Declining Threshold for Hypoxia in the Gulf of Mexico

Stow, Craig A.; Qian, Song S.; Craig, J. Kevin

doi:10.1021/es049412o

Cited by 36 publications

(18 citation statements)

References 45 publications

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“…Similar trends are most obvious from the 1990s to present in cores from the southwest Louisiana coast. The long-term changes in paleoindicators are consistent with the observational data on hypoxia (Rabalais et al 2002b, Stow et al 2005, Rabalais and Turner 2006 and coincident with the well-documented increase in nitrate export from the Mississippi River (Fig. 4).…”

Section: Synthesissupporting

confidence: 86%

Sediments Tell the History of Eutrophication and Hypoxia in the Northern Gulf of Mexico

Rabalais

Turner

Gupta

et al. 2007

Ecological Applications

163

108

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Abstract. We examined a suite of paleoindicators in 210 Pb-dated sediment cores to determine the historical course of primary production, eutrophication, and oxygen stress in the coastal ocean adjacent to the plumes of the Mississippi and Atchafalaya rivers. The assumption that hypoxia is a natural feature of the coastal ecosystem in the northern Gulf of Mexico influenced by the discharge of the Mississippi River system is not supported by paleoindicators in accumulated sediments. There is a propensity for the ecosystem to develop hypoxia because of the high discharge of the Mississippi River and physical dynamics on the continental shelf that support stratification. However, paleoindicators of eutrophication and oxygen conditions record recent anthropogenic influences. The evidence for increased carbon production and accumulation comes from diatoms and their remnants, marine-origin carbon in the sediments, and phytoplankton pigments. Surrogates for oxygen condition, including mineral, isotopic, microfossil, and phytoplankton pigment indicators, indicate worsening oxygen stress. The changes are more apparent in areas of present chronic hypoxia and are coincident with the increasing nitrogen loads from the Mississippi River system beginning in the 1950s. Longer-term shifts in offshore ecology parallel landscape changes within the watershed in the last two centuries. The temporal shifts in this coastal ecosystem parallel the time sequence of similarly eutrophied coastal waters globally and coincide nicely with sediment analyses from other locations.

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Section: Synthesissupporting

confidence: 86%

Sediments Tell the History of Eutrophication and Hypoxia in the Northern Gulf of Mexico

Rabalais

Turner

Gupta

et al. 2007

Ecological Applications

163

108

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“…4). The benefits of the Bayesian modeling framework have been demonstrated in previous hypoxia modeling studies by Liu et al (2010) and Stow et al (2005), and this study builds on that work by applying the Bayesian framework to a richer mechanistic model, capable of integrating a larger suite of environmental inputs. In addition, this is the first Gulf hypoxia modeling study to systematically test the model's predictive performance for observations not included within the calibration data set (using CV).…”

Section: Discussionmentioning

confidence: 91%

Assessing biophysical controls on Gulf of Mexico hypoxia through probabilistic modeling

Obenour

Michalak

Scavia

2015

Ecological Applications

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A mechanistic model was developed to predict midsummer bottom-water dissolved oxygen (BWDO) concentration and hypoxic area on the Louisiana shelf of the northern Gulf of Mexico, USA (1985-2011). Because of its parsimonious formulation, the model possesses many of the benefits of simpler, more empirical models, in that it is computationally efficient and can rigorously account for uncertainty through Bayesian inference. At the same time, the model incorporates important biophysical processes such that its parameterization can be informed by field-measured biological and physical rates. The model is used to explore how freshwater flow, nutrient load, benthic oxygen demand, and wind velocity affect hypoxia on the western and eastern sections of the shelf, delineated by the Atchafalaya River outfall. The model explains over 70% of the variability in BWDO on both shelf sections, and outperforms linear regression models developed from the same input variables. Model results suggest that physical factors (i.e., wind and flow) control a larger portion of the year-to-year variability in hypoxia than previously thought, especially on the western shelf, though seasonal nutrient loads remain an important driver of hypoxia, as well. Unlike several previous Gulf hypoxia modeling studies, results do not indicate a temporal shift in the system's propensity for hypoxia formation (i.e., no regime change). Results do indicate that benthic oxygen demand is a substantial BWDO sink, and a better understanding of the long-term dynamics of this sink is required to better predict how the size of the hypoxic zone will respond to proposed reductions in nutrient loading.

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“…Summer hypoxia has also been observed on the inner continental shelf of the northwest Gulf of Mexico west of the Mississippi River Delta (the ''dead zone'') over the last century (Rabalais et al, 1994(Rabalais et al, , 2002Rowe, 2001;Stow et al, 2005). This area is significantly deeper ($5-60 m) than the Corpus Christi Bay site and hypoxia persists below the pycnocline because of freshwater run-off from the Mississippi River.…”

Section: Study Sitesmentioning

confidence: 99%

Dissolved Fe2+ and ∑H2S Behavior in Sediments Seasonally Overlain by Hypoxic-to-anoxic Waters as Determined by CSV Microelectrodes

Sell

Morse

2006

Aquat Geochem

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Variability of dissolved Fe 2+ and P H 2 S concentrations in porewaters were studied, using cathodic stripping voltammetry (CSV) microelectrodes, in sediments overlain by hypoxic waters in the summer from the southeastern region of Corpus Christi Bay, Texas (CCB) and the Mississippi River Bight (MRB), Louisiana. These measurements were complimented by sediment microcosm studies where oxygen concentrations in the overlying water were manipulated. Sulfate reduction rates, benthic oxygen demand, total reduced sulfide, porewater sulfate, and total organic carbon were also determined. Fe 2+ and P H 2 S were the major dissolved redox-reactive dissolved species in these sediments. During hypoxic conditions, an upward migration of porewater Fe 2+ and P H 2 S occurred, with Fe 2+ reaching much higher maximum concentrations than P H 2 S. Statistically significant (p<0:05) differences in both Fe 2+ and P H 2 S occurred between sediments at the CCB and MRB study sites. Although both sites were Fe-dominated, reactive and dissolved iron were higher while P H 2 S was lower at the MRB site. However, there were no statistically significant (p > 0:05) difference in regard to P H 2 S between microcosm and field monitoring studies. Results indicated that, for Fe 2+ and P H 2 S, relatively large and rapid changes occurred in both the concentrations and distributions of these important porewater constituents in response to relatively short-term changes in overlying water oxygen content. Model calculations indicated that conditions in the sediments can be responsible for the induction of hypoxic conditions in the formation of hypoxic overlying waters in <6 days at CCB and $20 days at MRB.

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Declining Threshold for Hypoxia in the Gulf of Mexico

Cited by 36 publications

References 45 publications

Sediments Tell the History of Eutrophication and Hypoxia in the Northern Gulf of Mexico

Sediments Tell the History of Eutrophication and Hypoxia in the Northern Gulf of Mexico

Assessing biophysical controls on Gulf of Mexico hypoxia through probabilistic modeling

Dissolved Fe2+ and ∑H2S Behavior in Sediments Seasonally Overlain by Hypoxic-to-anoxic Waters as Determined by CSV Microelectrodes

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