عنوان مقاله [English]
Pollution of rivers is one of the important issues related to the environment, which can directly and indirectly affect the health of people, animals and plants that feed on it . Also, rivers are always exposed to various pollutions as one of the fresh water supply sources. The decline in the quality of river water and other surface water sources, due to the entry of industrial and agricultural wastewater, wastewater from treatment plants, the discharge of waste and waste materials in aquifers, has caused an increase in concern about the quality of river water and surface water sources . According to the reasons given, checking the quality of river water is of great importance .
The river studied in this article, the Chalus River, is located in the west of Mazandaran province and originates from the northern slopes of the Kandavan and Taleghan highlands, and flows into the Caspian Sea after traveling about 85 kilometers along the Chalus near Deh Farajabad . This river is called as one of the most important rivers of Iran and it is widely used for agricultural, industrial and urban purposes. This river is also used as a recreational center. For water quality assessment, three stations along this river have been considered for sampling different water quality parameters, the station (ST1) is located upstream of the river due to low human activity. The station (ST2) with more agricultural land and less residential areas is in the middle part of the river and the city of Marzan Abad . Finally, the station (ST3) is located at the end of the river and in the city of Chalus, which has more residential areas than Marzanabad. The investigated parameters include water quality parameters (temperature, PH , electrical conductivity, dissolved solids, suspended solids, turbidity and salinity), oxygen supply (dissolved oxygen, BOD and COD), nutrients (N-NH3, N-NO3 and P -PO4) and faecal coliform. The water quality indicators in this study are the NSFWQI and IRWQIsc water quality indicators, which determine the water quality status by using each of the above parameters and weighting them. By examining the measured qualitative parameters , it is possible to comment on the current state of the river .
According to the results, the optimal range of pH according to Iran's quality standard is 9-5.6, this range in the samples taken from Chalus River was around 7-8 and the pH level does not harm the water quality. The amount of DO varies depending on the concentration of dissolved salts in the water and the biological actions in the water and the temperature of the water. The values of DO varied between 3-11 mg/l , which according to the standard should be more than 5 mg/l . Also, this range of wide changes means that the organic matter in the water in the downstream has increased greatly , which caused a large decrease in dissolved oxygen.The amount of faecal coliform, due to the significant increase of this parameter in the third station, which is located after passing through the city , shows that the urban sewage discharged into the river was not at an acceptable level and caused a significant decrease in water quality . According to the standard regulations, the level of turbidity is equal to 5, and the high level of turbidity in this river can be the result of human activities, such as the extraction of river sand . The obtained results indicate that the quality of river water in ST1 station is suitable and the quality parameters collected in this station are within the range of drinking water standards.But after the first station, when we move to the downstream side of the river, due to the increase in human activities such as road construction on the banks of the river, the entry of agricultural effluents (including dangerous mineral and organic substances, as well as agricultural toxins containing heavy elements dangerous for nature and living beings), Industrial and urban wastewaters greatly reduce the quality of river water.Also, at the time of the study, operations such as sand extraction and removal of the riverbed were carried out, which affected parameters such as turbidity and suspended particles in the water. Finally, by examining the available results, it was concluded that factors such as urban sewage, septic tank, natural and artificial fertilizers in agriculture, soil structure, runoff and stone pebbles in the basin are among the factors of spreading pollution in this river . Also, by examining the quality indicators, the results showed that the NSFWQI index was more strict than the IRWQIsc in checking river water quality . One of the reasons is the difference in the weighting of different parameters in each criterion, for example, in the IRWQIsc index, the highest weighting value was for BOD5, while the weight of this parameter is less in NSFWQI, and in this index, more attention is paid to PH compared to It has become the previous index and has a higher weighting. Among other influencing factors in the difference of this index, we can note that the number of parameters in these two indices are different .
The NSFWQI index recognizes the temperature parameter as an influential factor in determining the quality status of the river , while this parameter is not evaluated in the IRWQISC . But in the IRWQISC index, parameters such as electrical conductivity, concentration of total organic substances soluble in water (COD) and ammonium increased the accuracy of water quality assessment. Among the other points that have been examined is the difference in the quality of the river water in different seasons of the year , which according to the data in tables 5 and 6, we understand that the most polluted time of the river was in spring and summer, where this place is also considered as a recreational center. Also, agriculture is at the peak of activity , so that even in station ST1 there is more pollution than the same station in other seasons.