hanging fruits were already picked by modernizing the point source abatement in the eastern Gulf of Finland – but then we need to move on to the second lowest ones, requiring a bit more effort and yielding a bit less of improvements.
we need to see if there’s something to be done with the existing stock of nutrients, either in the water body or in the sediments. Can fisheries targeting currently un(der) harvested species provide inexpensive and sustainable nutrient removal? Are there ways to bind phosphorus to sediments by means of artificial oxygenation, or by massive additions of some other natural substances like marl or simply clay particles? While being innovative, we need to be careful. Conducting large scale experiments is expensive and difficult, but necessary to safeguard us from the unintended consequences of our benevolent conservation actions.
even an incremental decrease or increase in per hectare nutrient loading from food production translates into big total changes at the Baltic Sea level. As it is the biggest anthropogenic source, we must keep on addressing nutrient loading from agriculture. But here, too, we need to be careful. A decrease in, say, nitrogen loading must not occur at the expense of increasing phosphorus loading or vice versa. The desire and need to reach further abatement must be kept in check by realism and scientific scrutiny.
a word of warning. The Baltic Sea did pee itself in 2014 and 2015. After a chain of unlucky events, this will be felt in the pants of Gulf of Finland. The phosphate concentration in the surface water is very high, likely to result in lots of algae in the summer 2017. Maybe we should hope for a cold and stormy summer?