Assessing Carbon and Water Dynamics in Multiple Agricultural Ecosystems in the Inland Pacific Northwest Using the Eddy Covariance Method and the CropSyst-Microbasin Model

Thesis (Ph.D.), Civil Engineering, Washington State UniversityManagement practices and climatic conditions have important impacts on carbon and water dynamics in agricultural ecosystems. In addition, future climate projections for the inland Pacific Northwest (iPNW) of the U.S. show a likely increase in temperature and significant reductions in precipitation that will affect carbon and water cycling. Based on the feedbacks between climate and agriculture, there is a critical need to quantify carbon and water budgets in agricultural ecosystems to better understand their distribution, cycles, and how they are impacted by different management practices and the changing climatic conditions. Carbon and water flux data at five different agricultural sites (up to thirteen site-years) covering a large precipitation gradient and a variety of management practices and crop species were measured using the eddy covariance method and simulated using the CropSyst-Microbasin model. During the period of October 2012-September 2015, both measurements and simulations showed that the winter wheat fields were net carbon sinks and the spring crops were either carbon sinks or sources, or close to carbon neutral. The carbon sink strength and identification of carbon sink/source strongly depends on crop species, climatic conditions, and management practices. Based on measurements and simulations, comparisons of carbon and water budgets over the multiple site-years implied that carbon and water losses from agriculture can be mitigated at a rain-fed site in a low-rainfall area, but can be enhanced at an irrigated site. No-till benefits of reduced carbon emissions and evaporation were consistently seen over three continuous crop years with the crop rotation of spring garbanzo, winter wheat, spring canola, therefore suggesting no-till benefits of mitigating CO2 emissions from agriculture and improving water use efficiency. Other factors, such as seeding dates, tillage fallow, weeds, and water stress, also affected agricultural carbon and water budgets via different biophysical processes.Washington State University, Civil Engineerin