Seven-year project shows that eutrophic coastal areas can be saved
By reducing the nutrient load from land and addressing the internal load, eutrophic bays along our coasts can be saved. But the applied measures have to go hand in hand, according to the researchers behind the scientific demonstration project Living coast, which is now presenting its results.
Text: Henrik Hamrén
Photo: Joakim Odelberg
Björnöfjärden in Värmdö Municipality was previously one of the most eutrophic bays in the Stockholm archipelago. But today, seven years and several million SEK later, the Living coast project has turned this trend. The water in the bay is now much clearer, the seabed is better oxygenated and plant and animal life is recovering.
“The objective of the whole project was to show that, by applying the right measures at the right place, a good ecological status can be restored to coastal bays and inlets,” says researcher and project manager Linda Kumblad.
Reducing the nutrient load from land
Together with her research colleague Emil Rydin, she published a white paper, that describes in detail how they went about cutting the eutrophication in half and recreating the good ecological status in the bay.
“The greatest challenge was reducing the nutrient load from agriculture, horse farms and homes with poor toilet waste treatment systems,” says Emil Rydin.
Many long meetings were needed with the area’s residents, including land owners, horse keepers, farmers and boat clubs, to try to convince them of how important it is to invest in treatment system of private sewage, for example.
“For private property owners, improving waste water treatment systems costs a lot of money, which made it harder to motivate many of them,” says Linda Kumblad.
Reducing phosphorous emissions from bottom sediment
The largest leakage of phosphorous did not come from the land, however, but from earlier phosphorous emissions that had been stored in the bay’s bottom sediment, the so-called internal load. The project consequently also invested in aluminium treatment, which means that the phosphorous is bound to and stays in the sediment.
The aluminium treatment not only provided clearer water and greater water transparency, but also made the residents more receptive to other measures within the project.
“Once the improvements became visible in the water, when people actually saw that it became better, their motivation also increased for implementing other measures, such as investing in improved waste water treatment systems. It was very tangible,” says Emil Rydin.
Important to motivate the local population
The project’s broad approach to addressing the leakage from all nutrient sources in the catchment area also contributed to increasing people’s motivation, Linda Kumblad adds.
“They saw that it was not just those with poor drainage who would contribute, but that everyone would make an effort,” she says.
The aluminium treatment was the most controversial measure and over the years has met with some scepticism, mainly from other researchers.
“They were mainly afraid that the measure against the internal load would take focus from measures on land,” says Linda Kumblad.
Both of the types of measures must go hand in hand...
According to her, it is necessary to stop the internal load, through aluminium treatment for instance, if it is to be possible to see a positive effect in one’s own bay locally within a few years. Solely measures on land are then often not enough since the internal load is so dominant.
...and applying both of the measures at the same time is best.
“One cannot be satisfied with just the aluminium treatment. Rather, measures to restrict the nutrient load from land at the same time are necessary, otherwise the water will soon become eutrophic again. Both of the measures must go hand in hand,” says Linda Kumblad.
There are now more fish in Björnöfjärden than there were seven years ago and the water is significantly clearer.
The Living coast project was initiated and is financed by the BalticSea2020 Foundation. The total cost is estimated at just over SEK 50 million. But far from all of this money went to paying for the actual measures. An important part was also taking tests and conducting studies to be able to evaluate and document – and to calculate what measures are the most cost-effective.
“The measures to reduce the nutrient load from horse farms and private waste water were the most expensive. The least expensive efforts were to stop internal load with aluminium treatment and liming of farmland,” says Emil Rydin.
Eutrophication can be reduced locally with aluminium in sediment and measures on land
It is hoped that the project’s white paper will inspire more effective remediation work throughout the Baltic Sea region.
“What we have done in Björnöfjärden can be done in a large number of other places,” says Linda Kumblad, and continues:
“To obtain a visible effect locally, the measures must be done together, in an entire catchment area and around a bay that has a limited water exchange.”
The researchers’ advice is to focus remediation work in smaller and delimited areas where one can see positive effects relatively quickly and clearly.
“And when one sees that the measures yield results, it hopefully leads to further remediation work that in the long term will have a positive effect not only on the local environment, but on the entire Baltic Sea,” says Linda Kumblad.
After seven years’ work, she and Emil Rydin have gathered a number of different experiences and new knowledge in terms of working locally with anti-eutrophication measures.
Perhaps the most important conclusion they draw is that remediation work against eutrophication is difficult – and that it requires both patience and a long-term approach.
“Another important conclusion is that restoring a good ecological status and a good marine environment in enclosed bays is actually possible.”