A Preliminary Mass Balance Model of Primary Productivity and Dissolved Oxygen in the Mississippi River Plume/Inner Gulf Shelf Region

Bierman, Victor J.; Hinz, Scott C.; Dongwei, Zhu; Wiseman, William J.; Rabalais, Nancy N.; Turner, R. Eugene

doi:10.2307/1352756

Cited by 108 publications

(53 citation statements)

References 17 publications

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“…The second and third terms represent advection by currents in the east-west and north-south directions respectively. In box models, flow data from field observations or from prognostic three-dimensional models of ocean circulation are required to represent advection by currents at the boundaries (Cerco and Cole, 1993;Bierman et al, 1994 transport by upwelling or downwelling. The fifth term represents vertical mixing in which K z (x,y,z) is the vertical eddy diffusivity.…”

Section: Advective-dispersive Transport Processesmentioning

confidence: 99%

“…This approach is potentially misleading, as oxygen demand in the lower water column can be not only substantial but also out of phase with the oxygen demand in the sediment. In the Gulf of Mexico, for example, simulations suggest that the SOD contributes between 22% and 73% of the total oxygen consumption in the lower water column (Bierman et al, 1994). In addition, during seasonal hypoxia, the locus of oxygen consumption may shift upwards, from the sediment into the water column (Eldridge and Morse, 2008).…”

Section: Dynamic Coupling Between Sediment and Water Columnmentioning

confidence: 99%

“…Justić et al (1996Justić et al ( , 2002) simulated oxygen dynamics at one location within the hypoxic zone, using a model that has two vertical layers and is forced by meteorological data and nitrogen loading from the MississippiAtchafalaya Rivers. Bierman et al (1994) simulated the steady-state summertime conditions for the hypoxic area using a three-dimensional mass balance model that takes into account some of the interactions between food web processes, nutrients, and oxygen. The model studies of Justić et al (2002) suggest that a long-term increase in riverine nutrient fluxes has been responsible for the historical decrease in bottom layer oxygen concentrations in this region Similarly, the Bierman et al (1994) model indicates that chemical-biological processes appear to be relatively more important than advective-dispersive transport processes in controlling bottom-water dissolved-oxygen dynamics.…”

Section: Northern Gulf Of Mexicomentioning

confidence: 99%

“…Bierman et al (1994) simulated the steady-state summertime conditions for the hypoxic area using a three-dimensional mass balance model that takes into account some of the interactions between food web processes, nutrients, and oxygen. The model studies of Justić et al (2002) suggest that a long-term increase in riverine nutrient fluxes has been responsible for the historical decrease in bottom layer oxygen concentrations in this region Similarly, the Bierman et al (1994) model indicates that chemical-biological processes appear to be relatively more important than advective-dispersive transport processes in controlling bottom-water dissolved-oxygen dynamics. Eldridge and used a non steady state data driven numeric benthic-pelagic model to investigate the role of sediment and water column metabolism in the development of hypoxia on the Louisiana shelf.…”

Section: Northern Gulf Of Mexicomentioning

confidence: 99%

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Modeling dissolved oxygen dynamics and hypoxia

et al. 2010

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Abstract. Hypoxia conditions are increasing throughout the world, influencing biogeochemical cycles of elements and marine life. Hypoxia results from complex interactions between physical and biogeochemical processes, which can not be understood by observations alone. Models are invaluable tools at studying system dynamics, generalizing discrete observations and predicting future states. They are also useful as management tools for evaluating site-specific responses to management scenarios. Here we review oxygen dynamics models that have significantly contributed to a better understanding of the effects of natural processes and human perturbations on the development of hypoxia, factors controlling the extent and temporal variability of coastal hypoxia, and the effects of oxygen depletion on biogeochemical cycles. Because hypoxia occurs in a variety of environments and can be persistent, periodic or episodic, models differ significantly in their complexity and temporal and spatial resolution. We discuss the progress in developing hypoxia models for benthic and pelagic systems that range from simple box models to three dimensional circulation models. Applications of these models in five major hypoxia regions are presented. In the last decades, substantial progress has been made towards the parameterization of biogeochemical processes in both hypoxic water columns and sediments. In coastal regions, semiempirical models have been used more frequently than mechanistic models to study nutrient enrichment and hypoxia relationships. Recent advances in three-dimensional coupled physical-ecological-biogeochemical models have allowed a better representation of physical-biological interactions in these systems. We discuss the remaining gaps in process deCorrespondence to: M. A. Peña (angelica.pena@dfo-mpo.gc.ca) scriptions and suggest directions for improvement. Better process representations in models will help us answer several important questions, such as those about the causes of the observed worldwide increase in hypoxic conditions, and future changes in the intensity and spread of coastal hypoxia. At the same time, quantitative model intercomparison studies suggest that the predictive ability of our models may be adversely affected by their increasing complexity, unless the models are properly constrained by observations.

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Section: Advective-dispersive Transport Processesmentioning

confidence: 99%

Section: Dynamic Coupling Between Sediment and Water Columnmentioning

confidence: 99%

Section: Northern Gulf Of Mexicomentioning

confidence: 99%

Section: Northern Gulf Of Mexicomentioning

confidence: 99%

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Modeling dissolved oxygen dynamics and hypoxia

et al. 2010

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“…We use a biophysical model to explore the relative influence of nitrogen load and ocean variability on changes in hypoxia and provide hindcasts and forecasts of hypoxic area in response to changes in loads, bounded by ranges in potential ocean conditions. Although efforts to model the interactions between nutrient load and oxygen dynamics have successfully simulated temporal variability within one vertical dimension (e.g., Justić et al 1996Justić et al , 1997Justić et al , 2002 and three dimensions (Bierman et al 1994), this model is the first to successfully predict the direct effect of variable nutrient loads on the areal extent of hypoxia on this shelf.…”

Section: Acknowledgmentsmentioning

confidence: 99%

Untitled

2003

Limnology & Oceanography

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The effects of nutrient loading from the Mississippi River basin on the areal extent of hypoxia in the northern Gulf of Mexico were examined using a novel application of a dissolved oxygen model for a river. The model, driven by river nitrogen load and a simple parameterization of ocean dynamics, reproduced 17 yr of observed hypoxia location and extent, subpycnocline oxygen consumption, and cross-pycnocline oxygen flux. With Monte Carlo analysis, we illustrate through hindcasts back to 1968 that extensive regions of low oxygen were not common before the mid-1970s. The Mississippi River Watershed/Gulf of Mexico Hypoxia Task Force set a goal to reduce the 5-yr running average size of the Gulf's hypoxic zone to less than 5,000 km 2 by 2015 and suggested that a 30% reduction from the 1980-1996 average nitrogen load is needed to reach that goal. Here we show that 30% might not be sufficient to reach that goal when year-to-year variability in ocean dynamics is considered.

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Temporal variation and stoichiometric ratios of organic matter remineralization in bottom waters of the northern Gulf of Mexico during late spring and summer

Xue

Cai

et al. 2015

JGR Oceans

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An improved extended optimum multiparameter (eOMP) analysis was applied to hydrographic (temperature and salinity), and water chemistry data, including dissolved oxygen (O2), nutrients (nitrate plus nitrite, phosphate, and silicate), dissolved inorganic carbon (DIC), and total alkalinity (TAlk) data collected during late spring and summer from 2006 to 2012 in bottom waters off the Louisiana coast, to explore the dynamics and stoichiometry of DIC production during the development and maintenance of summer hypoxia. Our analysis demonstrated that DIC in bottom water was relatively low from April to June, but increased significantly in July, peaked in August, and dropped slightly in September. Furthermore, DIC production resulted from both aerobic organic carbon (OC) respiration and denitrification, as well as substantial loss due to vertical mixing with surface water. The average summer gross OC respiration rate was estimated to be 0.19 g C m−2 d−1, with the highest values occurring in late summer when hypoxic conditions dominated. We also found that Corg/N/P/‐O2 remineralization ratios for aerobic respiration were generally consistent with the classic Redfield ratio (106/16/1/138) except individual C/N and C/P ratios were slightly lower, indicating that marine OC was the major source of the DIC production in the bottom water. This study quantified the role of temporal bottom‐water microbial respiration to seasonal DIC dynamics and provided a means for studying the stoichiometry of biogeochemical processes in coastal waters.

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A Preliminary Mass Balance Model of Primary Productivity and Dissolved Oxygen in the Mississippi River Plume/Inner Gulf Shelf Region

Cited by 108 publications

References 17 publications

Modeling dissolved oxygen dynamics and hypoxia

Modeling dissolved oxygen dynamics and hypoxia

Untitled

Temporal variation and stoichiometric ratios of organic matter remineralization in bottom waters of the northern Gulf of Mexico during late spring and summer

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