Anthropogenic impacts on mud and organic carbon cycling

Abstract

Fine-grained muds produced largely from rock weathering at the Earth’s surface have great influence on global carbon cycling. Mud binds and protects organic carbon (OC) from remineralization, and its organic loading controls the amounts, timescales and pathways of OC sequestration in sediments and soils. Human activities have resulted in marked changes (both increases and decreases) in mud accumulation and associated OC (mud–OC) loadings in different environments via altering organic matter inputs and reactivity. Such impacts on mud and mud–OC can be directly caused by activities such as damming and levee building, or indirectly result from human-induced climate change. Here we present a synthesis of impacts of human activities on the production, transfer and storage of mud–OC. In general, we find that anthropogenic climate warming has increased net fluxes of mud–OC in most of the systems discussed here (for example, mountain glaciers, land erosion, dam burial, river export, permafrost thaw, ice-sheet erosion and burial in margins), with uncertainties for tidal flats and floodplains, and probably net losses for coastal wetlands. Whether the anthropogenic mobilization of mud–OC results in more or less sequestration of OC is not known with the current data, as it is dependent on timescales that involve complex transient effects. Human activities have altered the production, transport and fate of mud and associated organic carbon, with important implications for global carbon cycling.