Reducing hypoxia in the Gulf of Mexico: Advice from three models

Scavia, Donald; Justić, Dubravko; Bierman, Victor J.

doi:10.1007/bf02803534

Cited by 107 publications

(75 citation statements)

References 19 publications

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“…The model is calibrated through Bayesian inference over the period 1985-2011 (30). The model has been compared with others (18) and was used to explore N vs. P control (76), provide guidance for the Gulf Action Plans (13,14), and explore impacts of climate change (77). The load-response curve was developed with parameter estimates for normal weather years.…”

Section: Methodsmentioning

confidence: 99%

“…The Louisiana State University/Louisiana University Marine Consortium (LSU/LUMCON) and the Virginia Institute of Marine Sciences (VIMS) models are linear regressions based on different assumptions and statistically identified relationships for the response of hypoxia to nutrients and stratification. Further details are in Methods.The benefits of using multiple models are being increasingly recognized (18)(19)(20)(21)(22)(23). Because each model is a different representation of the real world, the advantages of multiple models include viewing problems from different conceptual perspectives, testing the effects of different assumptions, and reducing decision risk (22).…”

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confidence: 99%

“…The benefits of using multiple models are being increasingly recognized (18)(19)(20)(21)(22)(23). Because each model is a different representation of the real world, the advantages of multiple models include viewing problems from different conceptual perspectives, testing the effects of different assumptions, and reducing decision risk (22).…”

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confidence: 99%

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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: 99%

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confidence: 99%

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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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“…Nu-trient loading in these habitats causes harmful algal blooms, sea grass losses, food web structure changes, increased hypoxia/anoxia events, burial disruption, and organic matter degradation (36)(37)(38)(39). Furthermore, in habitats with longer water residence times, phytoplankton chlorophyll and anoxic/hypoxic volumes are further increased in the water column (40,41). The structure of the bacterioplankton community within coastal bays has been widely studied.…”

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The Pattern of Change in the Abundances of Specific Bacterioplankton Groups Is Consistent across Different Nutrient-Enriched Habitats in Crete

Fodelianakis

Papageorgiou

Pitta

et al. 2014

Appl Environ Microbiol

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A common source of disturbance for coastal aquatic habitats is nutrient enrichment through anthropogenic activities. Although the water column bacterioplankton communities in these environments have been characterized in some cases, changes in ␣-diversity and/or the abundances of specific taxonomic groups across enriched habitats remain unclear. Here, we investigated the bacterial community changes at three different nutrient-enriched and adjacent undisturbed habitats along the north coast of Crete, Greece: a fish farm, a closed bay within a town with low water renewal rates, and a city port where the level of nutrient enrichment and the trophic status of the habitat were different. Even though changes in ␣-diversity were different at each site, we observed across the sites a common change pattern accounting for most of the community variation for five of the most abundant bacterial groups: a decrease in the abundance of the Pelagibacteraceae and SAR86 and an increase in the abundance of the Alteromonadaceae, Rhodobacteraceae, and Cryomorphaceae in the impacted sites. The abundances of the groups that increased and decreased in the impacted sites were significantly correlated (positively and negatively, respectively) with the total heterotrophic bacterial counts and the concentrations of dissolved organic carbon and/or dissolved nitrogen and chlorophyll ␣, indicating that the common change pattern was associated with nutrient enrichment. Our results provide an in situ indication concerning the association of specific bacterioplankton groups with nutrient enrichment. These groups could potentially be used as indicators for nutrient enrichment if the pattern is confirmed over a broader spatial and temporal scale by future studies.

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“…Hypoxia (, 2 mg O 2 L 21 ) develops in bottom waters as a synergistic product of high stability of the water column and nutrient-enhanced surface productivity, which is manifested in a high vertical carbon flux that fuels benthic and water-column respiration (Rabalais and Turner 2001). Model hindcasts suggest that large hypoxic regions were likely not present prior to the mid1970s (Justić et al 2001;Scavia et al 2004;Turner et al 2006), when the use of nitrogen-based fertilizer in the Mississippi River watershed increased dramatically (Turner and Rabalais 1991;Boesch 2002). The severity of summer hypoxia (usually mapped in late July; Rabalais et al 2007) varies annually due to its tight coupling to freshwater and nutrient fluxes of the Mississippi and Atchafalaya Rivers (Turner et al 2006(Turner et al , 2008.…”

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confidence: 99%

Effects of biological and physical factors on seasonal oxygen dynamics in a stratified, eutrophic coastal ecosystem

Rivera

Wissel

Rabalais

et al. 2009

Limnology & Oceanography

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Using a dual-budget approach based on oxygen concentrations and stable isotopes, we examined primary production, respiration, and production to respiration ratios (P : R) across the Louisiana continental shelf to determine the relative roles of biological and physical factors in controlling seasonal oxygen dynamics. Regression models for d 18 O and P : R indicated that the concentration of algal biomass explained most of the variability of the seasonal oxygen dynamics in surface waters. Physical factors, such as salinity, temperature, water-column stability, and station depth were only of minor importance. Seasonal oxygen dynamics were more pronounced in bottom waters than in surface waters as hypoxia was common in bottom waters during summer months (MayOctober). During cooler winter months (November-April), oxygen concentrations throughout the water column were close to equilibrium with the atmosphere. The relative importance of benthic respiration to water-column respiration in bottom waters was more pronounced during summer months when the water column was stratified.

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Reducing hypoxia in the Gulf of Mexico: Advice from three models

Cited by 107 publications

References 19 publications

Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

The Pattern of Change in the Abundances of Specific Bacterioplankton Groups Is Consistent across Different Nutrient-Enriched Habitats in Crete

Effects of biological and physical factors on seasonal oxygen dynamics in a stratified, eutrophic coastal ecosystem

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