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More moor, please

The retention of water in the landscape is a major challenge for agriculture and nature conservation in times of climate change. The restoration of formerly drained wetlands and the re-colonization by beavers along a river network have an influence on the water balance of the landscape. Doerthe Tetzlaff’s team has investigated the long-term effects of these two factors on the water regime and water quality of watercourses in the agricultural region in a tributary of the River Spree in the north-eastern lowlands of Germany using extensive data from the last 30 years.

The beaver has returned to Brandenburg. Dörthe Tetzlaff's team investigated its influence on the water balance. Photo: shutterstock

The researchers were able to show that restoration measures and the re-colonisation of the beaver along the investigated river network have led to an increase in the groundwater level since 2000. In the region, about 90 percent of the total precipitation is returned to the atmosphere by evapotranspiration from plants and soils. Before 2010, less than 5 percent of the precipitation recharged into groundwater. This has increased with restored wetland and the re-colonization by beavers although, the proportion of rainfall recharging groundwater remains below 10 percent. Wetland restoration, greatly enhanced by increasing beaver populations, resulted in longer water transit times in the stream network, less linear storage-discharge relationships and a loss of daily stream variability. However, rising groundwater levels had to date had less of an impact on stream flow than expected.

“The proportion of rewetted moorland areas compared to agricultural land is probably still too low to significantly affect the discharge of water in the landscape”. In addition, Aaron Smith, IGB researcher and lead author of the study, also emphasises that in this study several small, rather than larger, contiguous moor areas were rewetted. The researcher recommends wetting more former moorland areas, but in larger, connected portions. This could improve the retention of water in agricultural landscapes.

In addition, there was surprisingly limited long-term water quality improvements from the wetland Rehabilitation. "This probably reflects the long-term legacy of fertiliser use on nutrient reserves in soils, groundwater and waters in this catchment area. It shows that changes in land use and restoration measures often take several decades to take effect", says Dörthe Tetzlaff.

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