بررسی هیدروژئوشیمی، تعیین منشا و نحوه تکامل شورابه دریاچه حوض سلطان قم

مطالعه رسوبات و شورابه پلایا از جنبه های اقتصادی با توجه به وجود ذخایر تبخیری و از نظر اثرات آن بر اکولوژی و محیط زیست و آبهای منطقه حائز اهمیت خاص می باشد. سطح آب دریاچه حوض سلطان با گستره آبگیر حدود 195 کیلومترمربع متاثر از حجم آبهای وارده به آن اعم از آبهای زیرزمینی، رودهای فصلی و بارندگی می باشد. به منظور مطالعه هیدروژئوشیمی شورابه، در این پلایا، تعداد 25 نمونه شورابه از بخش های مختلف دریاچه برداشت شد. پارامترهای فیزیکوشیمیایی در محل اندازه گیری و آنالیز شیمیایی شورابه ها انجام شد. همچنین، برای مطالعه رسوب شناسی، کانی شناسی و تعیین شوری، از محل برداشت شورابه، 100 نمونه رسوب، بوسیله اوگر دستی تا عمق بیشینه 2 متر برداشته شد. با انجام آزمایشات ژئوشیمیایی، ترکیب یونی شورابه ها و با آنالیز کانی شناسی رسوبات، نوع کانی های موجود در رسوبات مشخص گردید. ترتیب فراوانی کاتیون های موجود در شورابه به ترتیب شامل سدیم، منیزیم، کلسیم و پتاسیم و آنیونها شامل کلر، سولفات و بیکربنات می باشد. کانی های تبخیری موجود در رسوبات را کلسیت، ژیپس، هالیت، کارنالیت، هگزاهیدریت، تناردیت و باسانیت تشکیل می دهند. بررسی هیدروژئوشیمی آبهای ورودی بیانگر این است که نسبت مولی یون ها از نوع hco3 < ca + mg بوده و در نمودار تکاملی ژئوشیمیایی شورابه ها، مسیر ژئوشیمیایی (ii) را طی نموده و پس از جدایش کانی های مختلف، تیپ شورابه دریاچه naca(mg)cl می گردد که قابل مقایسه با دریاچه مهارلو، دریاچه نمک بریستول و دریاچه بزرگ نمک آمریکا است.

Investigation of hydrogeochemistry and brine evolution and sources of Hoz-e-soltan Lake, Qom

IntroductionThe study of sediments and brine of playa, from economic aspects, has special significance with respect on evaporate deposits and its effect on ecology, environment and regional water. Examinations of sedimentologic and mineralogic characteristics of the closedbasin cores due to the very high susceptibility to precipitation and evaporation balance are beneficial for determination and evolution of late Quaternary sedimentary specification. HozeSoltan Lake with a 195km2 catchment area, 2550 cm depth, located at 35 km of north of Qom, in Central Part of Iran. It is sited between 34 ordm;56 acute; and 35 ordm;31 acute; north and 50 ordm;53 acute; and 51 ordm;20 acute; east at westernnorth of HozeMasileh. It is surrounded by AliAbad and KushkeNosrat mountains in north and northeast, Manzarieh and Chahar mountains in west and MohammadAbad and Badamcheh mountains in south and southeast. This Lake is influenced by the volume of input water including groundwater, intermittent streams and precipitation.Materials and MethodsIn order to study hydrogeochemistry of brine in the playa, 25 samples of brine were taken from different parts of the Lake. Physicchemical parameters were measured in the site and chemical analysis of brines was performed. Also, to study sedimentology and mineralogy and to determine salinity, 100 sediment samples were obtained up to 2 m depth by manual auger. By implementing geochemical experiments, ionic compositions of brines were recognized and by mineralogical analysis of sediments, types of minerals which occurred in deposits were determined. Samples were collected in good quality polyethylene bottles of oneliter capacity. Each sample was divided into two separate samples before being sent to the laboratory to enhance the accuracy of the results.At the time of sampling, the chemical and physical parameters of the water samples including pH, EC, TH and TDS were measured using a Hach SensIons system model 156 multiparameter following a standard operating procedure explained by California State Water Resources Control Board (2002). In order to determination of cations and anions amounts in brine, different methods were used, such as flame photometry for sodium and potassium, atomic absorption for calcium and magnesium, silver nitrate for chlor, alkalinity polls for bicarbonate, and measurement turbidity methods for sulfate. The analytical precision for the measured major ions was within plusmn;5%. All of analyses were done in the laboratory of Geological Survey of Iran.Results and DiscussionThe average acidity of brine of the sediment area equals to 8 which indicates alkaline nature of brine. The EC values of the samples vary from 1250 to 14280. Inlet (input) waters of HozeSoltan Lake are poor in bicarbonate ion and its mole ratio is ((HCO3 <3/(Ca + Mg)), so that it has finally created brine type like NaCa(Mg)Cl by making carbonates and gypsum with domination of alkaline earth elements comparing to sulfate. The respective abundance of cations presented in the brine are sodium, magnesium, calcium, potassium and the abundance of anions are chlor, sulfate and bicarbonate. Sodium (average value 75.29 percent) is the dominated cation. Calcium and Magnesium with average values of 18.89 percent and 5.46 percent are the next. Potassium with average value of 0.34 percent is the minimum value. Among the major anions, chlor (47.59 percent) is the dominated anion. Sulfates and bicarbonates (45.34 and 7.05 percent respectively) are the next. Evaporate minerals occurred in sediments are calcite, gypsum, halite, carnallite, hexahydrate, thenardite and basanite.ConclusionHydrochemical studies of inlet waters indicate that mole ratio of ions is HCO3