The Dynamics of Conservative Mixing in Estuaries

Loder, Theodore C.; Reichard, Ronnal P.

doi:10.2307/1351543

Cited by 144 publications

(57 citation statements)

References 11 publications

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“…Mixing curves are a commonly used approach for interpreting net source/ sink dynamics of estuarine constituents (for examples, see Officer 1979;Loder and Reichard 1981;Kaul and Froelich 1984). When observed values fall on the linear mixing curve, it is generally interpreted that the constituent of interest mixes conservatively with respect to the system's residence time.…”

Section: Methodsmentioning

confidence: 99%

“…The main problem is that the constituent being examined is assumed to be in steady state with respect to freshwater residence time. Because mixing curves are generated from concentrations at the freshwater and mouth stations, sudden large variations (i.e., non-steady state behavior) in endmember concentrations can affect the slope of a mixing curve (Loder and Reichard 1981), making a parameter appear nonconservative when in fact it is conservative. In the York River estuary, DIC at the freshwater end-member (C O , in Table 2) varied seasonally; freshwater DIC concentrations decreased during high flow periods in the winter and spring months.…”

Section: Methodsmentioning

confidence: 99%

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Atmospheric CO₂ evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary

Raymond

Bauer

Cole

2000

Limnology & Oceanography

266

182

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Direct measurements of the partial pressure of CO 2 (pCO 2 ) and dissolved inorganic carbon (DIC) were made over a 2-yr period in surface waters of the York River estuary in Virginia. The pCO 2 in surface waters exceeded that in the overlying atmosphere, indicating that the estuary was a net source of CO 2 to the atmosphere at most times and locations. Salinity-based DIC mixing curves indicate there was also an internal source of both DIC and alkalinity, implying net alkalinity generation within the estuary. The DIC and alkalinity source displayed seasonal patterns similar to that of pCO 2 and were reproducible over a 2-yr study period.We propose that the source of inorganic carbon necessary for both the sustained CO 2 evasion to the atmosphere and the advective export of DIC is respiration in excess of primary production (e.g., net heterotrophy). The rates of CO 2 evasion and DIC export were estimated to provide an annual rate of net heterotrophy of ϳ100 g C m Ϫ2 yrϪ1 . Approximately 40% of this excess inorganic carbon production was exported as DIC to the coastal ocean, whereas 60% was lost as CO 2 evasion to the atmosphere. The alkalinity generation needed to sustain the export of inorganic carbon, as HCO 3 Ϫ , is most likely provided by net sulfate reduction in sediments. Accumulation of sulfide in the sediments of a representative site directly adjacent to the York River estuary is sufficient to account for the net export of alkalinity. The seasonality of net heterotrophy causes large variations in annual CO 2 and DIC concentrations, and it stresses the need for comprehensive temporal data sets when reporting annual rates of CO 2 evasion, DIC advection, and net heterotrophy.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Atmospheric CO₂ evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary

Raymond

Bauer

Cole

2000

Limnology & Oceanography

266

182

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“…Therefore the question is worth asking, what do we learn about mixing and biogeochemical reactions from the distribution of S and O 2 in the Black Sea? It is worth recalling in this context that in estuarine physics (bearing in mind that the Black Sea can be considered as a big estuary), mixing plots, in which a dissolved constituent is plotted against salinity, are commonly used to interpret conservative and non-conservative processes (Liss, 1976;Loder and Reichard, 1981). A bend in the mixing curve is indicative of the reactive or nonconservative nature of tracers.…”

Section: Diapycnic and Isopycnic Mixing -General Considerations And Dmentioning

confidence: 99%

Mixing in the Black Sea detected from the temporal and spatial variability of oxygen and sulfide – Argo float observations and numerical modelling

et al. 2014

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Abstract. The temporal and spatial variability of the upper ocean hydrochemistry in the Black Sea is analysed using data originating from profiling floats with oxygen sensors and carried out with a coupled three-dimensional circulationbiogeochemical model including 24 biochemical state variables. Major focus is on the dynamics of suboxic zone which is the interface separating oxygenated and anoxic waters. The scatter of oxygen data seen when plotted in density coordinates is larger than those for temperature, salinity and passive tracers. This scatter is indicative of vigorous biogeochemical reactions in the suboxic zone, which acts as a boundary layer or internal sink for oxygen. This internal sink affects the mixing patterns of oxygen compared to the ones of conservative tracers. Two different regimes of ventilation of pycnocline were clearly identified: a gyre-dominated (cyclonic) regime in winter and a coastal boundary layer (anticyclonic eddy)-dominated regime in summer. These contrasting states are characterized by very different pathways of oxygen intrusions along the isopycnals and vertical oxygen conveyor belt organized in multiple-layered cells formed in each gyre. The contribution of the three-dimensional modelling to the understanding of the Black Sea hydro-chemistry, and in particular the coast-to-open-sea mixing, is also demonstrated. Evidence is given that the formation of oxic waters and of cold intermediate waters, although triggered by the same physical process, each follow a different evolution. The difference in the depths of the temperature minimum and the oxygen maximum indicates that the variability of oxygen is not only just a response to physical forcing and changes in the surface conditions, but undergoes its own evolution.

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“…The weaknesses of the former three modelling approaches have already been comprehensively documented in the literature (Officer and Lynch, 1981;Loder and Reichard, 1981;Regnier et al, 1998;Regnier and O'Kane, 2004). Yet, despite obvious flaws in these methods, they are still used by international agencies and regulatory authorities, in particular in the framework of the LOICZ program.…”

Section: Introductionmentioning

confidence: 99%

Reactive-transport modelling of C, N, and O2 in a river–estuarine–coastal zone system: Application to the Scheldt estuary

et al. 2007

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A fully coupled, two-dimensional hydrodynamic and reactive-transport model of C, N, O 2 and Si along a river-estuarinecoastal zone system is presented. It is applied to the Scheldt continuum, a macrotidal environment strongly affected by anthropogenic perturbations. The model extends from the upper tidal river and its tributaries to the southern Bight of the North Sea. Five dynamically linked nested grids are used, with a spatial resolution progressively increasing from 33 m to 2.7 km. The biogeochemical reaction network consists of aerobic degradation, nitrification, denitrification, phytoplankton growth and mortality, as well as reaeration. Diagnostic simulations of a typical summer situation in the early 1990s are compared to field data taken from the OMES database (>300 samples per variable). Results demonstrate that the process rates in the tidal river are very high and far larger than in the saline estuary, with maximum nitrification rates in the water column up to 70 mM N day − 1 , and maximum aerobic respiration and denitrification up to 70 and 40 mM C day − 1 , respectively. Phytoplankton production is about one order of magnitude lower, a result which confirms the dominance of heterotrophic processes in this system. The influence of secondary and tertiary wastewater treatment in the catchment is then assessed. Results show a significant decrease of organic matter and ammonium concentrations above Antwerp, which in turn leads to a partial restoration of oxygen levels. The model also predicts a reduction of denitrification rates, which locally results in a 4-fold increase of the nitrate concentration. Mass budgets for carbon, nitrogen and oxygen are established for the saline estuary (km 0 to 100) and for the tidal river network (km 100 to 160). Three scenarios, corresponding to the situation in the early 1990s, the years 2000 and the situation expected in 2010 are considered. They show that the tidal river and the estuary contribute almost equally to the overall biogeochemical cycling of these elements, despite the very different water volumes involved. For the simulated periods, the large decrease in nitrogen input (> 55%) expected between 1990 and 2010 will not lead to a significant decrease of N export to the coastal zone during the summer period.

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The Dynamics of Conservative Mixing in Estuaries

Cited by 144 publications

References 11 publications

Atmospheric CO₂ evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary

Atmospheric CO₂ evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary

Mixing in the Black Sea detected from the temporal and spatial variability of oxygen and sulfide – Argo float observations and numerical modelling

Reactive-transport modelling of C, N, and O2 in a river–estuarine–coastal zone system: Application to the Scheldt estuary

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The Dynamics of Conservative Mixing in Estuaries

Cited by 144 publications

References 11 publications

Atmospheric CO2 evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary

Atmospheric CO2 evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary

Mixing in the Black Sea detected from the temporal and spatial variability of oxygen and sulfide – Argo float observations and numerical modelling

Reactive-transport modelling of C, N, and O2 in a river–estuarine–coastal zone system: Application to the Scheldt estuary

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Atmospheric CO₂ evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary

Atmospheric CO₂ evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary