Investigation of Rainbow Trout Farm Effluents on Water Quality of Humestan River (Isfahan, Iran)

In the present study, the impact of effluents exiting from four rainbow trout farms on the water quality of Humestan River (Isfahan, Iran) across 11 stations was investigated. Water samples were collected in the spring, summer, fall and winter and such factors as dissolved oxygen, pH, BOD5, COD, ammonia, nitrite, nitrate and phosphorus were measured. The results showed that the amounts of phosphorus entering the River during spring, summer, fall and winter were 311.8 kg, 408.1 kg, 408 kg and 683.1 kg, respectively. Furthermore, the amounts of nitrogen entering the River during spring, summer, fall and winter were 1653.75 kg, 2164.05 kg, 2164 kg and 3622.5 kg, respectively. The amount of BOD and COD in all sampling stations and in all four seasons was less than 5 and 10 mg/lit, respectively. Due to the very low concentration of ammonia in water samples, no number was reported on the part of laboratories in this case. The amount of nitrite in all four seasons significantly exceeded the recommended level (0.02 mg/lit) (P <0.05). Given the whole year, it was indicated that the amounts of nitrate and total nitrogen were significantly less than the conventional level (2 mg/lit) (P <0.05). Moreover, the minimum and maximum amounts of phosphate were reported in the spring and winter, respectively, and this amount did not significantly exceed the critical level in any of the seasons (0.5 mg/lit) (P >0.05). In general, fish farming and effluents imported into Humestan River affected the water quality thereof.