Naturbaserte løsninger med fokus på restaurering og miljødesign i elver

Freshwater ecosystems are among the most threatened ecosystems worldwide, and freshwater species globally have experienced population declines, with many becoming extinct. Population declines and extinctions of freshwater species can be linked to the development and operation of hydropower, pollution, fertilizer runoff from agriculture, and habitat destruction due to industry, urbanization, and infrastructure. In a review of restoration in Norwegian rivers, hydropower, acid rain, flood control measures, and infrastructure development such as roads have been identified as the major impacts. Measures such as liming, which addresses acid rain, have shown great success. Large amounts of lime are dumped into the river to counteract the effects of acid rain, and as long as the supply of lime continues, salmon and acid-sensitive species have returned to the rivers. Measures aimed at rivers used for hydropower production have had more mixed success, likely because the problem that needs to be addressed to restore the river’s ecosystem—the hydropower plant—cannot be removed. Salmon and trout are the species that receive the most attention in most restoration projects, while other aquatic organisms like water algae, aquatic plants, Arctic char, aquatic insects, and freshwater mussels have few or no dedicated restoration projects. Projects aimed at improving conditions and increasing the production of salmon and trout often involve altering the physical environment of the river. This may include placing large stones and dead wood in the river, restoring the river’s course to a more natural form, and removing fine sediments that clog fish hiding spots. In a case study in the river Eira, the effect of a type of measure called "ripping" is being examined. Ripping is a method used to remove fine sediments, such as sand, from the riverbed. In many rivers where water has been diverted for hydropower production, the river does not experience large enough floods to wash out fine sediments. The natural riverbed, which mainly consists of gravel and stones, becomes buried in sand. The sand clogs all the cavities in the riverbed that juvenile fish use for hiding, contributing to lower survival rates of salmon and trout before they start their migration to the sea. By using long-term data on juvenile fish densities from NINA, this study will examine the effects of ripping. Ripping as a method can cause significant disturbances for organisms living in the affected areas, as excavators are used to tear up and lift the substrate from the riverbed to dislodge the fine sediments from the stones and gravel. This can have short-term negative effects on bottom-dwelling organisms. Beyond the disturbance caused by the work itself, it may also have a positive effect, as many species and groups of bottom-dwelling organisms prefer to live in the cavities between stones. There is little knowledge about the effects of ripping on bottom-dwelling organisms. Where the river Eira struggles with too much sand, there are signs that the river Abramsån in Swedish Lapland has too little sand. A hundred years ago, Abramsån was degraded by loggers to make it better for transporting timber. All the large stones in the fast-flowing sections were removed, and at the same time, these sections were also channelized. To rectify past mistakes, the Rewilding Sweden foundation started a restoration project in Abramsån in 2023 with the goal of returning the river to a natural state. Stones were placed back, and the riverbed was widened again, but a hundred years of channelization had washed away all the sand from the riverbed. Channelization increases the water speed in the river, which boosts the transport of sand, gravel, and stones through the watercourse. The lack of large stones also meant that the small pockets of slower-flowing water created by the large stones disappeared, so the sand could no longer be trapped and remained on the riverbed. Unlike many Norwegian rivers, there is little erosion of sand and other fine sediments in Abramsån, and it has been estimated that it will take 1,000 years for the river to regain its natural amount of sand. Many bottom-dwelling organisms like the cavities between and under stones but also spend most of their lives buried in sand and gravel. There were plenty of cavities in Abramsån, but little sand to be seen on large parts of the riverbed. To try to recreate natural patches of sand within this millennium, Rewilding Sweden decided to expedite the process by dumping 120 tons of sand and fine gravel along a section of the river. Before this dumping occurred, quantitative samples of bottom-dwelling organisms were taken before the sand was dumped in 2024. When new samples are taken in 2025, it will be possible to see if this sand dumping has managed to increase the number of species of bottom-dwelling organisms in the river, and whether any species or groups of organisms may have been harmed by the sand dumping