4 Hydrological Systems

Hydrologically, a chemically closed system is one in which both solutes and water enter but only water can leave because the only outflow is evaporation which leaves solutes behind. There is no solute output thus solutes increase over time. In contrast, an open system is one that solutes and water both enter and leave so solutes do not accumulate. In reality most systems are “leaky.” In a “leaky” system selected solutes escape along with the water outflow (Figure 9).

Figure 9 – Conceptual illustration of chemically open, closed and leaky groundwater systems.

This “leaky” condition changes the amount and type of mineral deposits as well as the solute ratios in the water (Figure 10). Closed and partly open “leaky” systems are discussed in Section 4.1 and 4.2.

Figure 10 – Illustration of the contrast in mineral development between a closed basin and a “leaky” basin. The type of minerals deposited and the relative amount of individual minerals are different.