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Human Amplified Natural Change: An approach for vulnerability assessment and mitigation planning
American Geophysical Union, Fall Meeting 2011 (2011)
  • Patrick Belmont, Utah State University
  • P Wilcock
  • K B Gran
Addressing the environmental impacts of agricultural development is made difficult by the scale and complexity of the natural system, the pervasive human alteration of that system, the contingent and nonlinear nature of system response, and the web of natural-human interactions driving social, economic, and regulatory decisions over periods of decades to centuries. One of the most difficult challenges is determining those locations within the landscape that are most sensitive to change. One approach is the concept of human-amplified natural change (HANC), a hypothesis that states that areas of the landscape that are most susceptible to human, climatic, and other external changes are those that are undergoing the highest rates of natural change. High variability in system response implies that there are locations and moments that are especially vulnerable to changes in climate and human actions. These 'critical areas' are not only essential to understand for mitigation purposes, but also serve as targeted locations in which to monitor change in an accelerated environment. Under the HANC hypothesis, it is these locations that should be the focus for both research and management. We explore the HANC hypothesis using the case of sediment delivery to the Upper Mississippi River. Work on Lake Pepin, a natural lake on the Mississippi River, has shown that sediment supply has increased ten-fold over the past 150 years. This period corresponds with widespread implementation of drainage and row cropping in the Minnesota River Basin, the primary contributor of sediment to the Upper Mississippi. Although this development is clearly important, the watershed was geologically primed to produce large amounts of sediment as it incises through soft glacial sediments in response to a base level fall associated with the carving of the Minnesota River valley over 13,000 years before present. The nearly complete transformation of the land surface, vegetation, and hydrology over the past two centuries has increased already large sediment loadings by a factor of four to five. A combination of geochemical fingerprinting and a sediment mass balance for a major subwatershed of the Minnesota have demonstrated that, although the sediment loading remains very large, the dominant source of sediment has shifted from agricultural fields to accelerated erosion of stream banks and bluffs. The likely cause of these elevated erosion rates is increased river flow, which results from both changing precipitation patterns and pervasive changes to upland hydrology. Because of the geologic history and setting, these near-channel areas are vulnerable to accelerated erosion, and hydrologic changes in the upper watershed have had large impacts on sediment loading.
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Patrick Belmont, P Wilcock and K B Gran. "Human Amplified Natural Change: An approach for vulnerability assessment and mitigation planning" American Geophysical Union, Fall Meeting 2011 (2011)
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