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Fixed net negative charge Mobile layer of

(particle surface) cations in solution

Electrical double layer

Fig. 6.2 Electrical double layer, comprising a fixed layer of negative charge on the particle and a mobile ionic layer in solution. The latter is caused because positive ions are attracted to the particle surface. Note that with increasing distance from the particle surface the solution approaches electrical neutrality. After Raiswell et al. (1980).

These reactions can significantly affect fluxes of riverine material to the oceans and therefore must be quantified in order to understand global element cycling.

6.2.2 Mixing processes in estuaries

Water flow in estuaries is not unidirectional; it is subject to the reversing flows of tides. There is therefore no constant relationship between a fixed geographic point and water properties (e.g. calcium ion (Ca2+) concentration). For this reason, data collected in estuaries are usually compared with salinity (Box 6.1) rather than location. The underlying assumption is that salinity in an estuary is simply the result of physical mixing and not of chemical changes. If the estuary has just one river entering it and no other inputs, the behaviour of any component can be assessed by plotting its concentration against salinity.

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