A 7000-year record of human influence on Global River Deltas: Geomorphology, stratigraphy, the Anthropocene overprint and future

Abstract

With the inception of most of the world's deltas about 8000 years ago, deltaic floodplains started offering, about a thousand years later, arable land, water and ecosystem services for early human settlements. We identify delta geomorphic changes and proxies and geoarchaeological markers of the human presence on deltas and in their stratigraphy over the last 7000 years, and from ancient maps. We analyse the human-delta relationship in four phases: Neolithic, Metal Ages, Common Era, and Anthropocene, marking increasing human adaptation to changing delta geomorphology modulated by fluctuations in relative sea level and fluvial sediment supply. These adaptations fostered the emergence of urbanization and served as a catalyst for technological innovation and human modification of deltas. The sparse Neolithic human presence in delta stratigraphy gradually expanded to become pervasive in the contemporary Anthropocene, reflecting the twin effects of global population growth and increasingly favourable conditions for humans. We explore the links between early deltaic and non-deltaic communities and gauge the impact of humans on sediment supply from river catchments, and its consequences, notably in terms of frequent delta avulsions, expansion or vulnerability, and explore its inextricable links with climate variation. The Anthropocene is witnessing a profoundly transformed, globally distributed, human-managed delta landscape dominated by important urbanization, reduction in sediment supply, increasing intentional but also unintentional delta modifications, and vulnerability to sea-level rise compounded by exacerbated subsidence. Understanding the human-delta relationship over the past 7000 years contributes to fostering stronger links between geoscience and cultural heritage, to better delta management and sustainability, including an upstream river-basin scale perspective, and to better anticipation of delta futures, notably under the threat of sea-level rise.