Document Type : Research Paper
Authors
Caspian Sea Ecology Research Center (Sari, P.O. Box 961, Iran),
Abstract
The Khersan River, the largest tributary of the Karun River, is regulated by the Khersan-3 Dam, constructed for flood control, irrigation management, and hydropower generation. Despite its strategic importance, no comprehensive study has previously assessed microbial water quality in this reservoir, particularly under the pressure of intensive agricultural activities in the watershed. This study investigated heterotrophic bacteria, total and fecal coliforms, and protozoan (Giardia and Cryptosporidium) contamination in the Khersan-3 sub-basin. Monthly sampling was carried out from November 2023 to October 2024 at five stations using sterile glass bottles (100 ml) from the surface layer (20 cm depth). For protozoan detection, 10 liter samples were collected at Station 5.
Results showed seasonal and spatial variations in microbial indicators. The highest mean concentration of heterotrophic bacteria was observed in autumn 2023 (6.237 Log CFU/100 ml), while the lowest occurred in summer 2024 (4.507 Log CFU/100 ml) (p< 0.05). Total coliforms reached their maximum in winter 2023 (3.822 Log CFU/100 ml) and decreased to a minimum of 2.509 Log CFU/100 ml in summer 2024 (p< 0.05). Seasonally, significant differences were observed, with higher bacterial loads in autumn compared to summer (p<0.05). Across sampling sites, Station 5 showed significantly greater bacterial densities than other stations (p<0.05). Cryptosporidium was undetected in all samples, whereas no significant difference was found in Giardia occurrence among seasons, despite detection in approximately 40% of spring samples (p>0.05).
This study provides the first evidence of substantial temporal and spatial fluctuations in indicator bacteria across the Khersan-3 Dam watershed, highlighting the influence of hydrological and anthropogenic drivers. The findings emphasize the need for targeted management actions, including continuous microbial surveillance, stricter control of agricultural runoff, and improved water treatment practices to safeguard public health and aquaculture sustainability.
Keywords
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