A review of water column processes influencing hypoxia in the northern Gulf of Mexico

Dagg, M.; Ammerman, James W.; Amon, Rainer M. W.; Gardner, Wayne S.; Green, Rebecca E.; Lohrenz, Steven E.

doi:10.1007/bf02841331

Cited by 111 publications

(77 citation statements)

References 86 publications

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“…3), reflecting mixing and biological processes, which is consistent with previous studies (Cai, 2003;Dagg et al, 2007). For the June 2003 dataset, maximum biological nutrient and DIC uptake were observed at salinities between 10 and 16 (Fig.…”

Section: Mixing Pattern Vs Biological Removal Intensity In Various Lsupporting

confidence: 90%

The stoichiometry of inorganic carbon and nutrient removal in the Mississippi River plume and adjacent continental shelf

et al. 2012

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Abstract. The stoichiometry of dissolved inorganic carbon (DIC) and nutrients during biological uptake is widely assumed to follow the Redfield ratios (especially the C / N ratio) in large river plume ecosystems. However, this assumption has not been systematically examined and documented, because DIC and nutrients are rarely studied simultaneously in river plume areas and interpretation of ratios can be confounded by strong river-ocean mixing as well as intense biological activity. We examined stoichiometric ratios of DIC and nutrients (NO and calculated biological removal as the difference between observed concentrations and those predicted from conservative mixing, as determined from a multi-endmember mixing model and observed salinity and total alkalinity. Despite complex physical and biogeochemical influences, relationships between DIC and nutrients were strongly dependent on salinity range and geographic location, and influenced by biological removal. Lower C / Si and N / Si ratios in one nearshore area were likely due to localized input of high Si and low NO − 3 water from adjacent wetlands or preferential removal of nitrogen in the area. When net biological uptake was separated from river-ocean mixing and corrected for preferential N removal, the stoichiometric ratio of C / N / Si was similar to the Redfield ratio, thus supporting the applicability of the Redfield-type C / N / Si ratios in river-plume biogeochemical models.

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Section: Mixing Pattern Vs Biological Removal Intensity In Various Lsupporting

confidence: 90%

The stoichiometry of inorganic carbon and nutrient removal in the Mississippi River plume and adjacent continental shelf

et al. 2012

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“…The effects of hypoxia in this dynamic, river-dominated ocean margin (RiOMar) [Bianchi et al, 2006;McKee et al, 2004] are not comparable to those found in many other traditional semienclosed estuarine systems [Dagg et al, 2007]. We propose that the following four natural and anthropogenically derived characteristics within this RiOMar are partial reasons for the aforementioned resiliency of this system under hypoxic conditions: (1) spatial/temporal variability in freshwater inputs and associated oceanic processes that affect water column stability; (2) diversity of organic matter sources; (3) organic matter diagenesis and transport in mobile muds; and (4) proximity of the Mississippi Canyon and storm events.…”

Section: River-dominated Marginscontrasting

confidence: 65%

Controlling Hypoxia on the U.S. Louisiana Shelf: Beyond the Nutrient‐Centric View

et al. 2008

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As the Earth's population continues to increase, the projected effects of contaminant loading and human encroachment on biodiversity remain unclear. One area of intense interest is coastal eutrophication and associated hypoxia events (with hypoxia defined as oxygen <2 milligrams per liter = 1.4 milliliters per liter = ˜63 micromoles per cubic decimeter). On average, the Mississippi River discharges to the northern Gulf of Mexico (GOM) 550 cubic kilometers of freshwater and approximately 60–70×109 moles of dissolved inorganic nitrogen per year [Dagg et al., 2004], which contains anthropogenic nitrogen derived primarily from agricultural fertilizer as well as effluent from animal feedlots.

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“…As in earlier studies of the Louisiana Shelf (Morse and Eldridge, 2007;Eldridge and Morse, 2008), the diagenetic model does not represent DNRA and anammox. Although DNRA can be an important contributor to the N cycle under severe hypoxia (Dale et al, 2013), there is a poor understanding of the importance of DNRA on the Louisiana Shelf due to the lack of observations (Dagg et al, 2007). High porewater sulfide concentrations near the sediment-water interface are not reported for sediments of the Louisiana Shelf (Lin and Morse, 1991;Morse and Eldridge, 2007), which tend to minimize the importance of DNRA.…”

Section: Discussionmentioning

confidence: 99%

Parameterization of biogeochemical sediment–water fluxes using in situ measurements and a diagenetic model

et al. 2016

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Abstract. Diagenetic processes are important drivers of water column biogeochemistry in coastal areas. For example, sediment oxygen consumption can be a significant contributor to oxygen depletion in hypoxic systems, and sedimentwater nutrient fluxes support primary productivity in the overlying water column. Moreover, nonlinearities develop between bottom water conditions and sediment-water fluxes due to loss of oxygen-dependent processes in the sediment as oxygen becomes depleted in bottom waters. Yet, sedimentwater fluxes of chemical species are often parameterized crudely in coupled physical-biogeochemical models, using simple linear parameterizations that are only poorly constrained by observations. Diagenetic models that represent sediment biogeochemistry are available, but rarely are coupled to water column biogeochemical models because they are computationally expensive. Here, we apply a method that efficiently parameterizes sediment-water fluxes of oxygen, nitrate and ammonium by combining in situ measurements, a diagenetic model and a parameter optimization method. As a proof of concept, we apply this method to the Louisiana Shelf where high primary production, stimulated by excessive nutrient loads from the Mississippi-Atchafalaya River system, promotes the development of hypoxic bottom waters in summer. The parameterized sediment-water fluxes represent nonlinear feedbacks between water column and sediment processes at low bottom water oxygen concentrations, which may persist for long periods (weeks to months) in hypoxic systems such as the Louisiana Shelf. This method can be applied to other systems and is particularly relevant for shallow coastal and estuarine waters where the interaction between sediment and water column is strong and hypoxia is prone to occur due to land-based nutrient loads.

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A review of water column processes influencing hypoxia in the northern Gulf of Mexico

Cited by 111 publications

References 86 publications

The stoichiometry of inorganic carbon and nutrient removal in the Mississippi River plume and adjacent continental shelf

The stoichiometry of inorganic carbon and nutrient removal in the Mississippi River plume and adjacent continental shelf

Controlling Hypoxia on the U.S. Louisiana Shelf: Beyond the Nutrient‐Centric View

Parameterization of biogeochemical sediment–water fluxes using in situ measurements and a diagenetic model

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