Geology

Records in the River

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Science  01 Apr 2011:
Vol. 332, Issue 6025, pp. 15
DOI: 10.1126/science.332.6025.15-b

The expansion of agriculture, mills, and deforestation after colonial settlement of eastern North America expanded erosion and greatly affected the hydrology of streams and rivers. However, Native Americans had been practicing agriculture and forest management for several centuries before that. Stinchcomb et al. show that river hydrology was modified by, and so records, this history as well. They focused on the Delaware River Valley, where artifacts show widespread settlement from about 1100 to 1600 CE, including expansion of maize agriculture and forest clearing. Carbon isotope, radiocarbon dating, and phytolith analyses document the increase in maize and other grasses. Analysis of sediments shows increased sedimentation during this interval in stream valleys and also an increase in flooding. Together, the data imply that perhaps half of the surrounding forests were cleared in the local floodplain. Flooding may have been further augmented by cooler and wetter conditions from 1450 to 1530 CE. Thus, pre-Columbian agriculture and deforestation also left a marked sedimentary record, at least locally in North America.

Geology 39, 363 (2011).

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