A study found that climate change is affecting the quality of drinking water. The study was published in the journal “Water Research”.
Heat waves, droughts, floods, forest fires, the consequences of climate change are increasing and modifying our environment. A prime example is the countryside in the catchment area of the Rappbode reservoir in the eastern Harz region. It is the largest drinking water reservoir in Germany and supplies around one million people with drinking water. Long periods of drought in the years from 2015 to 2020 weakened the tree population in the Harz region so severely that pests such as bark beetles were able to spread. This further exacerbated the effect: the trees were further damaged and soon died. “Over the past four years, the Rappbode catchment, characterized by conifers, mainly spruces, has lost more than 50% of its forest,” says UFZ hydrologist and final author, Professor Michael Rode . “This massive forest dieback is progressing rapidly and is dramatic. This will have consequences for the drinking water reservoir.” Forests play a key role in the water cycle. They filter water and bind nutrients and are therefore necessary for good water quality. The fewer nutrients – i.e. nitrogen or phosphorous compounds – contained in the tank water, the better it is for drinking water treatment. “This makes it more difficult for algae to grow, which makes drinking water treatment in aqueducts more cost-effective and easier,” says UFZ Lake researcher and co-author Dr. Karsten Rinke. “Nutrient management in water conservation areas is therefore very important. In recent decades, long-term concepts with close cooperation between forest and water management have advanced the development large areas of forest in the catchment area of the Rappbode Reservoir.” The rapid decline of forests in the eastern Harz region is now a matter of serious concern for operators of reservoirs and aqueducts.
Stimulated by this development, the UFZ team investigated the effects of climate-induced deforestation on reservoir water quality in their model study. This study was based on data from the network of environmental observatories TERENO (Terrestrial Environment Observatories), in which the UFZ participates with the Observatory of the Harz/Central German Lowlands. “We were able to access environmental data over a period of more than ten years, which provided us with a solid data set,” says Dr. Xiangzhen Kong, also an environmental scientist at UFZ and lead author of the study. . The team used data from the international Inter-ectorial Impact Model Intercomparison Project (ISIMIP) to predict future climate change. “We first fed this data into a model to estimate climate-related effects on the nutrient balance in the watershed,” Kong says. “The resulting data was then processed into a reservoir ecosystem model with which we were able to determine the effects of different deforestation scenarios on predicted water quality for 2035. The Rappbode reservoir is fed by three catchments different, two of which have been included in “The Hassel catchment is characterized by agriculture, while that of the Rappbode is mainly forest – at least that was the case before the death of the spruce forests”, explains Kong. Before the water from the two catchments flows into the large Rappbode, it is first held back by a pre-dam upstream.The agricultural influence results in a significantly higher nutrient content in the water. of the Hassel pre-dam than in the Rappbode pre-dam.” We were able to demonstrate that, for a predicted deforestation of up to 80%, the Rappbode pre-dam will experience an 85% increase in dissolved phosphorus concentration and a more than 120% increase in itrogen concentration in just 15 years. The Rappbode pre-dam will thus achieve almost the same nutrient levels as the Hassel pre-dam,” says Kong. This will result in over 80% increase in diatoms and over 200% increase in green algae in the Rappbode pre-dam. These results highlight the future need for a wide range of adaptations in the management of drinking water. “Nutrient inputs to reservoir catchment areas should be reduced even more than before, reforestation projects with drought-resistant tree species should be further encouraged, and hydraulic works should be adapted to impending developments. with selective water removal strategies,” says Rode. “And what remains important and needs to be further increased: in-depth, granular environmental monitoring.”
The results for the Rappbode reservoir can be applied to other reservoir catchment areas in similar regions. “Forest dieback as an indirect consequence of climate change has a more pronounced effect on reservoir water quality than direct climate change effects such as rising water temperatures. been surprised by the magnitude of this effect,” Kong says. (ANI)
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