Water exchange, horizontal/vertical

Summarizing the estimates made before, temporal changes on the monthly scale encountered in a selected water column are likely to be attributed to horizontal advection in the near-bottom water but to vertical exchange in the surface water. 

In the epilimnion/hypolimnion two-box model the vertical concentration profile of a chemical adopts the shape of two zones with constant values separated by a thin zone with an abrupt concentration gradient. Often vertical profiles in lakes and oceans exhibit a smoother and more complex structure (see, e.g., Figs. 19.1a and 19.2). Obviously, the two-box model can be refined by separating the water body into three or more horizontal layers which are connected by vertical exchange rates. 

Organochlorosilanes can be also rectified in horizontal rectification towers (Fig. 6). These towers are peculiar in that they use rotating impellers 2, which spray liquid through vapour (in vertical towers, on the contrary, pressurised vapour passes through liquid) and thus mix liquid and vapour. Besides, horizontal towers use new constructions of water drain devices and breaker blades. Due to the impellers, horizontal rectification towers are more convenient to operate than vertical ones. Horizontal towers do not have to be veiy long, because there is no liquid loss in them, like in vertical apparatuses. Moreover, horizontal towers allow for vacuum rectification with veiy slight pressure differences, because there is no necessity of an increased pressure for mass exchange. 

Budget methods. Vertical exchange rates and turbulent diffusivities Kz can be calculated from the heat balance or the mass balance of tracers for which transformation rates are known. Assuming horizontal homogeneity, the temporal change of tracer mass below a given depth z must be the sum of the net vertical mass flux through the cross-section at z and all sources and sinks of tracer mass below z. In the case of conservative tracers sources and sinks below z must be mass fluxes across the sediment-water interface. In the case of H, radioactive decay is an additional sink. In the case of He, tritium decay represents a source. If the increase of mass due to all sources and sinks, Sm, is known, the net mass flux can be calculated ... 

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