The impact of humans on continental erosion and sedimentation

Abstract

Research Article| January 01, 2007 The impact of humans on continental erosion and sedimentation Bruce H. Wilkinson; Bruce H. Wilkinson 1Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA Search for other works by this author on: GSW Google Scholar Brandon J. McElroy Brandon J. McElroy 2Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Bruce H. Wilkinson 1Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA Brandon J. McElroy 2Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Publisher: Geological Society of America Received: 19 Sep 2005 Revision Received: 12 May 2006 Accepted: 05 Jul 2006 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 GEOLOGICAL SOCIETY OF AMERICA GSA Bulletin (2007) 119 (1-2): 140–156. https://doi.org/10.1130/B25899.1 Article history Received: 19 Sep 2005 Revision Received: 12 May 2006 Accepted: 05 Jul 2006 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bruce H. Wilkinson, Brandon J. McElroy; The impact of humans on continental erosion and sedimentation. GSA Bulletin 2007;; 119 (1-2): 140–156. doi: https://doi.org/10.1130/B25899.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Rock uplift and erosional denudation of orogenic belts have long been the most important geologic processes that serve to shape continental surfaces, but the rate of geomorphic change resulting from these natural phenomena has now been outstripped by human activities associated with agriculture, construction, and mining. Although humans are now the most important geomorphic agent on the planet's surface, natural and anthropogenic processes serve to modify quite different parts of Earth's landscape. In order to better understand the impact of humans on continental erosion, we have examined both long-term and short-term data on rates of sediment transfer in response to glacio-fluvial and anthropogenic processes.Phanerozoic rates of subaerial denudation inferred from preserved volumes of sedimentary rock require a mean continental erosion rate on the order of 16 m per million years (m/m.y.), resulting in the accumulation of ∼5 gigatons of sediment per year (Gt/yr). Erosion irregularly increased over the ∼542 m.y. span of Phanerozoic time to a Pliocene value of 53 m/m.y. (16 Gt/yr). Current estimates of large river sediment loads are similar to this late Neogene value, and require net denudation of ice-free land surfaces at a rate of ∼62 m/m.y. (∼21 Gt/yr). Consideration of the variation in large river sediment loads and the geomorphology of respective river basin catchments suggests that natural erosion is primarily confined to drainage headwaters; ∼83% of the global river sediment flux is derived from the highest 10% of Earth's surface.Subaerial erosion as a result of human activity, primarily through agricultural practices, has resulted in a sharp increase in net rates of continental denudation; although less well constrained than estimates based on surviving rock volumes or current river loads, available data suggest that present farmland denudation is proceeding at a rate of ∼600 m/m.y. (∼75 Gt/yr), and is largely confined to the lower elevations of Earth's land surface, primarily along passive continental margins; ∼83% of cropland erosion occurs over the lower 65% of Earth's surface.The conspicuous disparity between natural sediment fluxes suggested by data on rock volumes and river loads (∼21 Gt/yr) and anthropogenic fluxes inferred from measured and modeled cropland soil losses (75 Gt/yr) is readily resolved by data on thicknesses and ages of alluvial sediment that has been deposited immediately downslope from eroding croplands over the history of human agriculture. Accumulation of postsettlement alluvium on higher-order tributary channels and floodplains (mean rate ∼12,600 m/m.y.) is the most important geomorphic process in terms of the erosion and deposition of sediment that is currently shaping the landscape of Earth. It far exceeds even the impact of Pleistocene continental glaciers or the current impact of alpine erosion by glacial and/or fluvial processes. Conversely, available data suggest that since 1961, global cropland area has increased by ∼11%, while the global population has approximately doubled. The net effect of both changes is that per capita cropland area has decreased by ∼44% over this same time interval; ∼1% per year. This is ∼25 times the rate of soil area loss anticipated from human denudation of cropl