UNUSUAL GEOHYDROCHEMICAL PROPERTIES OF GOLGIR SULFUR SPRINGS RESULTED IN MICROBIOECOLOGICAL DEVIATIONS IN TEMBI RIVER

The salinity and unusual hydrochemistry of Tembi Riveris mainly related to the ground waters that stream in theGachsaran formation, the gypsum and evaporite basedcap rock of Asmari oil reservoir. There are seven sulfur andsulfide springs at Golgir region that introduce in to theTembi River and result in a detectable hydrochemical andmicrobioecological changes as our results showed. Also,XRF analysis of the sediments of the springs confirmedthe hydro geochemistry results. Most probable numbercounting of dissimilatory sulfate reducing, dissimilatorynitrate reducing and oxidative sulfur bacteria on adefined NaCl concentration gradient showed that thereis a very different microbial community in sediment andwater samples of the upstream and downstream of theGolgir springs introduction point. Such a difference ishighly related to the hydro geochemistry of the Golgirsprings and of course the local shallowness of Asmari oilreservoir at this region that caused natural oil seepagesinto the ground water in Gachsaran formation. Suchseepages are very common in Gachsaran formationas geographical studies showed. H2S that is producedmainly by microbial souring is the main cause of microbialmetabolism deviation to the sulfur based reductive andoxidative reactions in Golgir springs. Due to the gypsumdissolution the ground water receives concentrations ofsulfate (0.09-0.1 M). Moreover, seepage of Asmari oilreservoir resulted in the hydrocarbon contamination andreductive nature of the ground water. Sulfate reducingbacteria are enriched in the ground water and also in thevicinity of Asmari oil reservoir and their sulfate reductionresulted in H2S production. High H2S concentrationresulted in Tembi water toxification and the attenuationof O2 and NO3- based respiration and also precipitationof metal based sulfides. Such specific microbioecologicalproperties together with a long salinity gradient (10-261g/L NaCl) introduced the Tembi River as a specificecosystem for biodiversity and geomicrobiology studies.