Gulf of Mexico Hypoxia: Exploring Increasing Sensitivity to Nitrogen Loads

Liu, Yong; Evans, Mary Anne; Scavia, Donald

doi:10.1021/es903521n

Cited by 43 publications

(55 citation statements)

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“…Previous studies suggested no apparent correlation between hypoxic area (or predictive errors) in 1 y and either N load or hypoxic extent in the previous year. Thus, including predictors representing carryover effects from the previous year did not substantially improve model fit (31,35,69). The loads used by each model show similar interannual patterns (Fig.…”

Section: Methodsmentioning

confidence: 88%

Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

Scavia

Bertani

Obenour

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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A large region of low-dissolved-oxygen bottom waters (hypoxia) forms nearly every summer in the northern Gulf of Mexico because of nutrient inputs from the Mississippi River Basin and water column stratification. Policymakers developed goals to reduce the area of hypoxic extent because of its ecological, economic, and commercial fisheries impacts. However, the goals remain elusive after 30 y of research and monitoring and 15 y of goal-setting and assessment because there has been little change in river nitrogen concentrations. An intergovernmental Task Force recently extended to 2035 the deadline for achieving the goal of a 5,000-km 2 5-y average hypoxic zone and set an interim load target of a 20% reduction of the spring nitrogen loading from the Mississippi River by 2025 as part of their adaptive management process. The Task Force has asked modelers to reassess the loading reduction required to achieve the 2035 goal and to determine the effect of the 20% interim load reduction. Here, we address both questions using a probabilistic ensemble of four substantially different hypoxia models. Our results indicate that, under typical weather conditions, a 59% reduction in Mississippi River nitrogen load is required to reduce hypoxic area to 5,000 km 2 . The interim goal of a 20% load reduction is expected to produce an 18% reduction in hypoxic area over the long term. However, due to substantial interannual variability, a 25% load reduction is required before there is 95% certainty of observing any hypoxic area reduction between consecutive 5-y assessment periods.ensemble modeling | hypoxia | Gulf of Mexico | nitrogen-loading targets A large region of low-dissolved-oxygen (DO) bottom waters (hypoxia; DO < 2 mg·L −1 ) has formed nearly every summer in the Gulf of Mexico for at least the last three decades (1-3). Hypoxia forms because of respiration of organic matter in bottom waters and a vertically stratified water column restricting reaeration (4-6). Both factors are related to the outflow of freshwater and nutrients from the Mississippi River Basin, which typically peaks in March through May. Nutrients stimulate phytoplankton production, much of which settles in early summer, and bottom water DO (BWDO) is consumed during its decomposition. River outflows create a fresher, warmer surface layer above a colder, saltier bottom layer, limiting the vertical diffusion of DO (2).Policymakers developed hypoxia reduction goals because of ecological, economic, and commercial fisheries impacts (7-10). However, the goals remain elusive after >30 y of research and monitoring (3, 11) and >15 y of assessment and goal-setting (5, 12-16). A Gulf Task Force recently agreed to retain the 5-y moving average goal of a 5,000-km 2 hypoxic zone, but extended the deadline from 2015 to 2035 (17). The timeframe was reset because the 2015 hypoxic zone was 16,760 km 2 and the most recent 5-y average was 14,024 km 2 -greater than the long-term average of 13,751 km 2 (1). Missing the goal was not unexpected because the 5-y average load of late sp...

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Section: Methodsmentioning

confidence: 88%

Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

Scavia

Bertani

Obenour

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…We divided our correlation analysis into two periods: the longer was from 1985-2010, the shorter was from 1993-2010. The shorter period begins with 1993, i.e., the year in which the relationship between hypoxic area and riverine N-loading was reported to have changed [Turner et al, 2008;Greene et al, 2009;Liu et al, 2010;Forrest et al, 2011]. [7] The predictors in our single and multiple regression analyses are: the new variable t Uwind (defined below), the 11-month averaged MR flow ( F 11 ) [Wiseman et al, 1997], the averaged spring flow ( F spring ; April, May and June), the averaged May flow ( F May ) [Greene et al, 2009], the May NO 3+2 loading [Turner et al, 2006] and the combined MayJune NO 3+2 loading [Donner and Scavia, 2007].…”

Section: Methodsmentioning

confidence: 99%

“…Scavia et al [2003] reproduced the hypoxic area by using a one-dimensional model driven by the May-June total N-loading from the MAR. Liu et al [2010] improved the predictions of this model by incorporating an additional parameter to describe a system change in 1993. The above models were the basis of the hypoxia management strategy [Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, 2001Force, , 2008.…”

Section: Introductionmentioning

confidence: 99%

Relative role of wind forcing and riverine nutrient input on the extent of hypoxia in the northern Gulf of Mexico

Feng¹,

DiMarco

Jackson

2012

Geophysical Research Letters

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[1] Seasonal hypoxia of the northern Gulf of Mexico has been observed for more than 25 years. It is generally accepted that the variation in the areal extent of hypoxia is determined by changes in nutrient addition from the Mississippi River. In this study, we investigate the statistical relation between the hypoxic area and a new variable, the duration of west wind, using the available measurements for the period 1985-2010. Special consideration was paid to the 1993-2010 period, a time when a large shift in the seasonal hypoxia pattern has been reported. When excluding the years in which hurricanes directly impacted the hypoxic area observation, we find that the duration of west wind is correlated with the hypoxic area at r 2 = 0.32 for the 1985-2010 period, and r 2 = 0.52 for the 1993-2010 period. Multilinear regressions using both wind duration and May-June nitrate loading improve the statistical relationships for both periods to r 2 = 0.69 and 0.74 for the long and short time periods, respectively. Mechanistically, the statistical relationships reflect the movement and changes in horizontal river plume position associated with the wind and the influence of stratification on the hypoxic area. Citation: Feng, Y., S. F. DiMarco, and G. A.Jackson (2012), Relative role of wind forcing and riverine nutrient input on the extent of hypoxia in the northern Gulf of Mexico, Geophys. Res. Lett., 39, L09601,

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“…Examples include Scavia et al (2003), Scavia and Donnelly (2007), and Liu et al (2010). Calibration of parameters of the model by year has produced good fit to the observed hypoxia area (88 percent of variability explained in Scavia et al (2003), and 99 percent explained in Liu et al (2010) using Bayesian calibration techniques. All of these models focus on nitrogen.…”

Section: Linking the Size Of The Zone To Its Inputs: The Gulf Of mentioning

confidence: 99%

The Economics of Dead Zones: Causes, Impacts, Policy Challenges, and a Model of the Gulf of Mexico Hypoxic Zone

Rabotyagov¹,

Kling²,

Gassman³

et al. 2014

Review of Environmental Economics and Policy

136

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The purpose of this review and analysis is to provide a basic understanding of the issues related to worldwide hypoxic zones and the range of economic questions sorely in need of answers. We begin by describing the causes and extent of hypoxic zones worldwide, followed by a review of the evidence concerning ecological effects of the condition and impacts on ecosystem services. We describe what is known about abatement options and cost effective policy design before turning to an analysis of the large, seasonally recurring hypoxic zone in the Gulf of Mexico. We advance the understanding of this major ecological issue by estimating the relationship between pollutants (nutrients) and the areal extent of the hypoxic zone. This "production function" relationship suggests that both instantaneous and legacy contributions of nutrients contribute to annual predictions of the size of the zone, highlighting concerns that ecologists have raised about lags in the recovery of the system and affirms the importance of multiple nutrients as target pollutants. We conclude with a discussion of critical research needs to provide input to policy formation. The Economics of Dead Zones: Linking Externalities from the Land to their Consequences in the SeaOctober 17, 2012 S. S. Rabotyagov, C.L. Kling, P.W. Gassman, N.N. Rabalais, and R.E. TurnerAbstract: The purpose of this review and analysis is to provide a basic understanding of the issues related to worldwide hypoxic zones and the range of economic questions sorely in need of answers. We begin by describing the causes and extent of hypoxic zones worldwide, followed by a review of the evidence concerning ecological effects of the condition and impacts on ecosystem services. We describe what is known about abatement options and cost effective policy design before turning to an analysis of the large, seasonally recurring hypoxic zone in the Gulf of Mexico. We advance the understanding of this major ecological issue by estimating the relationship between pollutants (nutrients) and the areal extent of the hypoxic zone. This "production function" relationship suggests that both instantaneous and legacy contributions of nutrients contribute to annual predictions of the size of the zone, highlighting concerns that ecologists have raised about lags in the recovery of the system and affirms the importance of multiple nutrients as target pollutants. We conclude with a discussion of critical research needs to provide input to policy formation.

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Gulf of Mexico Hypoxia: Exploring Increasing Sensitivity to Nitrogen Loads

Cited by 43 publications

References 44 publications

Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

Relative role of wind forcing and riverine nutrient input on the extent of hypoxia in the northern Gulf of Mexico

The Economics of Dead Zones: Causes, Impacts, Policy Challenges, and a Model of the Gulf of Mexico Hypoxic Zone

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