Assessing the response mechanisms of elevated CO2 concentration on various forms of nitrogen losses in the Golden Corn Belt

Authors: ZHANG, YINGGI - China Agricultural University; HAN, YIWEN - China Agricultural University; WEN, NA - China Agricultural University; QI, JUNYU - University Of Maryland; ZHANG, XIAOYU - China Agricultural University; Marek, Gary; SRINIVASAN, RAGHAVAN - Texas A&M University; FENG, PUYU - China Agricultural University; LIU, DE LI - Wagga Wagga Agricultural Institute; HU, KELIN - China Agricultural University; CHEN, YONG - China Agricultural University

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2024
Publication Date: 7/15/2024
Citation: Zhang, Y., Han, Y., Wen, N., Qi, J., Zhang, X., Marek, G.W., Srinivasan, R., Feng, P., Liu, D., Hu, K., Chen, Y. 2024. Assessing the response mechanisms of elevated CO2 concentration on various forms of nitrogen losses in the Golden Corn Belt. Water Resources Research. 60. Article e2024WR037226. https://doi.org/10.1029/2024WR037226.
DOI: https://doi.org/10.1029/2024WR037226

Interpretive Summary: Increases in atmospheric CO2 concentration associated with climate change may pose a substantial risk to global food security and water quality in alluvial agricultural crop production regions such as the Upper Mississippi River Basin (UMRB). Specifically, the effects of increased CO2 concentration on crop nitrogen (N) requirements and nutrient cycling are uncertain. Computer simulation modeling incorporating general circulation models and shared socioeconomic pathways may help identify interactions between CO2 concentration and N cycling dynamics that could be used to develop management strategies to reduce N losses. The Soil and Water Assessment Tool (SWAT) is a widely used watershed scale model but only allows for a static CO2 concentration value. However, researchers from USDA-ARS Bushland and university partners from the U.S., Australia, and China used a modified SWAT model equipped with a dynamic CO2 concentration algorithm to simulate N cycling in the UMRB under future climate scenarios. Simulations using the improved SWAT model suggested increased risk of multiple forms of N losses occurring under projected elevated CO2 concentrations with greater losses through nitrate leaching than for sediment erosion and runoff. Proposed mitigation strategies included adjusting plant N stress triggers 10-20 percent depending on location within the UMRB watershed.

Technical Abstract: Nitrogen (N) loss is a significant source of water quality pollution in agricultural watersheds. Elevated CO2 concentration (eCO2) can have multiple effects on the N cycle, while the complex mechanisms linking N loss and eCO2 are not well recognized. In this study, we applied a calibrated Soil and Water Assessment Tool (SWAT) model with the CO2 dynamic input and response module to investigate the complex response mechanisms between multiform N losses (organic N loss through sediment, nitrate loss via runoff, and nitrate leaching) and eCO2 in the Upper Mississippi River Basin (UMRB; 492,000 km 2). Results revealed great spatial heterogeneity of nitrogen loss from north to south across 14 zones in the UMRB under eCO2, with nitrate loss exceeding 100 percent in some upstream zones under the SSP5-8.5 scenario compared to the constant CO2 concentration (cCO2). Furthermore, under this severe emission scenario, N loss increased gradually from 2041 to 2100 under eCO2 and differed significantly from the other SSP and cCO2 scenarios towards the end of the 21st century. When N loss was further quantitatively projected for future periods (2041-2070 and 2071-2100), we found that nitrate leaching was higher than the other two forms, peaking at 309.3 percent, as compared to the baseline period (1985-2014). In order to reduce the risk of N loss, optimization scenarios of N loss through the reduction of N fertilizer were set up. The findings suggested reducing fertilizer inputs was promising, especially for reducing nitrate loss through runoff and leaching by up to 17.7 and 12.2 percent, respectively. This study explored the mechanisms of N loss in response to eCO2, highlighting the urgency of adopting comprehensive and sustainable N management strategies, and providing reliable scientific evidence for making decisions to improve water quality and ecological sustainability at a large watershed scale.