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United States Department of Agriculture

Agricultural Research Service

Title: Problems Associated with Comparing in Situ Water Quality Measurements to Pollution Model Output for Geographical Analyses

Authors
item Finn, M - USGS
item Bosch, David
item Usery, E - UGA
item Hartman, A - USGS

Submitted to: Association of American Geographers
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2006
Publication Date: March 7, 2006
Citation: Finn, M.P., Bosch, D.D., Usery, E.L., Hartman, A.G. 2006. Problems associated with comparing in situ water quality measurements to pollution model output for geographical analyses [abstract]. Association of American Geographers. March 7-11, 2006, Chicago, IL.

Technical Abstract: We are using data to quantify and assess the significance of sediment, nitrogen, phosphorus and other nutrient output from the Agricultural Non-Point Source (AGNPS) pollution model in relationship to hydrologic field data from the Little River watershed in Georgia. In an effort to quantify the effects of resolution on model results, we attempt to establish measures of accuracy for each of the 51 output values relative to a corresponding in situ water quality measurement. Efforts to quantify the significance of input spatial resolution on the physical, chemical, and hydrologic model output values are problematic due to convoluted matching of these values to the collected in situ measurements. Curves representing the accuracy of the results were created using mathematical means such as cubic splines and logistic regression. We intend to quantify a spatial resolution threshold by examining this curve through which any increasing resolution does not provide any increasing accuracy of the model output. Obstacles to achieving this are the difficulty of assembling the in situ data from wide and disparate sets of data sources such as information in published literature and on websites, files on archived media, and tables in documents. Out of 51 output parameters, we have matched only 2 measured parameters directly and an additional 6 values indirectly. Overcoming these problems and quantifying this spatial threshold relative to AGNPS will provide insight to the contribution of geospatial resolution to the variance of output values from AGNPS and, thus, insight on the analyses of water quality investigations.

Last Modified: 10/30/2014
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