Humans impact Earth in many different ways. One of the most visually dramatic impacts is erosion caused by deforestation and intensive agriculture -- but does such erosion really matter?
To answer that question, Reusser and colleagues used exquisitely sensitive analyses to measure how quickly Earth's surface changes in the absence of humans. The team estimated natural rates of erosion by collecting sand from rivers draining the southeastern United States and measuring a rare isotope of beryllium produced near Earth's surface.
Their measurements show that before the arrival of Europeans, erosion was slow -- only a fraction of an inch every thousand years. Then, the settlers came, cleared the land, and erosion increased more than 100-fold. These measurements clearly demonstrate the dramatic effects that humans can have on the landscape.
So much soil sluiced off hillslopes that the rivers could move less than 10% of what was eroded. The rest was left behind on valley bottoms.
Background erosion rates are critical for developing realistic landscape management strategies. For example, the technique used in this study can determine whether rates of soil loss are sustainable and help regulators make decisions about allowable levels of sediment pollution in rivers.
Citation: Quantifying human impacts on rates of erosion and sediment transport at a landscape scale, Lucas Reusser et al., Geology http://dx.doi.org/10.1130/G36272.1