Sky-high phosphorus levels have been measured in the bay Högklykeviken on Gräsö outside Öregrund. In other words, it is a bay that is heavily eutrophic. However, this has not always been the case. Högklykeviken was once a spawning ground for many species of fish, with clear water and bottoms covered in dark red and bright green bottom vegetation. But about 20 years ago, everything changed. The water became turbid, the diverse bottom vegetation was replaced by eutrophication-resistant species, and fish recruitment declined sharply. Linda Kumblad and her colleagues have spent the last four years trying to find out what happened in the bay, and see if it is possible to restore the environment in Högklykeviken. But will it be possible to restore the bay, or are there some wounds that nature cannot heal?
Linda, associate professor of systems ecology at Stockholm University’s Baltic Sea Centre, and project manager for Thriving bays at BalticWaters, walks along the 300-meter-long canal leading from the sea into Högklykeviken. In the canal, an excavator on a barge is emptying bucket after bucket of crushed rock onto the canal bed.
‘When we arrived here in 2020, our first thought was that the eutrophication in the bay was due to nutrient leakage from land. After several years of sampling and analysis, it turned out that our hypothesis was wrong,’ says Linda.
The excavator drops another load of stones into the water. Håkan Andersson, from GL-sjöentreprenader, operates the excavator while his dog Gorm stands in the bow and looks out over the bay.
Left: The boat with crushed stone. On the right: Håkan operating the excavator. Photo: Linda Kumblad
Gorm the dog. Photo: Linda Kumblad
‘Our investigations show that it is very likely that erosion in the canal is the main cause of the turbid water and the high phosphorus content in the bay,’ says Linda.
About 25 years ago, the channel connecting Högklykeviken to the Baltic Sea was dredged. The dredging exposed layers of clay further down in the sediments, while increasing the water flow in the channel. The increased water flow still, to this day, brings particles and nutrients from the exposed clay layer into the bay and increases eutrophication and turbidity.
The crushed stone that Håkan, with a watchful eye from Gorm, is placing along the edges of the canal and on the bottom will prevent the water from washing over the exposed clay surfaces, thereby reducing the influx of nutrients and particles into the bay. It is not a complicated measure, but it is not done overnight. It requires a shoreline protection permit, a notification of water activities and approval from water and landowners. And it costs a lot.
A satellite photo from 2009 clearly shows the turbidity in the canal and how the milky, muddy water spreads into the bay, but also outside the estuary and into the surrounding waters. Source: Google Earth Pro, 2009
‘Perhaps the most important lesson is that dredging can have unforeseen, negative consequences on the environment. Restoration can be difficult, and the costs can be very high. It is therefore important to gather knowledge about the environment and conditions and carry out a risk assessment before dredging,’ says Linda.
Uppsala County Administrative Board has contributed with funding for the measure. Malin Hjelm is a nature conservation officer at the Uppsala County Administrative Board and believes that the project will be important for the region.
‘Many shallow bays in Uppsala County have been negatively impacted by dredging and other human activities and there is a need to develop and test possible methods to restore these important habitats. We support the project in Högklykeviken because it can contribute valuable knowledge and experience in the continued restauration work,’ says Malin.
The work also takes time. Håkan is almost halfway through the seven-week process of placing crushed stone in the canal.
But this measure, so called “erosion protection”, is not the whole solution. In May this year, an aluminum treatment started in the bay, to bind the phosphorus that has accumulated over the years. Reducing erosion from the canal into the bay is the main problem, while the goal of the aluminum treatment is to clean up the mess made by the dredging over the years.
‘We hope that the erosion protection in the canal will reduce turbidity and nutrient inputs to the bay. At the same time we are doing an aluminum treatment in the bay. The result will hopefully be clearer water, more bottom vegetation and fish,’ says Linda.
The boat mixes an aluminum solution into the sediments. The aluminum binds a large part of the nutrient phosphorus in the sediments, instead of being dissolved in the water and driving eutrophication. Photo: Linda Kumblad
And the vegetation is crucial for fish spawning. Today, fish migrate into the bay in the spring, but reproduction is not very successful due to sparse bottom vegetation. Both perch and pike depend on bottom vegetation, both in the egg and fry stage, and clearer water is a prerequisite for sunlight to reach the bottom so that the bottom vegetation can grow there – as it did in the past.
Chara baltica
Agneta Loge André has been staying at her family’s summer cottage in Högklykeviken since the 1950s.
‘When I was a kid, we had a boat with a little spinner. When we set out, mom, dad and three children, we competed to see who would be in the bow, where you could see how the fish scattered in front of the movin boat. On the bottom, the sand glittered. Today it is not like that. We are very happy about what is happening now in the bay, this project,’ says Agneta in an interview in Dagens Nyheter earlier this year.
The dredging of the canal has also changed the natural threshold in the mouth the bay. Natural thresholds limit the inflow of water into the bay and allow the water to warm up faster during spring and summer, which is important for fish reproduction. However, this is not something that erosion protection can solve.
‘We will probably not be able to restore Högklykeviken to its former glory. Our goal is to overcome eutrophication and turbidity, and regain good water quality in the bay. The solution must also work for those who live and spend time in the bay to be sustainable in the long term. Here in Högklykeviken, together with residents and Uppsala County Administrative Board, we have come to the conclusion that the erosion protection in the canal in combination with the aluminum treatment is a good solution,’ says Linda.
With the new restoration regulation, the pace of action to improve the environment in the coastal areas of the Baltic Sea will hopefully increase. Then it is very important that the restoration carried out actually has an impact. That the right action is taken in the right place. And here it is crucial to find out the root problem and fix it, otherwise we risk doing measures and using resources that have little or no benefit. Even if the right local measures are done, we must not forget the big picture.
‘There is no getting around the fact that we must continue to work to reduce eutrophication in the Baltic Sea as a whole, especially with measures on land that reduce nutrient leakage to the sea. And large-scale, unsustainable fishing must stop. Everything is connected, from the open sea to bays like Högklykeviken,’ says Linda.
So what is the answer, can wounds from dredging be healed? The question has no clear-cut answer. In the case of Högklykeviken, the environment in the bay will probably not be able to return to what it once was, but it should be able to become much better. But one thing is certain: we should think once and twice before carrying out dredging.
How will we know if the measure is successful?
It won’t happen overnight. Measurements have been taking place in the bay since 2020, and many will continue until 2026. In the bay, loggers measure turbidity, light, temperature and salinity every hour throughout the year. In addition, scientists take water samples about once a month to obtain information on changes in water chemistry (water quality). Once a year, vegetation and fish in the bay are also examined. In addition, parts of the bottom of the canal are examined to measure whether vegetation also spreads there after the erosion protection has been in place for a while.
More about Thriving Bays
The aim of the the project is to try to show that it is possible to improve the environment in shallow bays and to develop knowledge about how this can be done in a cost-effective way. The project will work to test and evaluate individual measures in a number of case studies, and full-scale restoration in some shallow bays along the Svealand coast will be carried out. Thriving bays runs until 2027 and is implemented and financed by BalticWaters with financial support from, Stockholm University’s Baltic Sea Centre, the Stockholm County Administrative Board and the Uppsala County Administrative Board . The Swedish Agency for Marine and Water Management has allocated funds to Stockholm University for the implementation of sampling and monitoring in the project bays.
