Spatial-temporal assessment of pollutions in Ekbatan lake using qualitative indices and statistical methods

The purpose of this study was to use water quality indices and statistical methods based on physicochemical parameters for spatial-temporal assessment of Ekbatan lake pollution. Sampling stations were selected based on systematic, non-random approach, and it was performed in 7 stations, with intervals of 30 days in 2010-2011. At first, indices model of IRWQI, NSFWQI, and TLI was prepared in GIS environment based on qualitative parameters by interpolation functions (deterministic and geostatistical methods). Results demonstrated that qualitative parameters of FC, NO₃^-, BOD₅, DO_Sat%, pH, PO₄^3- and Turb respectively with annual average quality of 13.5 very bad, 27.4 bad, 46.8, 47.2 and 48.6 moderate, 70 goodish, and 71 good using statistical and geostatistical methods-accounted for highest pollution level and created greatest impact on lake pollution status. This amount was considered as bad and eutrophication quality on the southern and east margins of the lake because of the effluent load of the rivers under high land use activities (especially residential and then agricultural) in comparison with the lake core and north (showing baddish and moderate quality status) has more pollution level than that. Also, all parameters showed a high positive correlation and significance with increased of water temperature owing to increase in pollutant land use activities and condensation of pollutants and decreased of floodrains in warm seasons, and two parameters of TDS and Turb show high significance rather than beginning floodrains in spring and autumn. Also, lake was in qualitative status of baddish 43.7, moderate 58.2, and mild eutrophication 57.2 based on IRWQI, NSFWQI, and TLI_Chl.a respectively. Further, according to IRWQI index, the quality of lake in summer was in baddish status of 35, in half of initial winter in goodish condition of 56 and spring and autumn in moderate qualitative status of 46.