Eutrophication: ugly word, awful effect

Surnud alad Läänemeres kasvavad.


The word is enough to scare away a most dedicated reader. But hey, wait! The term does relate to our diet.

Fewer fish, less nice sandy beaches, more of the summertime blues of blooming Cyanobacteria. At that, scientists are rather pessimistic: over the past half century, the damage done to Baltic Sea is irreversible. 

Already, at the bottom of said sea, vast areas lack life as there is no oxygen. And, paradoxically, oxygen is lacking because people have «overfertilized» the Baltic Sea with nitrogen and phosphorus. With benthic fauna lacking, there’ll be no fish – at least not the kind we are used to.

Directly or indirectly, eutrophication is dealt with by hundreds of scientists in Baltic Sea states, one of them being Prof Erik Bonsdorff of Åbo Akademi, Finland. The man researches effect of nutrients on the Baltic Sea within a project called COCOA. In their research, the scientists are attempting to go deep.

«With oxygen in a sea, there’s circulation – sea animals constantly ventilate the system,» explains Prof Bonsdorff. «From the surface, they bring oxygen into the sediments, and in their turn keep the benthic fauna alive.»

Treatment no good

The tiny creatures living in the seabed mud aren’t just food for the fish; also, they serve to re-mineralise it and maintain a certain level of oxygen at the bottom of the sea. 

The Baltic Sea states and even Russia have done a good job managing such pollution, flowing forth from cities. Thus, the vast city of St Petersburg by now possesses a sewage treatment system from whence very clean water finally reaches the sea. In spite of that, nutrients still flow to the sea in amounts too abundant – the chief polluter being agriculture using lots of phosphorus and nitrogen rich mineral fertilisers.

Regrettably, even hearty cleaning cannot restore what has already been lost – according to Prof Bonsdorff, treatment can’t restore the oxygen circulation that the sea no longer has.

The scientists have also considered artificially pumping oxygen into the sea-bottom; alas, this would make matters worse – by stirring up the hazardous sediments, especially of phosphorus. 

«As oxygen content goes down, then we’re no longer just talking about sea bottom or the various layers of water; it will also be reduced in the air above the sea,» says Prof Bonsdorff. «Pumping oxygen into the bottom of the sea will bring more harm than good.»

By today, the flow of nutrients into the Baltic Sea is a lot smaller than in 1970ies; still, the sea is rather heavily polluted. «Also, farmers in several Baltic Sea states have again started to more abundantly use mineral fertilisers which enhance eutrophication,» says the professor.

According to Prof Bonsdorff, due to lack of oxygen the seabed already misses 300,000 tonnes of biomass, which otherwise would serve as fodder for the fish. All told, we will miss out on huge amounts of fish.

At that, the scientist does not seem to have much faith that the Baltic Sea clock could be turned back at all. «Eutrophication is continuing in spite of the reduction of the nutrients that end up in the Baltic Sea,» he admits. «The T is crossed by climate change.»

According to the scientist, circulation of oxygen is also impacted by overfishing, which is now more or less under control.

«The amount of all the other problems impacting the Baltic Sea is ever increasing. For instance: lots of sea creatures depend on ice,» says he. «If the sea fails to ice up in winter, lots of organisms say thanks and good-bye.»

The last ice age ended over 10,000 years ago and, according to Prof Bonsdorff, the organisms currently dwelling in the Baltic Sea have been acclimatising for millennia.

«Now, however, the conditions changed over a few decades,» he says. «If at all we are hoping for things to get better, we’ll have to wait for decades. And even then climate change might not spare our native sea.»

On a map, Prof Bonsdorff points to the sea areas painted black where no-one lives at the bottom, having no oxygen to breathe. The grey areas are the critical areas, oxygen-wise.

Denmark plus Estonia

«By today, the dead Baltic Sea area ought to be about 90,000 square kilometres, the size of Estonia and Denmark put together. It all happened in 110 years and there’s no basis to hope we can solve the problem in a couple of dozen years,» he says.

No longer contained to the depths of the sea, oxygen scarcity is nearing the shores. In 40 years, Baltic Sea medium temperature has risen by 1.8 degrees; over the next 50 years, it will add two more degrees. «Warmer water and ever less oxygen – that’s a recipe for a dark future for the sea,» notes the professor.

«Not easy to turn time around,» he continues. «Obviously: whatever we might do to improve the Baltic Sea, its ecosystem will never be quite what it was before. No silver bullet to kill the problem.»

Summing it all up: we will have to be reconciled to eating other kinds of fish. For instance, forget about the seabed loving codfish. «We’ll be eating Norwegian salmon,» Prof Bonsdorff prophesies, ironically.

According to Prof Kari Hyytiäinen of Helsinki University, it is indeed the very agriculture that pours the bulk nutrients into the Baltic Sea, using artificial mineral fertilisers.

«Nutrients are also brought to the sea by living organisms; but looking at historic levels regarding the Baltic Sea, these were four-five times lower than in 1980ies – thus, we mostly have to do with the effect of human activity,» says he.

The author participated, at the invitation of Finnish foreign ministry, in meetings and seminars arranged within Gulf of Finland Year.