Photo: Enno Hallek

Features TOO MUCH NITROGEN OR TOO MUCH PHOSPHORUS? CONTROVERSY IN BALTIC waters

Scientists have not always agreed on either the causes or the possibility of restoring the cloudy, fish-poor, partially oxygen-deficient, algae-blooming, oil-slicked Baltic Sea. Wherein lies the disagreement? There seem to be two main controversies: 1. The Baltic Sea is eutrophic. Or is the Baltic Sea not eutrophic? 2. Algae blooms are controlled by the nutrient phosphorus. Or is the bloom controlled by both phosphorus and nitrogen?

Published in the printed edition of Baltic Worlds BW 3 2011, p 12-14
Published on balticworlds.com on October 3, 2011

“It is the sunrise I remember, and the sunset, the strong light over the sea”, says Enno Hallek, who has, with greater mastery than most, captured the soul and colors of the Baltic Sea in his paintings.

As a little boy, he lived half the year on his father’s fishing boat in Estonia, where the fyke net gathered the catch into the well in the middle of the boat. The entire family lived in the slim, agile vessel, which his father had built with his own hands, the boat that in the 1930s had taken them to Finland and Sweden to sell eels as far in as Slussen, the lock that separates Lake Mälaren from Saltsjön, the Baltic, right in the middle of Stockholm.

Enno has seen the sea, the green sea teeming with fish, and since reaching adulthood has been concerned about what happened to life in the sea in the last century. This is within Enno’s living memory, and that of many others.

So, what happened? Scientists have not always agreed on either the causes or the possibility of restoring the cloudy, fish-poor, partially oxygen-deficient, algae-blooming, oil-slicked Baltic Sea.

Wherein lies the disagreement? There seem to be two main controversies:

1. The Baltic Sea is eutrophic. Or is the Baltic Sea not eutrophic?

2. Algae blooms are controlled by the nutrient phosphorus. Or is the bloom controlled by both phosphorus and nitrogen?

There is another core question: Can the Baltic Sea return to the ideal status it had around the middle of the last century?

In addition, there are the questions having to do with the Baltic Sea biota: seals, fish, zooplankton, phytoplankton, and bacteria. As well as the fact that the sea is being polluted by things other than nutrients: primarily industrial discharge, and environmentally hazardous shipping. Then there is the problem of overfishing.

To approach the issue of the health of the Baltic Sea, you have to consider essentially all these components. But if you start with the question related to the amount of nutrients in the sea — whether the Baltic is eutrophic or not — you must first agree on a time frame. The Baltic is a young sea, which was for long periods quite deficient in plant nutrients by its nature — oligotrophic, to use the technical term.

During the last hundred years, the anoxic seabeds have increased five-fold: they now take up an area the size of Denmark. In chemical terms, oxygen deficiency on the seabed is an on/off switch for more nutrient-rich conditions. The explanation is that when dead organic material sinks down to the bottom, it should preferably encounter a healthy, oxygen-rich environment, where the material is converted to sludge, nutritious sludge.

When the surface of the seabed lacks oxygen, the precipitated organic material will essentially rot instead. Chemically, this means the nutrients will not remain in the bottom sediment — phosphorus will be released and carried up into the body of water again.

What creatures want this nutrient enrichment? The only types of organism that can absorb nutrition in this form are phytoplankton and algae along the shores. The sea becomes a billowing smorgasbord for species after species to thrive in. Green algae and cyanobacteria (formerly called blue-green algae), for example, eat until they die and in turn sink down to the anoxic seabeds. This goes on all summer, and as soon as the sun peeks out after the ice breaks up, it is time for the next spring bloom.

Where do the nutrients come from? From us. In the last hundred years, phosphorus and nitrogen have been flowing out, ever faster, from toilets, agriculture, and livestock farming, along with nitrogen pollution from vehicle traffic and combustion. We have some control over sewage when it is routed through waste treatment plants, but it isn’t treated everywhere.

That the Baltic has become more nutrient-rich is beyond doubt. The question is whether it can be called eutrophic or whether it is out of balance in relation to its former self. A hundred years is nothing in the life cycle of the Baltic Sea. But everything we have done in the last hundred years to improve crops, transportation, heating, and urban hygiene, and to expand livestock farming — all of this is doubtless a burden on the Baltic, which has been reshaped.

We must reduce the nutrient load — that is the theme of the second distinct controversy.

Is there too much phosphorus? Or nitrogen? Should waste treatment plants be expanded to deal with nitrogen as well? Is the whole thing due to traffic, which loads nitrogen pollutants in exhaust fumes? Should waste treatment be required only of the big cities? Or is the problem the uncontrolled — and perhaps uncontrollable — diffuse emission sources that here, there, and everywhere ooze out their nutrients into the nearest straightened watercourse, which in turn delivers them swiftly and efficiently to the Baltic? Might the problem be the straight, dredged, and drained rivers and streams that no longer work as natural water purification systems, as a winding river does?

First: nitrogen versus phosphorus.

Proponents of expanding phosphorus treatment and ignoring nitrogen base their arguments on the following: The phosphorus content is stable in the water. It cannot be eliminated naturally from the water or the bottom sediment. However, it is easy and relatively cheap to treat wastewater to remove phosphorus.

Nitrogen purification, on the other hand, is an expensive process, one where we also encounter the problem that nitrogen moves chemically between air and water. Certain plants, such as cyanobacteria and land plants like beans and peas, do not need to be served nitrogen in the water or the soil. They can take nitrogen out of the air themselves — they are nitrogen fixers. Thus, some scientists argue that there is no point investing in nitrogen purification of sewage. All we need is massive separation of phosphorus to restore the nutritive balance of the Baltic Sea.

But this happy news does not hold up to scrutiny. The argument is far too simplified according to Rutger Rosenberg, professor of marine ecology with Marine Monitoring in Lysekil on the west coast of Sweden.

The thing is, the Baltic Sea does not behave the same way all year round and in all the subregions. In the spring when the ice breaks up, the Baltic Sea proper is packed with both nitrogen and phosphorus and the spring bloom explodes — it blooms, and wilts, sinking to the bottom. Afterwards, there is no more accessible nitrogen in the water, but some phosphorus is still there and additional phosphorus seeps out from the anoxic seabeds — and so it is time for a massive bloom of cyanobacteria, nitrogen-fixing blue-green algae, instead. However, there are very few nitrogen fixers in the saltier regions of the Baltic: the Danish straits and the Kattegat (see map).

The importance of nitrogen purification is thus seasonal and regional: it is least important in the northern Gulf of Bothnia, and considerably more important in the southern parts.

Professor Fredrik Wulff of Stockholm University adds:

“If the spring bloom can be reduced by lowering the nitrogen content of the water, less organic material will sink down to the seabeds, resulting in anoxia. But the connections are complex and difficult to describe in simple terms. In addition, the Baltic leaches nitrogenous water into the Kattegat, which is highly undesirable. Increased nitrogen content there causes other blooms than blue-green algae.”

This controversy has begun to wane; the need for nitrogen purification is more widely accepted today, with certain exceptions. But it is not enough to concentrate efforts on urban waste treatment plants and skip the extremely neglected issue of fertilizer and livestock farming in the eastern Baltic countries. Waste from cows, pigs, chickens, and people also play in different emissions leagues, so to speak. Emissions from people, all 85 million of them around the sea, are significantly lower than emissions from animals. Farmyard manure combined with commercial fertilizers used on the fields account for the bulk of the nutrient supply to the Baltic Sea.

And the Baltic is not a single water area. It is divided into three parts: The Gulf of Bothnia, the Gulf of Finland, and the Baltic Sea proper, which all have different depths and salinity. There are shallows between these areas that limit the exchange of water and nutrients between the basins, but also deep sea trenches that are hardly touched by surrounding movements. The inflow is from two directions: from freshwater rivers, and from the south in completely unpredictable deep-water currents of saltwater from the Kattegat. The body of water is always layered, with a more saline sub-surface layer and a brackish surface layer. This is one of the reasons the deep trenches are almost always anoxic in the deepest parts. But increased nutrient loads and plankton blooms during the last century have caused the drastic expansion of shallower anoxic regions as well.

Everyone who works with the Baltic Sea knows this — it is a highly complex system that scientists have been trying to model ever since computers allowed such large calculations.

With a grant from the Ministry of the Environment in Sweden, Fredrik Wulff has been able to expand on his previous success in modeling the Baltic in the Mare Project. He has now been able to establish the Baltic Nest Institute (BNI), located at Stockholm University, where predictive modeling is being done.

Fredrik Wulff:

“One of our first assignments was a job for HELCOM, the Helsinki Commission. How much should the nutrient loads be reduced to restore the environment? How should the load reductions be allocated among the different countries? Along with my colleagues and using the models and databases we have developed, I was able to perform these calculations, which HELCOM included in BSAP (Baltic Sea Action Plan), which was signed by all the countries in Krakow in November 2007.”

If we go back within living memory, that which tells us what the Baltic was like during the last century, the fishing is what we remember. It was so easy to reel in a beautiful pike for dinner, the codfish banks bubbled with life, the fishing boats landed laden with their catches. We all know how the discussions about cod fishing have sounded, how fishing quotas have been exceeded, how the eels have disappeared — what happened?

Everything is connected. Take cod for example: Cod cannot reproduce in the Baltic Sea without sufficient highly saline water. Inflow of salty water from the Kattegat is necessary, since cod eggs develop suspended in a water layer between the saline bottom water and the merely brackish surface water. If the salty, oxygen-rich inflows from the Kattegat are absent for too long, the eggs do not survive: they die of lack of oxygen and too low salinity.

The annual successful reproduction of cod is thus somewhat uneven, which is not a disaster as long as the fishing pressure is moderate. When it increases, and the market prefers large fish, the parental generations of cod that are the source of regeneration vanish.

The cod is our sea’s top predator fish — it is at the top of the food chain. It eats the sprat that we do not want. When the cod decline in number, we have an excess of sprat, which devour all the animal plankton upon which many other fish depend. The balance is disturbed. No other creature will eat sprat, it is too pointy. Zander (often called “pikeperch”) and pike prefer herring, and suddenly the herring decline as well.

Everything is connected. And with its low salinity, the Baltic is a more sensitive environment than most. Baltic Sea researchers at the Swedish Environmental Protection Agency’s Marbipp Project on marine biodiversity compared the species-rich North Sea to the species-poor Baltic and determined that species loss is considerably more severe in the Baltic:

“If you eliminate a species on the west coast of Sweden (such as the blue mussel), it might be analogous to losing one letter of the alphabet, while on the east coast it would be like losing a large chunk of the language.”

It could be that the cod is on the way back, helped along by fishing regulations that, this time, have met with better compliance. But this is, as said, just one example of the difficulties involved in keeping the Baltic Sea in balance. As for the eel, it seems to have given up hope for the Baltic. This is partly the fault of the hydropower plants, where the silver eel have been caught in the turbines for many years — but the main problem is probably the grotesque overfishing of elvers along the entire coast of Europe. They do not even make it up to the Baltic.

Another problem is that the sea has been fouled with substances that stay in the animals, and plants, and are stored in the bottom sediment. Organic chlorinated substances of various kinds, of which the most well-known are DDT and PCB, which destroyed seal reproduction, bullhead skeletons, the protective wreath of the seaweed belt around newborn life on the shore, and the sea eagles that took their sustenance from the sea. These particular problems are slowly declining, or being embedded in the sea floor, but new substances are always threatening — fire retardants are one of the current concerns.

But what we see, and what we react to, are the plankton blooms. It is that repulsive soup of algae and cyanobacteria that thwarts life in the archipelago in summer, invasions that are not predictable and about which it seems nothing can be done. A warmer climate does not help the situation — on the contrary. So, where should we start? Is there something wrong with the joint international action plans? What is required of the nine coastal nations and the 85 million people who live in them for visibility to improve in the Baltic and the balance to be adjusted?

What we can say is that the focus of the problems is changing. While the coastal city of Kaliningrad is still dumping all of its sewage into the Baltic untreated, it looks like the waste treatment plant in St. Petersburg will, with outside help, soon be finished. And waste treatment plants are being expanded in Poland as well.

What has been added to the mix is the voluminous growth of intensive agriculture and livestock farming around the coast and along the rivers, which are adding nutrients to the sea, completely uncontrolled. Fredrik Wulff estimates that this will become the predominant addition within ten years. Opportunities to use the large manure volumes for energy production are as yet unexploited.

Engineers have suggested various large-scale technical methods in recent years for addressing the problem of dead seabeds in the open Baltic Sea. A project called “Simulation of the effects of some engineering measures aimed at reducing effects from eutrophication of the Baltic Sea” used modeling programs to test some of these measures.

A report signed by Rutger Rosenberg and Anders Stigebrant, head of the Marine Systems Analysis Group in Gothenburg, is expected in the autumn of 2011. It will assess the effects of pumping oxygen down into the Bornholm trench and the Gotland trench. Wind-driven pumps are one idea for making a costly project of this kind possible.

In the future, deepwater oxygenation of the Baltic may make it possible to stabilize cod production, for which there is such high demand.

But can we return to the Baltic Sea as it once was within living memory? Enno Hallek’s father did not give up until he was very old. After the Russians invaded Estonia during the war, they scuttled his boat so that he could not leave the country. When the Germans later held the country, he salvaged the apple of his eye from where it lay beneath the ice, repaired it — and fled Estonia with his family in 1943. And he kept fishing, though now in Blekinge in southern Sweden, where he built yet another boat of the right size for eel fishing in Hanö Bay. But the eel was already on the decline — something Enno sees as his wake-up call to what was happening in the Baltic. His pictures are testimony of his love for his polluted sea and his yearning for change.

“Can we have a cleaner sea?” I ask Fredrik Wulff.

“Of course we can, if the political will is there”, he answers. “But that will require a different kind of agriculture, which will result in higher food prices.”

Are we ready for that? ≈

Ann-Louise Martin