Condition of pH and ionic composition of water in a macrophyte dominated reservoir (Hanna Reservoir- Isfahan Province), Iran

2/3 of the reservoir surface area was approximately covered with dense populations of Myriophyllum, Ceratophyllum and Potamogeton species. The headwaters of the reservoir were considered as hard water and had both carbonatic and non-carbonatic hardness. When they were exposed to lentic condition of the reservoir and its intensive photosynthetic activities of macrophyte communities, the bicarbonate ions were absorbed significantly and the pH of water increased to relatively serious levels and calcium carbonate precipitated as subsequontly. These processes caused a significant decrease in calcium and bicarbonate ion concentrations of the water column of the reservoir. Thus, in the headwaters, calcium and bicarbonate ions were dominated and the cationic and anionic ratios in water were in the order of Ca2 +>Mg2+>Na+ and HCO3 >C  l->CO32->SO4-2 respectively. But in the water column of the reservoir, due to above mentioned reasons, magnesium and chloride ions prevailed and ionic status order changed to Mg2+ >Ca2+>Na+, and C l->HCO3->CO32->SO42-