According to a U.S. Geological Survey report published today in the Journal of Environmental Quality, drought periods followed by rainfall caused nitrate levels to increase to the highest ever measured in some Midwest streams during a 2013. “The highest nitrate concentrations in 2013 were in streams in Iowa, closely followed by southern Minnesota and central Illinois,” said Peter Van Metre, a USGS hydrologist and the lead author of the study. “Drought conditions in 2012 allowed excess nitrogen to build up in the soils until spring rains in 2013 flushed the nitrate into streams, leading to unusually high levels.” SILT is [...]