Evaluation of Isotope Hydrology in Wetlands in North of Iran and Grouping of them by Principal Component Analysis

In order to assess the isotope hydrology in different water reservoirs in the north of Iran and to group them in relation to different chemical and physiographical parameters on catchment scale, an extensive study was conducted during 2010 to 2011 in 30 different wetlands. The samples were collected at three different seasons and analyzed for chemical and isotopic components. The isotopic data show that the selected wetlands cover a wide range of isotopic signatures, affected by climate, hydrology and local seasonal parameters. In most wetlands, the isotopic signatures in winter were lower than these in other seasons. The amount of deuterium excess was decreased from winter to spring by 12.86‰ to 0.83‰. These downward trends were continued during the spring to summer by 0.83‰ to -2.89 ‰. The results of principal components analysis (PCA) indicate that there are eight significant justifiable components with eigenvalue more than one which could describe differences between ponds (by 72%) in catchment scale in our experiment. The data showed that there is a significant decrease in d-excess during spring and summer in ponds 20, 21, 22, 24, 25 and 26 indicating the presence of light isotopes in these ponds. Physical separation of 18O and 2H by water molecules and prevalence of 2H in the movements led to increment of d-excess in most wetlands. This has led to d-excess of pond 12 even greater in summer than in winter. This could be an acceptable reason for ponds 25 and 26 (Siyahkal county) with the highest amount of d-excess and the lowest amounts of 18O and 2H. It seems that light water pumped from groundwater wells with minor source of salt (originated from sea deep percolation) into the ponds, may be another reason for the significant decrease in the heavy isotopes of water (18O and 2H) as for the ponds 2, 12, 14 and 25 from spring to summer.