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We utilize a coupled economy–agroecology–hydrology modeling framework to capture the cascading impacts of climate change mitigation policy on agriculture and the resulting water quality cobenefits. We analyze a policy that assigns a range of United States government’s social cost of carbon estimates ($51, $76, and $152/ton of CO2-equivalents) to fossil fuel–based CO2emissions. This policy raises energy costs and, importantly for agriculture, boosts the price of nitrogen fertilizer production. At the highest carbon price, US carbon emissions are reduced by about 50%, and nitrogen fertilizer prices rise by about 90%, leading to an approximate 15% reduction in fertilizer applications for corn production across the Mississippi River Basin. Corn and soybean production declines by about 7%, increasing crop prices by 6%, while nitrate leaching declines by about 10%. Simulated nitrate export to the Gulf of Mexico decreases by 8%, ultimately shrinking the average midsummer area of the Gulf of Mexico hypoxic area by 3% and hypoxic volume by 4%. We also consider the additional benefits of restored wetlands to mitigate nitrogen loading to reduce hypoxia in the Gulf of Mexico and find a targeted wetland restoration scenario approximately doubles the effect of a low to moderate social cost of carbon. Wetland restoration alone exhibited spillover effects that increased nitrate leaching in other parts of the basin which were mitigated with the inclusion of the carbon policy. We conclude that a national climate policy aimed at reducing greenhouse gas emissions in the United States would have important water quality cobenefits.
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Long‐Term Trajectory of Nitrogen Loading and Delivery From Mississippi River Basin to the Gulf of Mexico
Abstract The large areal extent of hypoxia in the northern Gulf of Mexico has been partially attributed to substantial nitrogen (N) loading from the Mississippi River basin, which is driven by multiple natural and human factors. The available water quality monitoring data and most of the current models are insufficient to fully quantify N load magnitude and the underlying controls. Here we use a process‐based Dynamic Land Ecosystem Model to examine how multiple factors (synthetic N fertilizer, atmospheric N deposition, land use changes, climate variability, and increasing atmospheric CO2) have affected the loading and delivery of total nitrogen (TN) consisting of ammonium and nitrate (dissolved inorganic N) and total organic nitrogen from the Mississippi River basin during 1901–2014. The model results indicate that TN export during 2000–2014 was twofold larger than that in the first decade of twentieth century: Dissolved inorganic N export increased by 140% dominated by nitrate; total organic nitrogen export increased by 53%. The substantial enrichment of TN export since the 1960s was strongly associated with increased anthropogenic N inputs (synthetic N fertilizer and atmospheric N deposition). The greatest export of TN was in the spring. Although the implementation of N reduction has been carried out over the past three decades, total N loads to the northern Gulf of Mexico have not decreased significantly. Due to the legacy effect from historical N accumulation in soils and riverbeds, a larger reduction in synthetic N fertilizer inputs as well as improved N management practices are needed to alleviate ocean hypoxia in the northern Gulf of Mexico.
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- Award ID(s):
- 1903722
- PAR ID:
- 10374950
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 34
- Issue:
- 5
- ISSN:
- 0886-6236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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