ارزیابی مکانی – زمانیﻛﻴﻔﻴﺖ آب رودﺧﺎﻧﻪ ﻗﺮه ﺳﻮ اﺳﺘﺎن ﮔﻠﺴﺘﺎن ﺑﺎ اﺳﺘﻔﺎده از ﺷﺎﺧﺺ IRWQI

Spatial-temporal assessment of water quality in the Qarh Soo River Basin, Golestan Province using the IRWQI index
Moslem Mohamadi BaghGolbon1 , Ali NajafiNejad*2 , Khalil Ghorbani3 , Arash Zare Garizi4
1-Moslem mohamadi Baghgolbon, Ph.D. Student, Dept. of Watershed Management, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, E-mail: moslemmohamadi721@gmail.com.
2-Ali nahjafinejad, Professor, Dept. of Watershed Management, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, E-mail: najafinejad@gau.ac.ir.
3-Khalil Ghorbani, Professor., Dept. of Water Engineering, University of Agricultural Scinces and Natural Resurces, Gorgan, Iran, E-mail: ghorbani.khalil@gau.ac.ir.
4-Arash Zare Garizi, Assistant Prof, Dept. of Watershed Management, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, E-mail: arash.zare@gau.ac.ir
Abstract
Population growth, urbanization, industrialization, and expansion of agricultural activities have placed severe pressures on water resources, especially surface waters. As one of the most important sources of freshwater supply, rivers play a vital role in meeting the needs of drinking water, agriculture, industry, and electricity generation. However, due to the discharge of domestic and industrial wastewater, agricultural runoff containing fertilizers and pesticides, unprincipled disposal of waste, and extensive human activities, the quality of these resources is being significantly degraded. This has made sustainable management of water resources one of the major challenges at the national and international levels. Therefore, regular monitoring and assessment of river water quality through scientific and reliable tools is an inevitable necessity. One of these efficient tools is the use of the Water Quality Index, which combines physical, chemical, and microbial parameters to provide a comprehensive and understandable picture of the overall water quality status.
Background and Objectives: In this regard, the present study aimed to evaluate the spatial and temporal water quality of the Gharesu River in Golestan Province using the IRWQI (Iranian Water Quality Index for Surface Waters). Gharesu River, with a basin area of 1782 square kilometers, is one of the important watersheds of Golestan Province, originating from the heights of the Northern Alborz Mountains and flowing into Gorgan Bay after passing through agricultural and urban areas. This river constitutes about 8 percent (nearly 100 million cubic meters) of the surface water resources of the province and is affected by numerous human activities, including agriculture, animal husbandry, industry, and urbanization. The highest precipitation is 876 mm at the Alangdareh station and the lowest is 260.34 mm at the Haji Abad station. The climatic characteristics of the region are Mediterranean, semi-arid and semi-humid according to the Demarton classification system. The land use of the basin is characterized by forest lands (including dense canopy forests, medium canopy forests, low canopy forests and very low canopy forests.In this study, sampling was carried out seasonally (once per season) over four years (2010 to 2013) from 7 sampling stations along the river. The stations included: Tuskistan, Seyyed Masoud, Ghorbanabad, Qara-Tapeh, Niazabad, Qara-Su and Masab, which are located from upstream to downstream. At each sampling time, 11 water quality parameters including pH, temperature, turbidity, dissolved oxygen (DO), electrical conductivity (EC), BOD, COD, ammonium (NH₄), nitrate (NO₃), phosphate (PO₄), total hardness and fecal coliform were measured. Physical parameters were measured on site and with calibrated portable devices, and other parameters were analyzed after the samples were transported to the laboratory and under standard conditions (storage on ice), using standard laboratory methods.To assess water quality, the IRWQI index software was used, which was developed in collaboration with Shahid Beheshti University and the Environmental Protection Organization. This index is calculated according to the weighting of the effective parameters and classifies water quality into five categories: relatively good, average, relatively bad, bad and very bad.
Findings: The results showed that the water quality of the Qarasu River decreases significantly from upstream to downstream. The best water quality was recorded at the Tuskistan station (upstream) in the winter with an index value of 59.7 and a "relatively good" category. This improvement in quality is due to the lack of direct impact of agricultural and industrial activities and access to fresh water from natural sources. In contrast, the lowest water quality was observed at the Qara-Tepe station in the summer with an index value of 10.4 and a "very bad" category. This indicates severe pollution of this part of the river, mainly due to the discharge of urban and industrial wastewater, agricultural runoff containing fertilizers and pesticides, and a decrease in the river flow rate in the warm seasons of the year.Seasonal analysis showed that water quality in the summer is generally lower than in the winter. This decrease in quality is due to a decrease in the river flow rate, a decrease in the dispersion and decomposition of pollutants, an increase in water temperature, and an increase in microbial activity, which leads to a decrease in dissolved oxygen and an increase in BOD and fecal coliforms. In winter, with increased rainfall and river flow, the dispersion of pollutants is better and water quality improves.The parameters BOD, phosphate, nitrate, fecal coliform and turbidity were identified as the most important factors affecting the decline in water quality. High values of these parameters indicate organic and nutrient pollution resulting from agricultural activities (use of chemical fertilizers), animal husbandry and sewage discharge. Also, the stations of Qurbanabad, Niazabad and Masab were in the "bad" or "relatively bad" category in all seasons, indicating the persistent impact of pollutant sources in these locations.
Conclusion: Finally, the findings of this study emphasize the need for comprehensive management plans to control pollution in the Qarasu River. Key recommendations include: thorough treatment of industrial and municipal wastewater before discharge, control of fertilizer and pesticide use in agriculture, implementation of biological pest control methods, and continuous monitoring of water quality at sensitive stations. Also, the IRWQI index is recommended as a simple, reliable, and efficient tool for rapid water quality assessment and management decision-making.This research is an important step towards identifying critical pollution points, understanding the spatial-temporal patterns of water quality changes, and providing practical solutions for protecting this vital resource. Also, its results can be used as a basis for future planning in the field of water resources management, developing environmental policies, and increasing public awareness about the importance of river protection.

Keywords: Qara Su River, water quality, IRWQI index, physicochemical and microbial quality.