Assessment of Environmental and Management Factors Impacting the Phosphorus Loading in an Agricultural Watershed
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Runoff with high phosphorus (P) concentrations from agricultural, industrial and domestic land uses is contributing to detrimental environmental changes throughout the entire ecosystem. To examine this phenomenon, three studies examining P were conducted. The first study was devoted to water and P budgets of a large agricultural basin located in South Florida (Everglades Agricultural Area, EAA). Water and P budgets were computed from 2005 to 2012. The annual surface outflow P loading from the EAA averaged 157.2 mtons originating from Lake Okeechobee (16.4 mtons, 10.4%), farms (131.0 mtons, 83.4%), and surrounding basins (9.8 mtons, 6.2%) after attenuation. Farms, urban areas, and the adjacent basin contributed 186.1, 15.6, and 3.8 mtons/yr to the canals, respectively. The average annual soil P retention was estimated at 412.5 mtons. Moreover, results indicated that the canals acted as a P sink storing 64.8 mtons/yr. To assess the P loading impact of farm drainage on the canals and on the outflow, dimensionless impact factors were developed. The second study developed a new methodology using multi-temporal Normalized Difference Vegetation Index (NDVI) data derived from Landsat images to map sugarcane and its rotation in the EAA. A cloud and cloud shadow removal procedure that applies to patchy clouds over agricultural fields was developed to facilitate crop mapping. Three classes related to sugarcane planting and crop rotation (sugarcane, mixed crops, and fallow) were generated using a Decision Tree Analysis (DTA) algorithm. The DTA model can produce up-to-date agricultural maps for the purposes of environmental management and therefore circumvents issues related to limited field data. The third study combined the results of the first two studies to identify environmental and management controls of P loading in the EAA from 2010 to 2014. Multivariate analyses were conducted using the following environmental variables for 38 farms in the S5A sub-basin: (1) total P load per unit area (2) best management practices (BMP) types (3) land cover (4) soil type (5) current and antecedent rainfall (6) distance of farms from sub-basin outlet (7) farm perimeter and (8) seasonality. Current and antecedent rainfall contributed significantly to the release of P load in the farm runoff. P load was also influenced by the percentage of mixed vegetation land cover, the interaction of seasonality and BMP type, farm perimeter and distance of farms from sub-basin outlet.
Farid Marandi, Sayena (2017). Assessment of Environmental and Management Factors Impacting the Phosphorus Loading in an Agricultural Watershed. Doctoral dissertation, Texas A & M University. Available electronically from