**7. Salinity changes**

Water salinity is generally defined as the total content of the salts dissolved in water. In the case of storage reservoirs, usually the contents of chlorides, sulphates, potassium and sodium ions are determined in water. High salinity can be harmful to the environment and it should be monitored.

### **7.1. Chlorides and sulphates**

The occurrence of chloride ions is common in the environment, including water. Their content in natural non-polluted water ranges from trace level to several hundred mg dm−3. They are also present in vegetation and in animals. The presence of chlorides in water is responsible for the increased rate of corrosion. Chlorides are also harmful to fresh water vegetation [7].

In the hydrological years 2004–2006, the monthly average concentration of chlorides in the reservoir was in the range from 13.88 to 53.00 mg dm−3 (**Figure 10**). The concentration distribution was characterized by relatively low dispersion. The highest concentrations were found in early spring during snow cover melting. In winter, snow from roads was discharged into the neighbourhood of the reservoir and in the valley of the Mała Panew river. Generally, snow from the roads contains increased amounts of chlorides used in winter road maintenance. Chlorides with water from snow melting could reach the reservoir.

**Figure 10.** Changes in the average monthly chloride concentrations in the waters of the Turawa reservoir in the hydrological years 2004–2006.

The sulphates occur in natural waters in a wide range of concentrations. They are present at especially high concentrations, even up to 6000 mg dm−3, in mine waters. The Turawa reservoir is surrounded by coniferous forests which assimilate larger amounts of SO2 than deciduous forests. Sulphur in needle trees is in the form of sulphate ions, which can be leached out from fallen needles. However, anthropogenic factors had the most critical influence on the content of sulphates in the reservoir water. In the period studied, the average monthly concentration of sulphates in the reservoir water ranged from 28.9 to 76.7 mg dm−3 (**Figure 11**); the average for all the studied period was 52.2 mg dm−3.

**Figure 11.** Changes in the average monthly sulphate concentrations in the waters of the Turawa reservoir in the hydrological years 2004–2006 (own elaboration).

The highest sulphate concentrations were found in winter due to decay of organic matter rich in sulphur compounds. In summer time, sulphate concentration dropped because living organisms were taking in sulphates and because, in anaerobic conditions in the benthic layer, they were reduced to hydrogen sulphide.
