Floodplain and Terrace Legacy Sediment as a Widespread Record of Anthropogenic Geomorphic Change

Anthropogenic erosion and sedimentation are critical components of global change that involve life-sustaining natural resources of soil and water. Many geomorphic systems have responded to intense land use disturbance with episodic erosion and sedimentation, often orders of magnitude greater than background geological rates in the Holocene. Accelerated sedimentation is a metric for land use change and provides evidence of geomorphic change in fans, floodplains, terraces, deltas, lakes, karst sinks, estuaries, and coastal marine deposits. This review describes high variability in the timing of alluvial sedimentation and the value of bottomland stratigraphy with emphasis on records and heterogeneity of anthropogenic change. Although floodplain sedimentary evidence might be ill-suited for defining the proposed Anthropocene epoch boundary based on stratigraphic boundary criteria, sedimentology and stratigraphy provide rich evidence for long-term human activities that measures buildups of human environmental alterations long before the proposed mid-twentieth-century onset of the Anthropocene. Anthropogenic sedimentation is globally widespread but is too time-transgressive to serve as a stratigraphic indicator for onset of the proposed Anthropocene epoch. The emphasis here is on an example of longue durée; that is, the long record of anthropogenically accelerated sedimentation and the valuable evidence that it provides of human-induced environmental change. A conceptual tripartite model summarizes the evolution of anthropogeomorphic change. Anthropogenic sediments preserve geoarchaeological evidence and other important contextual information in buried landscapes that include human infrastructure, fields, material culture, contaminants, and paleosols. Geomorphic change can threaten food production, flooding, water quality, and so on. Understanding erosion and sedimentation dynamics is a vital concern for humanity.