Many people are curious about Iowa stream nitrate before modern agriculture became established across the landscape. They want to know what the “natural” level of nitrate was. It turns out we do have some actual data. In 1955, the Iowa Geological Survey published a document titled “Water-Supply Bulletin No. 5, Quality of Surface Waters of Iowa, 1886-1954” (1). Some of these data are shown below (as nitrogen).
Confluence of the … [more…]