The impact of land-use and global change on water-related agro-ecosystem services in the midwest US
Humans have and are likely to continue to dramatically alter both the global landscape through the conversion of natural ecosystems into agriculture, and the atmosphere through the combustion of biomass and fossil fuels to meet the need for food and energy. Associated with these land use and global changes are major alterations in the biogeochemical cycles of carbon, water, and nitrogen, which have important implications on the growth and function of ecosystems and the services they provide for humanity. This dissertation investigates the impacts on water-related agro-ecosystem services associated with increasing concentrations of the tropospheric pollutant ozone ([O3]) and land use change for cellulosic feedstocks in the Midwestern United States. This study focused on quantifying changes in water-related agro-ecosystem services including direct changes to water quantity, water use efficiency (WUE) that links the carbon cycle to water, and water quality that links the nitrogen cycle to water. In the context of these land-use and global changes and the associated changes in water-related agro-ecosystem services, the goals of this research are to: 1) determine the concentration at which soybean latent heat flux (λET) is sensitive to O3, test whether decreases in λET are linked with the concentration of O3, and find whether an increase in O3 has an impact on WUE 2) determine the regional distribution of water use and WUE for Miscanthus × giganteus (miscanthus) and Panicum virgatum (switchgrass) two of the leading candidate cellulosic feedstocks, relative to Zea mays L. (maize), the current dominant ethanol feedstock 3) determine the change in streamflow in the Mississippi-Atchafalya River Basin (MARB) and the export of dissolved inorganic nitrogen (DIN) to the Gulf of Mexico hypoxic region associated with large-scale production of miscanthus and switchgrass. Micrometeorological measurements were made at the Soybean Free Air Concentration Enrichment facility to determine the sensible heat flux (H) and latent heat flux (λET) of a commercial soybean cultivar exposed to ozone concentrations ranging from current levels (ca. 40 ppb) to three times current (ca. 120 ppb). As [O3] increased from the lowest to highest level, soybean canopy λET declined and H increased. Exposure to increased [O3] also resulted in warmer canopies especially during the day. The [O3]-induced relative decline in ET was half that of the relative decline in seed yield, driving a 50% reduction in seasonal WUE. To assess the impact of land use change for bioenergy production a vegetation model (Agro-IBIS) capable of simulating the growth, function and ecosystem uptake of water and carbon and leaching of Dissolved Inorganic Nitrogren (DIN) was coupled with a hydrology model (THMB) that simulated streamflow and DIN export. Algorithms were developed for Agro-IBIS and tested for their ability to simulate miscanthus and switchgrass. Using this modeling framework a series of simulations were conducted using historical climate data throughout the 20th century with Agro-IBIS and THMB for a domain encapsulating the Midwest US and the MARB. On average, throughout the domain miscanthus used more water than any existing land cover, and switchgrass used more water than most. Miscanthus and switchgrass had higher WUE than maize throughout the region, especially when belowground carbon stored in the roots was considered. Due to increases in water use, there were reductions in runoff and streamflow in the MARB for both miscanthus and switchgrass that depended on the fractional crop coverage, with miscanthus having a larger impact than switchgrass. Differences in streamflow were largest when miscanthus replaced current crops in the driest portions of the MARB with miscanthus causing up to 6% reduction in streamflow at the highest replacement levels. Conversely differences in DIN export were more evenly distributed across the basin, with reductions up to 25% in some rivers in the highest replacement scenarios. Compared to streamflow, reductions in DIN export from the MARB to the Gulf of Mexico were several times larger depending on the fertilization application rates. These results suggest that global change and land-use-change for bioenergy production in the Midwest will alter the agro-ecosystem fluxes of carbon, water, and nitrogen that are key drivers of water related agro-ecosystem services.
land use change, global change, bioenergy, water use efficiency, ozone
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign