Acid rain seems to be a thing of the past, yet sulfate continues to rise in many inland waters worldwide. Researchers led by the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) and the Danish University of Aarhus provide an overview of the sources of sulfate and its effects on freshwater ecosystems. They point out that the negative consequences for ecosystems and drinking water production have so far only been perceived regionally and recommend that sulfate be given greater consideration in legal environmental standards.
When fossil fuels are burned, large amounts of sulfur are oxidized and released into the atmosphere. In North America and Europe, after power plants were retrofitted with flue gas desulphurisation in the 1980s, atmospheric sulfur inputs decreased significantly—in Germany by 90 percent in the last thirty years. The danger of "acid rain" seemed to have been banished. Nevertheless, sulfate concentrations in inland waters have hardly decreased or even increased in many regions of the world in recent decades. For the researchers, this is a clear sign that other pollution sources have gained in importance.
Drainage, opencast lignite mining and artificial fertilizers are among the main causes
Dissolved sulfate is naturally formed in inland waters by mineral weathering, volcanism or the decomposition and combustion of organic matter. Human activities increase the concentrations of sulfate in water. In addition to atmospheric inputs, the drainage of wetlands, the lowering of groundwater levels for opencast lignite mining, fertilizer leaching from agricultural soils and agricultural and industrial wastewater are primarily responsible for this.
Fertilizers and pesticides surpass acid rain in man-made sulfur input
The researchers also refer to a recent study by the American University of Colorado on a previously underestimated source of sulfur—agriculture. Sulfur-containing substances are used as fertilizers, but also as fungicides, for example in viticulture. Worldwide, agricultural use accounts for about 50 percent of the sulfur discharged into the environment each year, according to the US-study. In some areas of agriculture and thus also in some regions of the world, more sulfur is now entering soils and waters than at the peak of acid rain.
Climate change exacerbates the situation
Several climate change factors are expected to lead to a significant increase in sulfate concentrations in water bodies. "Increasing heavy rainfall washes sulfurous soils and fertilizers into water bodies; larger areas of wetlands fall dry; rising sea levels increase the amount of sulfate-rich saltwater entering groundwater and rivers, which can significantly increase sulfate concentrations," says Dr. Dominik Zak from the Danish University of Aarhus, summarizing the projections he and his co-authors have compiled in the overview study.