The fallowing of fish farming cages activity on the loading of nitrogen and phosphorus at water and sediments in the Southern basin of the Caspian Sea: A case study of Nowshahr region

Nitrogen and phosphorus dynamics with fallowing in a fish cage farm were investigated in the Southern of the Caspian Sea-Iranian Coast. Four sampling sites were set: beneath the cages, at the cage sides, ۱۰۰ and ۲۰۰, and ۱۰۰۰ m around the cage farm. The cage culture had a fish yield of a total of ۱۲۳ tons of rainbow trout in the study period. Based on the mass balance equation, ۳۴.۰ kg TN and ۷.۰ kg TP per ton contributed to the cage environment which was probably underestimated. No obvious changes were found at the sampling sites ۲۰۰ and ۱۰۰۰ m around the cages during the study periods. The mean TPw and TPs compared to most of many years were not increased but the concentration of TNw and TNs, in the present study, was more than in previous studies but which indicates the impact of aquaculture activities on the region, but as noted above, most of these variables have not exceeded the standard of aquaculture threshold. These results indicated that at its present production level, the farm had short-term, localized impacts on the Caspian Sea environment. Also, the main impacts were found close to the cages (beneath the cages and at the cage side); the sampling points at the cage side showed relatively high TN and TP sedimentation. After breeding, water TN and TP decreased significantly but the sediment TN and TP contents remained high. Therefore, recovery seems to happen during the fallowing period but attention should be paid to whether the culture continues to operate in the future.

کلیدواژه ها:

Cage fish farm ، Nitrogen and phosphorous loading ، Fallowing ، Caspian Sea