Environmental Engineering Reference
In-Depth Information
unmanageable proportions. The reliance on natural replenished fertilizer died out, result-
ing in an unsustainable open system as illustrated in Figure 15.7.
Today, with the lakes and ponds disappearing, the depths to which groundwater is
extracted is in excess of 500 m. Groundwater recharge cannot be relied on through lake
desilting alone, as the rate of groundwater withdrawal is so high that it cannot be replen-
ished by any natural means. Furthermore, with increasing depth, the power required to
draw the water increases, resulting in an ineffective use of conventional coal/petroleum-
based energy. And the biggest problem that has arisen out of this deep groundwater is
that it is replete with dissolved heavy metals and salts, such as sulfate, arsenic, luoride,
and iron, which result in severe soil pollution and require energy-intensive treatment.
Needless to say, an open system consequently causes other closed-loop systems to open
up, further exasperating the complexity of problems (Figure 15.8) facing modern society.
Farming
Clouds
Rain
Subsidies
Chemical fertilizer
Mining
(phosphates)
Hydrocarbons
(nitrates...)
Unsustainable
FIGURE 15.7
Farming cycle of today.
FIGURE 15.8
Effect of opening up of the cycle. It has become unsustainable.
