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Brown water: low nitrate levels are problematic in some places
While it is well known that our waterworks are affected by regionally high nitrate values, a completely new problem has been emerging elsewhere for some time: too little nitrate. The decline in industrial emissions has almost brought some regions to pre-industrial levels in terms of nitrogen levels in the air and soil.
According to the Helmholtz Center for Environmental Research (UFZ), brown water is often reported as a problem in drinking water production, especially in catchment areas close to nature with lots of forest. Research has now shown that this is due to insufficient levels of reactive nitrogen in the atmosphere, thus in floodplain soils and inflows to the dams. Sometimes the nitrate levels here are below 6 mg / liter of water. So far below the limit of 50 mg, which is exceeded in some places due to excessive slurry inputs and also causes problems with water treatment.
But why isn't too little nitrate good? This is pure chemistry and the soil in the floodplain is the laboratory: free carbon, phosphate and some metals are bound to iron compounds in the soil. Low nitrate levels allow chemical reductions in these compounds, with the result that carbons, phosphate and some metals are washed out. They are partly responsible for the brown color and partly for increased algae growth. Neither is a concern for consumers, but the costs for drinking water treatment are increasing, the scientists say. The study, funded by the Federal Ministry of Education and Research, is now to be the basis for future experiments, from which concrete measures for problem solving are to be derived. Friederike Heidenhof, aid