What was done
The author determined how the conversion of the Upper Mississippi River Valley from prairie and forest to crop and pasture land by settlers in the early 1800s influenced subsequent watershed runoff and soil erosion rates.

What was learned
It was learned that conversion of the region's natural landscape to primarily agricultural uses boosted surface erosion rates to values three to eight times greater than those characteristic of pre-settlement conditions.  In addition, the land use conversion increased peak discharges from high-frequency floods by 200 to 400%.  Since the late 1930s, however, surface runoff has been decreasing; but this decrease "is not associated with climatic causes," according to the author, who reports that "an analysis of temporal variation in storm magnitudes for the same period showed no statistically significant trend."  Other notable findings include the observation that since the 1940s and early 1950s, the magnitudes of the largest daily flows have been decreasing at the same time that the magnitude of the average daily baseflow has been increasing, indicating a trend toward fewer flood and drought conditions.

What it means
It is important to note that the decreases in soil erosion rates and extreme streamflow conditions beginning in the late 1930s in the Upper Mississippi River Valley are completely opposite from climate alarmist and model predictions, which suggest these parameters should be increasing as a result of unprecedented CO2-induced global warming.  However, they likely are not related to things climatic, as the author attributes them to the introduction of soil conservation measures, such as contour plowing, strip-cropping, terracing and minimum tillage.

There is likely another important factor that is also involved.  As we have indicated in several Journal Reviews and Editorials (see Long-Term Effects of Elevated Atmospheric CO2 on Soil Fungi, Rising Atmospheric CO2 Concentrations Reduce Soil Erosion: Lessons for the New Millennium, Effects of Elevated CO2 on Soil Microbiota, and The Long, Long Reach of Atmospheric CO2 Enrichment), the concomitant rise in atmospheric CO2 concentration and its aerial fertilization effect, which enhances plant growth that helps to stabilize soil both on the surface and belowground, has probably played a significant role as well.