Dissolved organic carbon…………………………………………………………………2 1.2 Importance of dissolved organic carbon (DOC)………………………………………….6 1.3 Dissolved organic carbon and watershed land use……………………………………….9 1.4 Subsurface drainage and dissolved organic carbon……………………………………...16 1.5 Crop rotation, nitrogen fertilization, and dissolved organic carbon……………………..17 1.6 Influence of precipitation and irrigation on dissolved organic carbon…………………..18 1.7 Native perennial vegetation strips……………………………………………………….21 1.8 Objectives………………………………………………………………………………..26 CHAPTER 2: MATERIALS AND METHODS…………………...………………………..27 2.0 Site description and management………………………………………………………..27 2.1 Sample collection and analysis…………………………………………………………..28 2.2 Precipitation……………………………………………………………………………...29 2.3 Statistics………………………………………………………………………………….30 2.4 Hypotheses…………………………………………………………………...…………..31 iii CHAPTER 3: RESULTS………………………...…………………………………………..35 3.0 Precipitation……………………………………………………………………………...35 3.1 Flow weighted DOC concentrations…………………………………………………….36 3.2 Total DOC load exported………………………………………………………………..37 3.3 100% NPV watersheds…………………………………………………………………..40 CHAPTER 4: DISCUSSION………………………………………………………………...43 4.1.0 Hypothesis 1……………………………………………………………………………43 4.1.1 Treatment effects on DOC concentrations for the study period (2008-2010)…………43 4.1.2 Annual treatment effects on DOC concentrations……………………………………..44 4.1.3 Seasonal and monthly treatment effects on DOC concentrations……………………...46 4.1.4 Treatment effects during an extreme storm event August 8-11, 2010………………....48 4.1.5 Comparison of DOC concentrations between 100% NPV and treatment watersheds in 2010…………………………………………………………………………………49 4.1.6 Comparison of DOC concentrations between 100% NPV and treatment watersheds during August 8-11, 2010 storm event………………………………………………...50 4.2.0 Hypothesis 2……………………………………………………………………………51 4.2.1 Treatment effects on DOC loads for the study period (2008-2010)…………………...51 4.2.2 Annual treatment effects on DOC loads……………………………………………….52 4.2.3 Seasonal and monthly treatment effects on DOC loads…………………………….….56 4.2.4 Treatment effects during an extreme storm event August 8-11, 2010…………………57 4.2.5 Comparison of DOC load between 100% NPV and treatment watersheds in 2010…...58 4.2.6 Comparison of DOC load between 100% NPV and treatment watersheds during iv August 8-11, 2010 storm event………………………………………………………...59 4.3.0 Factors highlighting the need for future research……………………………………...60
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