A Novel Modeling Approach to Quantify the Influence of Nitrogen Inputs on the Oxygen Dynamics of the North Sea

Große, Fabian; Kreus, Markus; Lenhart, Hermann; Pätsch, Johannes; Pohlmann, Thomas

doi:10.3389/fmars.2017.00383

Cited by 25 publications

(51 citation statements)

References 92 publications

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“…The governing equation for the rate of change of a specific source fraction reads similar to equation but with the addition of a term for biogeochemical sources and sinks. We apply the approach described by Große et al ():

\frac{\partial C_{X}^{i}}{\partial t} = \nabla \cdot ((), \overset{D}{true} \nabla C_{X}) \cdot \frac{C_{X}^{i}}{C_{X}} - \nabla \cdot ((), \overset{v}{true} C_{X}) \cdot \frac{C_{X}^{i}}{C_{X}} + R_{C_{X}} \cdot \frac{C_{X_{con}}^{i}}{C_{X_{con}}},

…”

Section: Methodsmentioning

confidence: 99%

“…For this purpose, the element tracing software (ETRAC) by Große et al () was adapted to ROMS. It requires model output for all N cycle sources and sinks (i.e., all physical and biogeochemical processes) to fulfill the following criterion for all state variables X :

V ((), t + ∆ t) \cdot C_{X} ((), t + ∆ t) - V ((), t) \cdot C_{X} ((), t) = \sum_{j = 1}^{N} P_{X, j} ((), ∆ t) .

…”

Section: Methodsmentioning

confidence: 99%

“…The relative contribution of the different nutrient sources to biogeochemical fluxes can be diagnosed with the help of an active element tracing technique described by Ménesguen et al (2006) and Große et al (2017). Here we apply this technique to the physical-biogeochemical NGoM model described in Fennel et al (2011Fennel et al ( , 2013 and Laurent et al (2012).…”

Section: Introductionmentioning

confidence: 99%

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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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\frac{\partial C_{X}^{i}}{\partial t} = \nabla \cdot ((), \overset{D}{true} \nabla C_{X}) \cdot \frac{C_{X}^{i}}{C_{X}} - \nabla \cdot ((), \overset{v}{true} C_{X}) \cdot \frac{C_{X}^{i}}{C_{X}} + R_{C_{X}} \cdot \frac{C_{X_{con}}^{i}}{C_{X_{con}}},

…”

Section: Methodsmentioning

confidence: 99%

V ((), t + ∆ t) \cdot C_{X} ((), t + ∆ t) - V ((), t) \cdot C_{X} ((), t) = \sum_{j = 1}^{N} P_{X, j} ((), ∆ t) .

…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…This impact will be especially strong in near-shore waters and coastal habitats, near to the terrestrial point sources of nutrients. Outside of the highly productive coastal zone, most primary production on the NWES is thought to be driven by oceanic nutrient input Große et al, 2017;Ruiz-Castillo et al, 2018). While most estuarine and coastal waters are net sources of CO 2 to the atmosphere (Borges et al, 2005), high inorganic nutrient inputs can lead to partial inhibition of these emissions or even to coastal waters being a net sink of atmospheric CO 2 (Kuwae et al, 2016).…”

Section: Riverine Nutrient Inputsmentioning

confidence: 99%

Carbon on the Northwest European Shelf: Contemporary Budget and Future Influences

et al. 2020

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A carbon budget for the northwest European continental shelf seas (NWES) was synthesized using available estimates for coastal, pelagic and benthic carbon stocks and flows. Key uncertainties were identified and the effect of future impacts on the carbon budget were assessed. The water of the shelf seas contains between 210 and 230 Tmol of carbon and absorbs between 1.3 and 3.3 Tmol from the atmosphere annually. Offshelf transport and burial in the sediments account for 60-100 and 0-40% of carbon outputs from the NWES, respectively. Both of these fluxes remain poorly constrained by observations and resolving their magnitudes and relative importance is a key research priority. Pelagic and benthic carbon stocks are dominated by inorganic carbon. Shelf sediments contain the largest stock of carbon, with between 520 and 1600 Tmol stored in the top 0.1 m of the sea bed. Coastal habitats such as salt marshes and mud flats contain large amounts of carbon per unit area but their total carbon stocks are small compared to pelagic and benthic stocks due to their smaller spatial extent. The large pelagic stock of carbon will continue to increase due to the rising concentration of atmospheric CO 2 , with associated pH decrease. Pelagic carbon stocks and flows are also likely to be significantly affected by increasing acidity and temperature, and circulation changes but the net impact is uncertain. Benthic carbon stocks will be affected by increasing temperature and acidity, and decreasing oxygen concentrations, although the net impact of these interrelated changes on carbon stocks is uncertain and a major knowledge gap. The impact of bottom trawling on benthic carbon stocks Frontiers in Marine Science | www.frontiersin.org 1 March 2020 | Volume 7 | Article 143Legge et al.Carbon on the Northwest European Shelf is unique amongst the impacts we consider in that it is widespread and also directly manageable, although its net effect on the carbon budget is uncertain. Coastal habitats are vulnerable to sea level rise and are strongly impacted by management decisions. Local, national and regional actions have the potential to protect or enhance carbon storage, but ultimately global governance, via controls on emissions, has the greatest potential to influence the long-term fate of carbon stocks in the northwestern European continental shelf.

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“…By combining a high-resolution biogeochemical model with this active element tracing method expanded for the quantification of the contributions to O 2 processes (Große et al, 2017(Große et al, , 2019, we provide such an analysis here. We apply the element tracing method to an implementation of the Regional Ocean Modeling System (ROMS; Fennel et al, 2006;Haidvogel et al, 45 2008) configured for the ECS (Zhang et al, same issue).…”

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confidence: 99%

Quantifying the contributions of riverine vs. oceanic nitrogen to hypoxia in the East China Sea

Große¹,

Fennel²,

Zhang³

et al. 2019

Preprint

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In the East China Sea, hypoxia (oxygen ≤ 62.5 mmol m −3 ) is frequently observed off the Changjiang (or Yangtze) River estuary covering up to about 15,000 km 2 . The Changjiang River is a major contributor to hypoxia formation because it discharges large amounts of freshwater and nutrients into the region. However, modelling and observational studies have suggested that intrusions of nutrient-rich oceanic water from the Kuroshio Current also contribute to hypoxia formation. The relative contributions of riverine versus oceanic nutrient sources to hypoxia have not been estimated before. Here, we combine 5 a three-dimensional, physical-biogeochemical model with an element tracing method to quantify the relative contributions of nitrogen from different riverine and oceanic sources to hypoxia formation during 2008-2013. Our results suggest that the hypoxic region north of 30 • N is dominated by Changjiang River inputs, with its nitrogen loads supporting 74% of oxygen consumption. South of 30 • N, oceanic nitrogen sources become more important supporting 39% of oxygen consumption during the hypoxic season, but the Changjiang River remains the main control of hypoxia formation also in this region. Model scenarios 10 with reduced Changjiang River nitrogen loads and reduced open-ocean oxygen levels suggest that nitrogen load reductions can significantly reduce hypoxia in the East China Sea and counteract a potential future decline in oxygen supply from the open ocean into the region.

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A Novel Modeling Approach to Quantify the Influence of Nitrogen Inputs on the Oxygen Dynamics of the North Sea

Cited by 25 publications

References 92 publications

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

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

Carbon on the Northwest European Shelf: Contemporary Budget and Future Influences

Quantifying the contributions of riverine vs. oceanic nitrogen to hypoxia in the East China Sea

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