Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes

Laurent, Arnaud; Fennel, Katja; Hu, Jiatang; Hetland, Robert D.

doi:10.5194/bg-9-4707-2012

Cited by 63 publications

(85 citation statements)

References 52 publications

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“…Realistic representations of phytoplankton variability in regions with strong physical and biochemical gradients, like those in the northern GoM, are challenging. Previous modeling efforts on the LouisianaTexas shelf based on Fennel's model reproduced better the mean satellite chlorophyll condition than our model (e.g., Fennel et al, 2011;Laurent et al, 2012). However, Fennel's model tends to overestimate satellite chlorophyll by a factor > 3 in the deep-ocean region during winter, which could be linked to misrepresentation of microzooplankton grazing (see Sect.…”

Section: Discussionmentioning

confidence: 55%

“…The model does not include phosphate as a limiting nutrient for phytoplankton growth. Although previous studies have indicated the existence of phosphate limitation near the MS-A deltas during May-July (Sylvan et al 2006(Sylvan et al , 2007Laurent et al, 2012;Laurent and Fennel, 2014;Fennel and Laurent, 2017), we focus here on the role of N and Si, as observational studies suggest that N and Si can modulate phytoplankton production and composition across the northern GoM (Dortch and Whitledge, 1992;Nelson and Dortch, 1996;Lohrenz et al, 1997;Rabalais et al, 2002;Zhao and Quigg, 2014).…”

Section: Model Descriptionmentioning

confidence: 99%

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Seasonal patterns in phytoplankton biomass across the northern and deep Gulf of Mexico: a numerical model study

et al. 2018

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Abstract. Biogeochemical models that simulate realistic lower-trophic-level dynamics, including the representation of main phytoplankton and zooplankton functional groups, are valuable tools for improving our understanding of natural and anthropogenic disturbances in marine ecosystems. Previous three-dimensional biogeochemical modeling studies in the northern and deep Gulf of Mexico (GoM) have used only one phytoplankton and one zooplankton type. To advance our modeling capability of the GoM ecosystem and to investigate the dominant spatial and seasonal patterns of phytoplankton biomass, we configured a 13-component biogeochemical model that explicitly represents nanophytoplankton, diatoms, micro-, and mesozooplankton. Our model outputs compare reasonably well with observed patterns in chlorophyll, primary production, and nutrients over the Louisiana-Texas shelf and deep GoM region. Our model suggests silica limitation of diatom growth in the deep GoM during winter and near the Mississippi delta during spring. Model nanophytoplankton growth is weakly nutrient limited in the Mississippi delta year-round and strongly nutrient limited in the deep GoM during summer. Our examination of primary production and net phytoplankton growth from the model indicates that the biomass losses, mainly due to zooplankton grazing, play an important role in modulating the simulated seasonal biomass patterns of nanophytoplankton and diatoms. Our analysis further shows that the dominant physical process influencing the local rate of change of model phytoplankton is horizontal advection in the northern shelf and vertical mixing in the deep GoM. This study highlights the need for an integrated analysis of biologically and physically driven biomass fluxes to better understand phytoplankton biomass phenologies in the GoM.

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Section: Discussionmentioning

confidence: 55%

Section: Model Descriptionmentioning

confidence: 99%

Seasonal patterns in phytoplankton biomass across the northern and deep Gulf of Mexico: a numerical model study

et al. 2018

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“…The original N cycle model has been expanded to include phosphate as additional nutrient (Laurent et al, 2012), dissolved oxygen and river-derived dissolved organic matter (Yu et al, 2015b). An up-to-date description of the model equations is provided in the supplemental information of Laurent et al (2017).…”

Section: Methodsmentioning

confidence: 99%

“…N is generally limiting primary production in the Gulf of Mexico; however, observations (Sylvan et al, 2006(Sylvan et al, , 2007 and models (Laurent et al, 2012;Laurent and Fennel, 2014) have shown that in spring and early summer, during the time when hypoxic conditions are established, P is limiting in the Mississippi River plume. The effect of P limitation on hypoxia in this system has been debated.…”

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confidence: 99%

N and P as ultimate and proximate limiting nutrients in the northern Gulf of Mexico: Implications for hypoxia reduction strategies

Fennel¹,

Laurent²

2017

Preprint

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Abstract. The occurrence of hypoxia in coastal oceans is a growing problem worldwide and clearly linked to anthropogenic nutrient inputs. While the need for reducing anthropogenic nutrient loads is generally accepted, it is costly and thus requires scientifically sound nutrient-reduction strategies. Issues under debate include the relative importance of nitrogen (N) and phosphorus (P), and the magnitude of reduction requirements.The largest anthropogenically induced hypoxic area in North American coastal waters (of 15,000+/-5,000 km Here we report the first systematic analysis of the effects of single and dual nutrient load reductions from a spatially explicit 10 physical-biogeochemical model for the northern Gulf of Mexico. The model has been shown previously to skillfully represent the processes important for hypoxic formation. Our analysis of an ensemble of simulations with stepwise reductions in N, P and N&P loads provides insight into the effects of both nutrients on primary production and hypoxia, and allows us to estimate what nutrient reductions would be required for single and dual nutrient reduction strategies to reach the hypoxia target. Our results show that, despite temporary P limitation, N is the ultimate limiting nutrient for primary production in this system. 15Nevertheless, a reduction in P load would reduce hypoxia because primary production in the region where density stratification is conducive to hypoxia development, but reduction in N load have a bigger effect. Our simulations show that, at present loads, the system is saturated with N, in the sense that the sensitivity of primary production and hypoxia to N load is much lower than it would be at lower N loads. We estimate that reduction of 63% +/-18% in total N load or 48% +/-21% in total N&P load are necessary to reach a hypoxic area of 5,000 km 2 , which is consistent with previous estimates from statistical regression models 20 and highly simplified mechanistic models.

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“…Omission of phosphate cycling is justified by results of earlier studies (e.g., Rabalais et al, 2002) that have shown that the primary production on the LATEX shelf is typically nitrogen-limited during the low discharge season, and that dissolved NO x : PO 4 ratios are often higher than the 16 : 1 "Redfield ratio" (Lohrenz et al, 2008;Lohrenz et al, 1997;Lohrenz et al, 1999). An understanding of the role of phosphate and how its rapid recycling affects regional marine ecosystem processes warrants more detailed study (e.g., Laurent et al, 2012 for the LATEX shelf). However, here we focus on nitrogen and will report on the role of phosphate in a future correspondence.…”

Section: Biogeochemical Modelmentioning

confidence: 99%

Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

Xue

Fennel

et al. 2013

Biogeosciences

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Abstract.A three-dimensional coupled physicalbiogeochemical model is applied to simulate and examine temporal and spatial variability of circulation and biogeochemical cycling in the Gulf of Mexico (GoM). The model is driven by realistic atmospheric forcing, open boundary conditions from a data assimilative global ocean circulation model, and observed freshwater and terrestrial nitrogen input from major rivers. A 7 yr model hindcast (2004)(2005)(2006)(2007)(2008)(2009)(2010) was performed, and validated against satellite observed sea surface height, surface chlorophyll, and in situ observations including coastal sea level, ocean temperature, salinity, and dissolved inorganic nitrogen (DIN) concentration. The model hindcast revealed clear seasonality in DIN, phytoplankton and zooplankton distributions in the GoM. An empirical orthogonal function analysis indicated a phaselocked pattern among DIN, phytoplankton and zooplankton concentrations. The GoM shelf nitrogen budget was also quantified, revealing that on an annual basis the DIN input is largely balanced by the removal through denitrification (an equivalent of ∼ 80 % of DIN input) and offshore exports to the deep ocean (an equivalent of ∼ 17 % of DIN input).

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Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes

Cited by 63 publications

References 52 publications

Seasonal patterns in phytoplankton biomass across the northern and deep Gulf of Mexico: a numerical model study

Seasonal patterns in phytoplankton biomass across the northern and deep Gulf of Mexico: a numerical model study

N and P as ultimate and proximate limiting nutrients in the northern Gulf of Mexico: Implications for hypoxia reduction strategies

Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

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