Soil Salinity Salinity in both the rivers and on the land is one of the main and most costly results of overclearing and irrigation. Salinity is caused by changes in the delicate balance between surface water and groundwater systems. A small increase in the infiltration of water from the topsoil to the groundwater, due to rainfall or irrigation, can result in a dramatic rise in groundwater pressure and watertable levels. The trees of the open forests are now replaced by shallow-rooted crops and pastures which absorb far less water than the native trees. Those trees had been massive water pumps, sucking