Long-Term Trajectory of Nitrogen Loading and Delivery From Mississippi River Basin to the Gulf of Mexico
Date
2020-05
Authors
Tian, Hanqin
Xu, Rongting
Pan, Shufen
Yao, Yuanzhi
Bian, Zihao
Cai, Wei-Jun
Hopkinson, Charles S.
Justic, Dubravko
Lohrenz, Steven
Major Professor
Advisor
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Wiley
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.
Series Number
Journal Issue
Is Version Of
Versions
Series
Academic or Administrative Unit
Type
article
Comments
This article is published as Tian, Hanqin, Rongting Xu, Shufen Pan, Yuanzhi Yao, Zihao Bian, Wei‐Jun Cai, Charles S. Hopkinson et al. "Long‐term trajectory of nitrogen loading and delivery from Mississippi River Basin to the Gulf of Mexico." Global Biogeochemical Cycles 34, no. 5 (2020): e2019GB006475. doi:10.1029/2019GB006475.
Rights Statement
© 2020 American Geophysical Union.
Copyright
Funding
This study was supported in part by the National Science Foundation grant 1903722, the National Aeronautics and Space Administration grants NNX12AP84G, NNX14AO73G, and
NNX10AU06G, the National Oceanic and Atmospheric Administration grant NA16NOS4780204, and the OUC‐AU Joint Center Program.