Some of the major human influences on water quality, in particular the ways we use land, water, and chemicals, have undergone dramatic changes over the last five decades, according to a new study by the U.S. Geological Survey (USGS) National Water Quality Program. Patterns of urbanization, chemical use, and agricultural production are profoundly altered.
Some U.S. urban and agricultural areas and practices are almost unrecognizable from the way they were in the 1970s. From 1974 to 2012, urban areas increased by almost 70% (50 million acres), with the greatest growth in low-density “exurban” residential areas. Crop production increased 114% while cropland area increased only 23%, reflecting a vast growth in agricultural productivity. Animal production, particularly of hogs and pigs, became much more concentrated—the number of hog and pig farms decreased from a half million in 1974 to 63,000 by 2012, yet the number of hogs and pigs increased 45%.
The USGS study assessed a total of 61 human influences in 16 categories, including land use, agricultural practices, and population density. Some of the changes in those influences reflect regulatory actions. For example, from 1974 to 2012 there was a widespread and rapid increase in the use of the herbicide glyphosate with concurrent decreases in other herbicides resulting from their regulatory phaseout. Another example was the widespread decrease in atmospheric deposition of sulfate related in part to the Clean Air Act.
This publication provides comprehensive maps and summary statistics for the 61 human influences considered. Information on how major potential influences on water quality have changed over time provides a foundation for research to quantify the effects on water quality in U.S. rivers and streams.