A modeling study examining the impact of nutrient boundaries on primary production on the Louisiana continental shelf

Pauer, James J.; Feist, Timothy J.; Anstead, Amy M.; DePetro, Phillip A.; Melendez, Wilson; Lehrter, John C.; Murrell, Michael C.; Zhang, Xiaomi; Ko, Dong S.

doi:10.1016/j.ecolmodel.2016.02.007

Cited by 5 publications

(17 citation statements)

References 37 publications

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“…Model Changes. We applied GoMDOM to the study area (Figure 1), making several changes compared to the Pauer et al 15 model: (1) the model grid was enlarged, (2) an updated version of the hydrodynamic model was used, and (3) model kinetics were revised including adding a new sediment organic matter remineralization formulation.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Modeling the Relative Importance of Nutrient and Carbon Loads, Boundary Fluxes, and Sediment Fluxes on Gulf of Mexico Hypoxia

Feist

Pauer

Melendez³

et al. 2016

Environ. Sci. Technol.

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The Louisiana continental shelf in the northern Gulf of Mexico experiences bottom water hypoxia in the summer. In this study, we applied a biogeochemical model that simulates dissolved oxygen concentrations on the shelf in response to varying riverine nutrient and organic carbon loads, boundary fluxes, and sediment fluxes. Five-year model simulations demonstrated that midsummer hypoxic areas were most sensitive to riverine nutrient loads and sediment oxygen demand from settled organic carbon. Hypoxic area predictions were also sensitive to nutrient and organic carbon fluxes from lateral boundaries. The predicted hypoxic area decreased with decreases in nutrient loads, but the extent of change was influenced by the method used to estimate model boundary concentrations. We demonstrated that modeling efforts to predict changes in hypoxic area on the continental shelf in relationship to changes in nutrients should include representative boundary nutrient and organic carbon concentrations and functions for estimating sediment oxygen demand that are linked to settled organic carbon derived from water-column primary production. On the basis of our model analyses using the most representative boundary concentrations, nutrient loads would need to be reduced by 69% to achieve the Gulf of Mexico Nutrient Task Force Action Plan target hypoxic area of 5000 km(2).

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Section: ■ Materials and Methodsmentioning

confidence: 99%

Modeling the Relative Importance of Nutrient and Carbon Loads, Boundary Fluxes, and Sediment Fluxes on Gulf of Mexico Hypoxia

Feist

Pauer

Melendez³

et al. 2016

Environ. Sci. Technol.

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“…These spatially explicit models enable a realistic representation of nutrient and O 2 dynamics and allow detailed analyses of the different causes of hypoxia. For the NGoM, at least four different coupled physical-biogeochemical models are currently available: the Regional Ocean Modeling System (ROMS; Fennel et al, 2011;Laurent et al, 2012), the Finite Volume Community Ocean Model (Justić & Wang, 2014), the Gulf of Mexico Dissolved Oxygen Model (Pauer et al, 2016), and the Coastal General Ecosystem Model (Lehrter et al, 2017). In the ROMS model, which includes N-and P-based nutrients, P limitation is simulated in spring and early summer, in agreement with observations (Sylvan et al, 2006), and influences the severity and distribution of hypoxia (Laurent & Fennel, 2014), but N is the ultimate limiting nutrient in the NGoM .…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quantifying the Relative Importance of Riverine and Open‐Ocean Nitrogen Sources for Hypoxia Formation in the Northern Gulf of Mexico

2019

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The Mississippi and Atchafalaya River System discharges large amounts of freshwater and nutrients into the northern Gulf of Mexico (NGoM). These lead to increased stratification and elevate primary production in the outflow region. Consequently, hypoxia (oxygen <62.5 mmol/m3), extending over an area of roughly 15,000 km2, forms every summer in bottom waters. High‐resolution models have significantly improved our understanding of the processes controlling hypoxia formation in the NGoM and have strongly implicated riverine nutrients as the dominant nutrient source. However, the relative importance of different nutrient sources (i.e., the Mississippi and Atchafalaya Rivers and offshore) has not been assessed before now. Here, we combine a high‐resolution model with an element tracing method to directly quantify the relative contributions of nitrogen from the two rivers and the open ocean to primary production and sediment oxygen consumption, which is the main oxygen sink contributing to hypoxia in the NGoM. Our results indicate that, averaged over 2001–2011, Mississippi and Atchafalaya nitrogen support 51 ± 9% and 33 ± 9% of summer sediment oxygen consumption, respectively, while open‐ocean nitrogen supports 16 ± 2%. The higher relative impact of Mississippi inputs results from longer transit times compared to those of Atchafalaya inputs. We also analyze the effect of riverine nitrogen load reductions and a larger diversion of discharge to the Atchafalaya River. These scenario simulations show that nutrient load reductions are most effective in mitigating hypoxia.

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“…An understanding of the biological, physical, and chemical processes that influence hypoxic areas is a critical concern for mitigating and preventing these negative impacts. Numerical ecosystem models are important tools that synthesize knowledge of ecosystem processes that contribute to hypoxia formation and for predicting the effects of proposed management activities or future scenarios (Scavia et al, 2004;Hagy and Murrell, 2007;Camacho et al, 2014b;Pauer et al, 2016). Unlike statistical models with more generic structures, simulation and process-based models include explicit descriptions of relevant processes that are constrained by empirical or observational data relevant to the system of interest (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…These models are often coupled with hydrodynamic grids to provide spatially-explicit representations of patterns in three dimensions (Warner et al, 2005;Dortch et al, 2007;Zhao et al, 2010;Ganju et al, 2016). Combined hydrodynamic and bio-geo-chemical models have been developed specifically to describe hypoxic conditions on the Louisiana continental shelf (LCS) in the northern Gulf of Mexico (GOM) (Fennel et al, 2013;Obenour et al, 2015;Pauer et al, 2016;Lehrter et al, 2017). This area drains a significant portion of the continental United States through the Mississippi-Atchafalaya River Basin (MARB) and is the second largest hypoxic area in the world (Rabalais et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Parameter sensitivity and identifiability for a biogeochemical model of hypoxia in the northern Gulf of Mexico

Beck

Lehrter

Lowe

et al. 2017

Ecological Modelling

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Local sensitivity analyses and identifiable parameter subsets were used to describe numerical constraints of a hypoxia model for bottom waters of the northern Gulf of Mexico. The sensitivity of state variables differed considerably with parameter changes, although most variables were responsive to changes in parameters that influenced planktonic growth rates and less sensitive to physical or chemical parameters. Variation in sensitivity had a direct correspondence with identifiability, such that only small subsets of the complete parameter set had unique effects on the model output. Selecting parameters by decreasing sensitivity demonstrated that only eight of 51 total parameters had a sufficiently unique effect on model output for accurate calibration. As a result, parameter selection heuristics were used to identify parameters for model calibration that depended on combined effects on output, relative sensitivity of each parameter, and ecological categories for the biogeochemical equations. The calibrated zero-dimensional (0-D) unit of the hypoxia model had improved fit to the observed data if sensitive phytoplankton parameters were included in an identifiable subset. Extension of results to a three-dimensional grid of the Gulf of Mexico showed that sensitive parameters for the 0-D model translated to non-trivial changes in the areal estimates of hypoxia.

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A modeling study examining the impact of nutrient boundaries on primary production on the Louisiana continental shelf

Cited by 5 publications

References 37 publications

Modeling the Relative Importance of Nutrient and Carbon Loads, Boundary Fluxes, and Sediment Fluxes on Gulf of Mexico Hypoxia

Modeling the Relative Importance of Nutrient and Carbon Loads, Boundary Fluxes, and Sediment Fluxes on Gulf of Mexico Hypoxia

Quantifying the Relative Importance of Riverine and Open‐Ocean Nitrogen Sources for Hypoxia Formation in the Northern Gulf of Mexico

Parameter sensitivity and identifiability for a biogeochemical model of hypoxia in the northern Gulf of Mexico

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