Holocene and Anthropocene Landscape Change

In this study, we untangle the relative importance of climatic, tectonic, and anthropogenic drivers as triggers of arroyo formation and geomorphic change for a small watershed on Santa Cruz Island, California. Within the Pozo watershed (6.47 km2), historic arroyo incision occurred contemporaneously with arroyo incision across many of the world's dryland regions. Unlike many of these other sites, Pozo contains a datable record that allows quantification of sedimentation rates from the mid-to-late Holocene to the twentieth century. Basin-wide environmental changes were assessed using a combination of cosmogenic radionuclide inventories, midden and marine-shell deposits, relict soil properties, airborne and ground-based light detection and ranging (lidar) data, ranching artifacts, and historic records. Shortly after the introduction of sheep in 1853, localized sedimentation rates on the Pozo floodplain increased by two orders of magnitude from 0.4 mm/year to ∼25 mm/year. Accelerated sedimentation was followed by arroyo formation ca. 1878 and rapid expansion of the incipient gully network, the lateral extent of which has been largely maintained since 1929. Catchment-mean erosion rates from cosmogenic radionuclide measurements indicate that presettlement rates were less than 0.08 mm/year, whereas lidar-derived measurements of historic gully erosion produce estimates almost thirty times higher (∼2.2 mm/year). Topographic measurements since 2005 indicate that the active channel of the Pozo watershed is aggrading. We argue that accelerated sedimentation due to overgrazing, and an unusually large 1878 rainstorm event, set the stage for arroyo formation in the Pozo watershed between 1875 and 1886. We hypothesize that even in the absence of modern human disturbance, downcutting would have occurred due to intrinsic hillslope stability thresholds

Alluvium · Cartography · Colluvium · Cosmogenic nuclide · Drainage basin · Erosion · Fluvial · Geography · Geomorphology · Holocene · Hydrology (agriculture) · Midden · Palaeochannel · Physical geography · Radiocarbon dating · Sediment · Sedimentation · Structural basin · Tephra · Volcano · Watershed · Geology · Geology and Paleoclimatology Research · Hydrology and Sediment Transport Processes · Paleontology · Soil erosion and sediment transport

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  Open Access•Katharine M Johnson, William B Ouimet•Anthropocene•2016

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• Anthropocene Landscape Change and the Legacy of Nineteenth- and Twentieth-Century Mining in the Fourmile Catchment, Colorado Front Range

  David P Dethier, William B Ouimet et al.•Annals of the American…•2018

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• Ephemeral-Stream Processes

  Open Access•Peter C Patton, Stanley A Schumm•Quaternary Research•1981

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• Holocene Paleoecology of an Estuary on Santa Rosa Island, California

  Open Access•Kenneth L Cole, Geng-Wu Liu et al.•Quaternary Research•1994

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• Dirt

  David R Montgomery•Dirt•2007

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• A 17,000-year glacio-eustatic sea level record

  Open Access•Richard G Fairbanks•Nature•1989

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• Soil erosion and the global carbon budget

  Open Access•Rattan Lal•Environment International•2003

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• Calibration of the 14C timescale over the past 30,000 years using mass spectrometric U–Th ages from Barbados corals

  Open Access•Edouard Bard, Bruno Hamelin et al.•Nature•1990

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• The Island Chumash

  D J Kennett•Island Chumash•2005

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• Sedimentation and soil formation phases in the Ghardimaou Basin (northern Tunisia) during the Holocene

  Open Access•Christoph Zielhofer, Dominik Faust et al.•Quaternary International•2002

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• Discussion Reporting of 14 C Data

  Open Access•Minze Stuiver, Henry A Polach•Radiocarbon•1977

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• Valley Alluviation in Southwestern Wisconsin∗

  James C Knox•Annals of the Association of…•1972

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• Human Impacts on Wisconsin Stream Channels∗

  James C Knox•Annals of the Association of…•1977

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• Historical Valley Floor Sedimentation in the Upper Mississippi Valley

  James C Knox•Annals of the Association of…•1987

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• The Arlington Spring Site, Santa Rosa Island, California

  Open Access•Phil C Orr•American Antiquity•1962

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