Several hundred years before Europeans settled in North America, small Native American farming communities were already having a big impact on eastern flood plains — clearing the land and thus increasing erosion, runoff and flooding.

Gary Stinchcomb of Baylor University in Waco, Texas, and his colleagues dug deep into the banks of the Delaware River at a site in Pennsylvania looking for prehistoric changes in soil chemistry and sediment particle size, and for ancient plant material. They found increased sediment deposits from AD 1100–1600 — an indicator of elevated erosion — as well as signs that humans had cleared trees around rivers to farm corn. The erosion and flooding were made worse by the wet climate of the Little Ice Age in AD 1450–1530. European settlers later caused further ecological changes to the flood plains as a result of their various land-use practices.

Geology 39, 363–366 (2011)