Physicochemical features of Wadi Al-Arab Dam (reservoir), Jordan

Variations in physical and chemical conditions were investigated at Wadi Al-Arab Dam Reservoir (Jordan). Mean surface water temperature was 22.5°C and two distinctive temperature layers, epilimnion (down to 15 m, mean temperature 28.6°C) and hypolimnion (down to 35 m, mean temperature 21.1°C) were recognized in May. Minimum water transparency was recorded at 32 cm in July and maximum at 135 cm in August. The mean surface pH (8.0) and salinity (1.54 mg l^-1) showed no pattern of variation, with pH values of 9.31-8.1 and 5.1-3.1 recorded between February and July at 0-15 m and 15-35 m, respectively; and higher values of salinity (1.88 mg l^-1 and 1.84 mg l^-1) in the wet season. Electrical conductivity values ranged between 912 and 1257 μS cm^-1, with the highest values in summer. Records at station I and II showed a mean total alkalinity of 541.04 mg l^-1 CaCO₃ and dissolved oxygen (DO) levels of 6.2-8.9 mg l^-1 with the observation of the highest (8.0 mg l^-1) and lowest (4.0 mg l^-1) DO values in April at the surface and 15 m, respectively. In May, DO values dropped from 7.31 mg l^-1 in the upper layer to 3.85 mg l^-1 in the deepest layer. Nutrients as nitrate revealed minimum (0.7 mg l^-1 N-NO₃) and maximum (30.4 mg l^-1 N-NO₃) concentrations at the surface in station I and II, respectively. Levels of P-PO₄ were also high at stations I and II (0.73 mg l^-1 PO₄ and 1.02 mg l^-1 PO₄) in May and June, respectively. However, the minimum value (0.14-0.16 mg l^-1 PO₄) was recorded in October at both stations. Disolved reactive silica (DRS) levels showed low values of 2.55-11.46 mg l^-1 (station I in June) and 2.33-7.60 mg l^-1 (station II in May and December), respectively.