Understanding Gulf of America Hypoxia Using CMAQ
Elevated reactive nitrogen (N) loading from the air and land to receiving waters can result in large algae “blooms.” When these blooms eventually mature, die and sink to the ocean floor, the decay process can result in transient areas of depleted oxygen in bottom waters, i.e., hypoxiaLow oxygen content or tension; deficiency of oxygen in the inspired air. Hypoxia can lead to the exodus of mobile marine species from the area. Less mobile species experience stress or death under hypoxic conditions. The U.S. Northern Gulf of America (NGA) experiences recurring/annual hypoxic events that can last several months and, from 2011-2015 averaged more than 13,000 km2 in extent (Rabotyagov et al., 2014; Turner et al., 2012).
The Mississippi River Basin (MRB) is the dominant source of freshwater to the NGA, and agricultural sources of nutrients within the MRB have also been identified as key contributors to excess nutrient loading to the NGA (Robertson et al., 2013). Meeting future demand for food, feed and bioenergy through expansion of MRB agricultural production could increase already excessive N and phosphorous (P) loads to the NGA if practicable means of capturing or reducing edge-of-field nutrient losses cannot be found (Donner and Kucharik, 2008; Costello, et al., 2009; Alshawaf et al., 2016).
Identifying land management strategies which reduce the extent and intensity of annual hypoxic events in the NGA, while sustaining the long-term economic, societal and ecological health of land, air and water environments in the MRB, represents a critical regional-scale research challenge. Comparisons of a baseline environmental status representing present conditions to two future scenarios (2022) that reflect continued emission reductions prescribed under the Clean Air Act (CAA), and increasing atmospheric carbon dioxide (CO2) concentrations with and without expanded bioenergy feedstock production, assumed here to be grain corn are used to identify and explore these strategies.
Stakeholder interests are represented by energy and agricultural market price-driven land use change and changing environmental exposures (e.g., nitrate in groundwater). Air quality status is simulated with bi-directional CMAQ, land quality status and the production of food and animal and bio-energy feedstocks are simulated using the coupled EPIC/CMAQ modeling system, i.e. the Fertilizer Emission Scenario Tool for CMAQ (FEST-C) system (Ran et al., 2018), and changes to nutrient loads transported to the NGA are simulated using a large watershed model (McCracken, et al., 2017). The synthesis of stakeholder (market) and multi-media environmental results, provides a more holistic picture of known and unanticipated challenges as well as solutions to hypoxia in our Southern Coastal waters.
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References
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Cooter, E.J., Dodder, R., Bash, J., Ran, L., Benson, V., Yang, D., & Dennis, R. (submitted). Loose coupling of economic and physical process models supporting integrated multimedia research in the United States Mississippi River Basin.
Costello, C., Griffin, W.M., Landis, A.E., & Matthews, H.S. (2009). Impact of biofuel crop production on the formation of hypoxia in the Gulf of Mexico. Environ. Sci. Technol, 43, 7985-7991.
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Garcia, V., Cooter, E.J., Hinckley, B., Murphy, M., Xing, X., Crooks, J. (2017). Examining the impacts of increased corn production on ground water quality using a coupled modelling system. Science of the Total Environment, 586, 16-24. doi: 10.1016/j.scitotenv.2017.02.009.
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Rabotyagov, S.S., Kling, C.L., Gassman, P.W., Rabalais, N.N., & Turner, R.E. (2014). The Economics of dead zones: causes, impacts, policy challenges and a model of the Gulf of Mexico Hypoxic Zone. Review of Environmental Economics and Policy 8, 58-79. doi: 10.1093/reep/ret024
Ran, L., Cooter, E., Yang, D., Benson, V., Yuan, Y., Hanna, A. and Val, G., 2018. User’s Guide for the Fertilizer Emission Scenario Tool for CMAQ (FEST-C) Version 1.4. Community Modeling and Analysis System. NOTE: Review and QA of all work products is included with the hours for those work products (cmascenter.org)
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