Rebuilding the Abramsen River: Interview with Vebjørn Opsanger

Located in the European Reconstruction Area Swedish Lapland The Abramsån River is Europe's longest undammed forest river, a tributary of the 210-kilometre-long Råne River and a wild landscape. This is typical of many waterways in northern Sweden that have been damaged by historical logging.

2023, Rebuilding Sweden team Started working hard Restore the wildness of the Abramson Reach by restoring the river's natural shape and flow. These actions are team”water viewapproach, which aims to strengthen the connection between a healthy river and the surrounding landscape by restoring the free flow of water and enhancing blue-green corridors for nature and wildlife. This September, the second year of the Abramson River restoration, the The team organized a helicopter airdrop to drop 150 tons of sand and gravel into the restored stretch of river.

Why do they do this? What impact does the team expect to have? We spoke to Vebjørn Kveberg Opsanger, a Norwegian PhD student based in Trondheim norwegian institute for nature research (NINA) Participate in monitoring and explain.

Why do sand and gravel fall into rivers?

In the early twentieth century, Abramson was heavily influenced by Sweden's industrial-scale forestry. To facilitate the transportation of logs, large boulders were removed from the riverbed and stacked along the riverside, and wooden floors made of individual tree trunks were laid in parts of the river. The river channels were also straightened and narrowed to further enhance the floating process of the wood.

This channelization increases the flow of water in the river, thereby washing away nearly all of the fine-grained sediment in small patches and backwaters that would naturally exist around larger stones in the river bed. Almost all was washed downstream. Without this sediment, many benthic insect larvae (or benthic fauna) would lose their habitat, so their numbers would decrease and disappear. In addition, fish spawning grounds and freshwater pearl oyster habitats have been lost.

Recent efforts by the Swedish Rewilding Team have reversed the channelization of the Abramson River and helped restore the water’s natural flow. But the fine-grained sediments are still missing, and it will take centuries for them to naturally build up again. By reintroducing sand and gravel, the aim is to accelerate the recovery of a range of benthic species, promote the reproduction of fish such as trout and salmon, and increase mussel populations.

Why are benthic insect larvae important to ecosystems?

Benthic fauna is a general term for small animals that live at the bottom of rivers and lakes and includes many different groups such as insect larvae, small bristleworms, nematodes, mussels, snails, clams, mites, beetles, and leeches. Allowing populations of these animals to recover in the Abramson River will help retain more nutrients in the restored stretch as they feed on organic matter in the water, such as from leaves. Predatory animals such as fish then feed on the benthic fauna. Therefore, there is potential for enhancement of the entire food web. Benthic animals also act as decomposers and help purify water through filtration.

How long will it take for the effects of decline on benthic fauna to become apparent?

Although there have been initiatives to return gravel to rivers in northern Sweden in the past, these have mainly targeted fish. This is the first intervention of its kind to primarily target benthic fauna, so it is difficult to say exactly how long it will take for the positive effects of sand and gravel falling to become apparent on this fauna, and how long that impact will occur. What will be.

As part of my PhD, I will be involved in monitoring this impact. I have been collecting samples in the Abramson River over the summer to measure benthic fauna before sand and gravel fall into the river. I haven't finished analyzing these samples yet, but expect the number of sand and gravel residents to be quite low compared to natural stretches of other rivers in the same area.

I will return to Abramson in 2025 and 2026 to see how benthic populations have changed. A remediation site with no added sand and gravel will serve as a control site. Dispersal from other rivers may take some time in terms of insects and other benthic animals recolonizing sediments. I hope we'll see some positive effects in two years and look forward to providing you with some updates.

Does the natural flow of the river contribute to the distribution of sand and gravel?

Yes, indeed. As far as fine sediment goes, nothing in the river is guaranteed to stay there. Helicopters spread sand and gravel at various locations in the Abramsen River section recently restored by a Swedish rewilding team. Much of this may have been redistributed by the natural flow of rivers, but some accumulates where it is found naturally. In fact, 150 tons sounds like a lot, but it's actually less than you might think, when the stones were placed in the river to fill the cavities and holes created in the river bed between and under the larger stones as part of the restoration process return.

If this intervention proves successful, the team will consider using the same approach in other stretches of the Abramson River, as well as stretches of other rivers where restoration will continue.

Funding for Abramson's sand and gravel return comes from EKO Energy Corporation.

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