THE CAUSES AND CONSEQUENCES OF EARLY AGRICULTURE AND FLUVIAL ACTIVITY THROUGHOUT EASTERN NORTH AMERICA

Understanding the associations and long-term relationships between agriculture, climate and hydrology is critical for modeling the future demands of an agriculturally-based civilization. This study explores links between the emergence and evolution of agriculture and fluvial history throughout eastern North America (ENA) using radiocarbon meta-analysis. We compiled 354 previously reported radiocarbon ages for the Holocene (11.7 ka – 0 ka), which were classed into one of three fluvial stratigraphic contexts: buried soil, alluvium, basal-channel alluvium. Normalized cumulative probability density curves were generated using CALIB 5.0.1 for the three stratigraphic contexts. The results show three distinct intervals of high fluvial activity and low floodplain stability: 11.7 –10.3ka, 7.4–5.5ka, and 1.0–0ka. The late Pleistocene-early Holocene (11.7-10.3ka) interval coincides with a waning Laurentide ice sheet and rapid climate change events. The middle Holocene (7.4-5.5ka) interval of fluvial activity is followed by a general increase in basal-channel alluvium activity (5.5-3.5ka), suggesting that many low-lying channels are beginning to fill in during this time. This mid-Holocene period of fluvial activity coincides with an increased human presence in riverine environments as well as a heightened reliance on weedy floodplain annuals. While climate change likely drove the change in fluvial style circa 5.5ka, the combined human-hydrological-ecological dynamic ultimately influenced plant domestication in ENA circa 4.5ka. The late Holocene (1.0-0ka) rise in fluvial activity is likely the combined effects of prehistoric maize farming and Colonial-era thru modern farming and stream engineering. Although middle-Holocene climate and fluvial style change appears to have partly driven the plant domestication in eastern North America, late Holocene fluvial activity appears to be the consequence of intensifying maize-based agriculture and rise of complex civilization (e.g. Mississippian, Iroquoian).