Determining the Origin of Chemical and Biological Pollutants in the Water of Mighan Wetland in Arak

Pollution of wetlands is important because, in addition to damaging the ecosystem of a wetland and destroying living organisms, it can also be dangerous to the health of people living nearby. The entry of chemical fertilizers, municipal sewage, hazardous hospital and industrial wastewater into the wetlands, as well as the disposal of waste in their vicinity, can contaminate the wetland. One of the most important factors that put wetlands in a serious danger and has a very destructive effect on their fauna and flora is biological pollution caused by human activities and land use. Wetlands’ water resources often contain chemical impurities. These impurities are caused by air pollution, soil pollution, or pollutants caused by human activities that are discharged into the environment in the form of solid and liquid waste. In addition to human activities affecting wetland pollution, the natural conditions prevailing in the wetland area are also effective in the chemical composition of wetlands. The rocks above each wetland determine the chemical composition of its water and soil resources.The central wetlands of Iran, including the Mighan Arak wetland, are mostly saline and their salinity has reached the groundwater aquifers of the adjacent plains due to human interference. This phenomenon, which has been a kind of human pollution under the advancing salinity front in aquifers, is seen in most coastal aquifers and central aquifers in Iran. Arak Mighan wetland is one of the wetlands of central Iran that is salty. Local and migratory birds, local animals, and aquatic animals benefit from the Mighan wetland. The most important water sources that feed the wetland are groundwater, treated wastewater from the city of Arak, and surface runoff in the wet months. The purpose of this study is to identify the chemical and biological pollutant variables of wetland water in comparison with drinking standard water to identify chemical and biological pollutant variables and to determine the most important natural and human sources of pollution in wetland water pollution using multivariate statistical analysis.

Arak watershed with an area of ​​5500 Km2 is a closed area. About 62% of the area is covered by highlands, 36% by plains, and 2% by the Mighan wetland. The average annual temperature and rainfall in Arak are 14º and 350 mm, respectively. The wetland consists of two parts: the island in the center, and the lake around the island which has an average water depth of half a meter. The Mighan wetland alluvium with a thickness of 300 meters is located on the limestone rocks of Cretaceous formation. Thirty-two water samples in the fall of 1397 (2018) from different uses (6 island samples, 6 lake samples, 10 agricultural well samples, 1 sample of Amlah company, 2 industrial effluent samples, 4 Arak urban sewage samples, and 3 repeated samples to determine the results tests) were taken from the lagoon and surrounding water resources. The measured variables included: electrical conductivity, calcium, magnesium, potassium, sodium, chlorine, sulfate, fluorine, nitrate and phosphate, bicarbonate, BOD, and COD. The accuracy of the data was about one milligram per liter.The data were analyzed using Excel, Statistica, RockWare, and ArcGIS software. Among the various variables, 11 of the chemical and biological variables were selected and their concentrations in saline and freshwater were compared with the international drinking standards.

The water is concentrated in the Mighan wetland of Arak in the two uses of the ponds (ponds resulting from the extraction of sodium sulfate in the central island) and the lake (around the central island). Uses such as mineral water wastewater, Arak municipal treated wastewater, industrial effluent, and agricultural wells are considered as potential sources of pollution for the water of the Mighan wetland. The high concentration of chemical compounds such as EC, TDS, SO4, and Cl above the drinking standard showed the nature of the salinity of the water in the Mighan wetland. A study of the salinity origin of Mighan water showed that salinizing variables such as SO4 and Cl anions, as well as cations such as Na and K, were related to gypsum and salt rocks in the northern highlands (Ashtian region) of the Mighan area. A similar trend has shown that the dissolution of evaporative minerals from the heights of the Torbat-e Heydariyeh plain and transfer to groundwater has caused all of the plain's waters to be of the sodium chloride and sodium sulfate types. An examination of the inflows of surface water and groundwater to the Mighan wetland showed that the northern waters of the wetland had the SO4-Cl-Na type and the southern waters had HCO3-Ca type. Mixing of surface water and groundwater with the Mighan wetland water has caused the SO4-HCO3-Na-Ca type. The effluent of the Iranian Salt Company (extracting sodium sulfate from the basins of the central island) had high EC, TDS, SO4, and Cl. About 60 percent of the water in the wells around the wetland, which was used for agriculture, was almost salty due to the high EC, TDS, SO4, and Cl. The compatibility of SO4 and Cl agricultural waters was almost salty with SO4 and Cl. The Mighan wetland water indicated the salinity of the region’s wells from the wetland water. A similar trend of groundwater salinization in the Shabestar plain indicated the infiltration of saline water from Lake Urmia into the groundwater aquifer of the adjacent plain.Factor analysis was used to determine the relationship between chemical compounds and to investigate the origin of compounds. In factor analysis, three factors explained 88.9% of the variance. The first factor ( 56.96%) included EC, TDS, SO4, and Cl. Thsecond factor included F, NH3. The third factor included PO4, HCO3. Given the first factor of factor analysis and the effectiveness of variables such as EC, TDS, SO4, and Cl, as well as the increase in this factor in the zoning map to Mighan wetland, it is obvious that the salinity of the wetland and effluent of the company is natural salts, while the salinity of the wells around the Mighan lagoon is the result of  human activity. In the zoning map, the second factor with variables F, NH3 had a focus on the water area of ​​the wetland (island and lake) of Mighan. Also, due to the high share of NH3 (0.91) compared to F (0.84) in factor analysis, the increase in NH3 was the human factor while F was the natural factor. On the other hand, F, SO4, and Na have are found in waters that have been under the influx of brackish water from the Mighan wetland; therefore, F in the water of the wetland has a natural origin. The presence of F in some water of agricultural wells indicated the infiltration of saltwater in the Mighan wetland. On the other hand, NH3 is found in only a small number of water samples in the Mighan wetland (ponds and lakes), which is higher than the standard drinking level. NH3 is a source of organic nitrogen compounds and bacteria. The third factor involved factor analysis of PO4 and HCO3, in which the role of PO4 was more pronounced. The PO4 of Mighan Lake, urban sewage, and industrial wastewater were far higher than the standard. Phosphate was introduced into surface, groundwater, and wetlands through domestic wastewater (containing synthetic cleaners) or agricultural effluents, or industrial wastewater. Phosphorus is one of the essential elements for the growth of algae. More than 70% of the phosphorus compounds in wastewater are due to the use of detergents. Since the concentration of PO4 in treated wastewater is very high, sewage is the source of human pollution in the wetland. On the other hand, the high concentration of PO4 in the water entering the wetland has caused a large growth of plants in the area.The concentration of bicarbonate ions (HCO3) in the water composition of Mighan Wetland Lake and some wells in the southern part of the Mighan wetland was high while its concentration in other waters was lower than the standard. Bicarbonate indicates thepresence of limestone. Due to the dissolution of calcareous and dolomite rocks, bicarbonate compounds have been obtained that have been directed to surface and groundwater. The southern part of the Mighan wetland is composed of Cretaceous limestone and dolomite rocks, which have been the most important source of bicarbonate of water in the Mighan wetland and wells in the region. High levels of bicarbonate ions are natural contaminations that are not controlled by humans.Studies have shown that in saline waters with a chlorine concentration of more than 35,000 mg per liter, even if there are small amounts of organic matter, the amount of BOD and COD is exaggerated. Since the water of the Mighan wetland has a Cl of more than 35000 mg per liter, so BOD and COD in the water of the wetland have not been suitable criteria for biological pollution.

Arak’s treated municipal wastewater, the effluent of the Minerals and Industries Solutions Company, as well as the surrounding groundwater have been the most important sources of human pollution that have the potential to pollute the wetland’s water. Due to the fact that groundwater is located downstream of agricultural lands and large industries, no chemical and biological pollutants from agricultural and industrial effluents have been seen in the water of the Mighan wetland. Arak treated wastewater is the most important source of water entering the wetland, which has introduced phosphate and ammonia into the water of the wetland. Therefore, the water of the Mighan wetland is without chemical and biological pollution and the only effect of the wetland can be the salt forward. This phenomenon is due to the drop in the groundwater level in the region with human intervention. Therefore, basic measures must be taken to raise the groundwater level during the aquifer management operations in the plains around the wetland and to control the drainage of wells and the removal of unauthorized wells.