Salinisation: A major threat to water resources in the arid and semi‐arid regions of the world

Abstract

Semi-arid and arid regions (i.e. drylands with annual mean rainfall between 25 and 500 mm) cover approximately one-third of the world's land area and are inhabited by almost 400 million people. Because they are a resource in short supply, waters in drylands are under increasing human pressures, and many are threatened by rising salinities (salinisation) in particular. Rising salinities result from several causes. The salinities of many large natural salt lakes in drylands are rising as water is diverted from their inflows for irrigation and other uses. The excessive clearance of natural, deep-rooted vegetation from catchments and the discharge of saline agricultural wastewater causes the salinity of many freshwater lakes, wetlands and rivers to rise. The salinisation of some fresh waters is caused by rising saline groundwaters. And in some regions, increasing climatic aridity may be a cause of salinisation. Whatever the cause, salinisation has significant economic, social and environmental impacts. They are usually deleterious and often irreparable. Decreased biodiversity, changes in the natural character of aquatic ecosystems, and lower productivity are frequent ecological effects. In some dryland countries, salinisation is viewed as the single most important threat to water resources. However, the extent and importance of salinisation as a global threat has been greatly underestimated. Recognition of this is the first step in any attempt to manage it effectively. The aims of the present paper, therefore, are three-fold. First, it aims to define the problem and indicate its extent; second, it aims to outline the causes and effects of salinisation; third, it aims to highlight the social, economic and environmental costs and comment on management responses. An overarching aim is to draw attention to the importance of salinisation as a phenomenon of global significance to waters in drylands

Where does all the water go? Partitioning water transmission losses in a data-sparse, multi-channel and low-gradient dryland river system using modelling and remote sensing

“…Drylands cover approximately one-third of the Earth's surface and their limited water resources are under increasing pressure (Williams, 1999). Dryland regions are characterised by highly variable rainfall and episodic river flows (Tooth, 2000), often resulting in rivers with a unique geomorphological form-anabranching-which is characterised by low-gradient and multichannel river systems with large floodplains that are graded to transmit large yet infrequent and slow-moving flood pulses.…”

Arbuscular mycorrhizal symbiosis and alleviation of salinity stress

“…Consequently, a reduction in crop yields, mainly because of osmotic stress, as well as nutritional and toxic effects occurred. It is estimated that at least one third of all irrigated agricultural lands are affected to some degree by salinity (Williams, 1999). Furthermore, the increasing demands in food production constantly push agricultural fields to areas where water and soils have naturally or not high salt levels (Araus et al, 2007).…”

Influence of environmental factors on zooplankton assemblages in Bosten Lake, a large oligosaline lake in arid northwestern China

“…Waters in semi-arid and arid regions (i.e., drylands with annual mean rainfall between 25 and 500 mm) are threatened by rising salinities owing to natural, and more generically, anthropogenic processes 1 . Environmental impacts of salinization include decrease of species diversity and abundance 2 , change in the natural character of aquatic ecosystems, i.e., enhancement of clarification rate 3 , change in the relative proportions of cations and anions 4 , anoxia of bottom water 5 , elevated levels of sulphate, dissolved iron and, nitrate 6 , and reduction of water productivity 7 .…”

“…For example, the threshold salinity level functionally delimiting freshwater from brackish lake communities has been suggested to occur at 2 psu (practical salinity units) 9 . And the greatest impacts may occur when original salinities are low 1 , for the more limited halotolerance of the freshwater biota than the biota of salt lakes. Hence freshwater or oligosaline ecosystems may be much more sensitive to salinity variations, and small increases may make big difference.…”