Perhaps the greatest threat to saline lakes is anthropogenic or secondary salinization - in other words increased lake salinity as a result of human activity (industry, agriculture, construction) in the lake basin (Figure 6). In fact, W.D. Williams has stated that 'in some countries, anthropogenic salinization represents the most important threat to water resources.' For example, the disruption of the hydrological cycle by agriculture or diversion or damming of lake inflows can lead to freshwaters becoming saline and saline waters becoming more saline. On the Murray River flood plain in Australia, for example, agricultural clearing and land irrigation have caused the saline aquifer to rise. Concomitant salinization of flood-plain wetlands has led to the disappearance of wetland macrophytes and riparian trees. Their disappearance is testament to the fact that small increases in salinity can have a large effect on biota due to the narrow salinity tolerance range for freshwater organisms. In Australia, it is estimated that anthropogenic salini-zation costs in excess of $50 million US annually.
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