Indicators in the study sites

Table of Contents

1. Compilers and contributors
2. Introduction
3. Climate indicators
4. Water indicators
   1. Water quality
   2. Water quantity
   3. Ground water exploitation
   4. Water consumption/water demands
5. Soil indicators
6. Vegetation indicators
7. Water runoff indicators
8. Forest fires indicators
9. Agriculture indicators
10. Cultivation indicators
11. Animal husbandry indicators
12. Land management indicators
13. Land use indicators
14. Water use indicators
15. Tourism indicators
16. Human characteristics indicators
17. Institutional indicators
18. Conclusions
19. References

Water quality

The criteria for good water quality for irrigation in agriculture are: low salinity and low ratio of Na⁺ to Ca²⁺ Mg²⁺_. The index usually used to characterize the quality of irrigation water with respect to its influence on the exchangeable sodium percentage (soil sodification) is the sodium adsorption ratio (SAR) which is defined as follows:

SAR = [Na⁺] / {([Ca²⁺] + [Mg²⁺])/2** (1/2).

This is the ratio of the sodium ion (Na⁺) concentration to the square root of the average concentration of the divalent calcium (Ca²⁺) and magnesium (Mg²⁺) ions. One main reason of increasing amounts of salts in aquifers is sea-water intrusion due to over-exploitation resulting from increasing water demands for multiple uses. The use of poor quality water for irrigation and under certain soil and climatic conditions leads to soil salinization (Fig. 10). Increasing salt levels in the top soil layers can affect plant growth and productivity. High concentrations of various salts (e.g., sodium chloride, magnesium and calcium sulphates and bicarbonates) affect plants growth both directly by their toxicity and indirectly by increasing osmotic potential and lowering root water uptake. In dry climates continuous salt accumulation could lead to desertification, while in humid or subhumid climates moderate or severe salinization may occur periodically. Electrical conductivity of water has been used as a handy measurement for the purpose of this project. The following classes of electrical conductivity (EC) in μS have been defined: (a) EC<400 μS, (b) 400-800 μS, (c) 800-1500 μS, and (d) >1500 μS.

Fig. 10. Salt affected areas due to poor quality of ground water causing soil salinization resulting from high rates of evaporation (Botswana, left) and irrigation with high concentration of salts (Spain, right)

As Table 2 shows, water quality data used for irrigation have been collected in 361 field sites, corresponding to 5 study sites. High quality of irrigation water (electrical conductivity <400 μS) has been found in 46.8% of the study field sites located mainly in Novij Saratov-Russia and partially in Crete-Greece (Fig. 11). Low to very low quality of irrigation water (800-1500, >1500 ) has been recorded in 25.8% and 18.3% of the study field sites, respectively. Such low water quality has been measured in some field sites of Crete-Greece, Djanybek-Russia, Boteti Area-Botswana, and in Nestos Basin Maggana-Greece. Moderate quality of irrigation water (electrical conductivity 400-800 μS) has been found in 9.1% of the study field sites located in some areas of Crete-Greece and in Boteti Area-Botswana.

Fig. 11. Distribution of irrigation water quality classes prevailing in the study field sites