Mixing conservative

Loder TC, Reichard RP (1981) The dynamics of conservative mixing in estuaries. Estuar 4 64-69 Lolvendahl R (1987) Dissolved uranium in the Baltic Sea. Marine Chem 21 213-227 Maeda M, Windom H L (1982) Behavior of uranium in two estuaries of the southeastern United States. Marine Chem 11 427-436... 

The conservative mixing of two components requires linear relationships for every pair of species. We take two end-members j = a and j = fi and note the bulk system... 

A water parcel sampled from anywhere in the mixing zone should have a T-S signature that plots on the conservative mixing line established by the mixing end members. Thus, a 50-50 mixture of two adjacent water masses (or types) generates a temperature and salinity signature that is midway between that of the end members. Because of this linear relationship, the relative proportions of these end members in any admixture can be calculated from a system of two simultaneous equations ... 

In the Pacific Ocean, most of the waters at 2500 m have a prefiormed phosphate concentration intermediate between NADW and AABW. Because preformed phosphate is a conservative tracer, it can be used to estimate the proportions of NADW and AABW present in the deep zones of the ocean basins. The average deep-water preformed phosphate concentration is 1.4 (jlM. This concentration would result from an equal-volume admixture of NADW and AABW. This conservative mixing estimate is based on the assumption that the preformed phosphate concentrations of the end-member water masses have remained constant over time scales at least as long as the mixing time of the ocean. 

Caballing The process of densification in which the nonlinear equation of state of seawater causes the product of conservative mixing of two water masses to be denser than either of the two mixing end members. 

Figure 7.11 Concentrations of dissolved Ra in the mixing zone of Winyah Bay (USA), which clearly demonstrate higher Ra activities greater than the conservative mixing line. (Modified from Moore, 1992.)...

Mississippi River plume 270-330 Conservative mixing during winter but with source input during summer Benner et al. (1992)... 

Fry, B. (2002) Conservative mixing of stable isotopes across estuarine salinity gradients a conceptual framework for monitoring watershed influences on down stream fisheries production. Estuaries 25, 264—271. 

Figure 7 The variations of chloride, calcium, strontium (in mgL ), and Sr/ Sr ratios during intrusion of seawater into the coastal aquifer of Salinas Valley, California, USA. Note the linear relationships between all constituents, which indicates conservative mixing relationships between freshwater and modified seawater. These relationships suggest that base-exchange reactions occur at early stage of seawater intrusion and that Sr in exchange sites has a high Sr/ Sr ratio (source Vengosh et aL, 2002a).

Fig. 6.3 Idealized plots of estuarine mixing illustrating conservative and non-conservative mixing. Cp and Csare the concentrations of the ions in river and seawater respectively. After Burton and Liss (1976), with permission from Elsevier Science.

If the concentration of the measured component is, like salinity, controlled by simple physical mixing, the relationship will be linear (Fig. 6.3). This is called conservative behaviour and may occur with riverine concentrations higher than, or lower than, those in seawater (Fig. 6.3). By contrast, if there is addition of the component, unrelated to salinity change, the data will plot above the conservative mixing line (Fig. 6.3). Similarly, if there is removal of the component, the data will plot below the conservative mixing line (Fig. 6.3). In most cases, removal or input of a component will occur at low salinities and the data will approach the conservative line at higher salinity (Fig. 6.4). Extrapolation of such a quasiconservative line back to zero salinity can provide, by comparison with the measured zero salinity concentration, an estimate of the extent of removal (Fig. 6.4a) or release (Fig. 6.4b) of the component. 

Figure 12.5 Extent of iron aggregation as a function of salinity in the Saco River estuary, calculated as the percent loss from a conservative mixing line connecting filtrable iron concentrations of the river water and seawater end members. Open symbols are samples with T < 14°C solid symbols are samples with T > 14°C. Reprinted from Geochim. et Cos-mochim. Acta, 46, L. M. Mayer, Aggregation of colloidal iron during estuarine mixing ...

The various factor analysis methods which became widely available during the 1970s are ideally suited to the examination of conservative mixing (Klovan Imbrie, 1971). They can be used to simultaneously classify sites and identify independently varying compositional components. Dean et al. (1988 1993) apply Q-mode factor analysis to total elemental analyses of lake surface sediments, with a view to regional classification and sediment source characterization. The approach uses a varimax rotation. This is a numerical procedure that rigidly rotates the selected axes to maximize or minimize the variable scores on each axis. This helps in the interpretation of the factors as real end-members. 

In spite of the obvious merits of this approach to dealing with conservative mixing in soils and sediments, it has been little applied. 

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