Date of Award

5-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Agricultural and Biological Engineering

First Advisor

Bernard A. Engel

Second Advisor

Dennis C. Flanagan

Committee Chair

Bernard A. Engel

Committee Co-Chair

Dennis C. Flanagan

Committee Member 1

Keith Cherkauer

Committee Member 2

Venkatesh Merwade

Abstract

Analysis of the effects of implementing different conservation practices, as well as increased levels of conservation practices under existing and projected future climate, will determine if current conservation practice recommendations will be sufficient to maintain soil and water resources. The Soil and Water Assessment Tool (SWAT) was used to study four watersheds of different sizes (CCW = 680 km2, F34 = 183 km2, AXL = 42 km 2 and ALG = 20 km2) located in Northeastern Indiana. The overarching goal of this study was to evaluate the effect of various agricultural practices on runoff and agricultural chemical losses under current and future climate conditions, using an appropriately calibrated SWAT model.

The results indicated calibrating SWAT at one watershed size and applying the optimized parameters to watersheds of different sizes with similar physiographic features produced satisfactory predictions of streamflow, nitrogen and phosphorus losses. Between the baseline period (1961-90) and the end of this century (2099), average annual precipitation for the watershed is expected to increase by approximately 8.5%, average daily solar radiation will increase by approximately 2.4% and average annual maximum and minimum temperatures will increase by approximately 3.9 and 4.0° C respectively. Based on SWAT simulations, changes in future climate resulted in decreased surface runoff (9% to 22%) and increased tile flow (20% to 25%) because more precipitation occurred in smaller events, allowing more infiltration to occur. There was an increase in sediment loss for all four watersheds (ranging from 6% to 30%), while average annual soluble-P loss decreased for the CCW (10%) and F34 (25%) watersheds between the baseline period and the end of this century. Changes in atrazine, soluble-N, total-N and total-P losses were not significant at α = 0.05

Given the changes in projected future climate, the long-term impacts of both individual and combined conservation practices were assessed in the AXL watershed. The estimated average annual reductions for each decade of future climate due to conservation practices implementation ranged from 15% to 25% for surface runoff, 32% to 68% for sediment, 37% to 60% for atrazine, 5% to 13% for soluble-N, 12% to 35% for total-N, 9% to 41% for soluble-P, and 33% to 60% for total-P. Results of the study indicated that individual conservation practices were effective in reducing a targeted pollutant load, but combined practices were more effective in reducing multiple pollutant loadings simultaneously. No-till was the most effective individual conservation practice, while a combination of five conservation practices was most effective in reducing runoff, sediment, atrazine, and nitrogen and phosphorus losses.

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