Investigation of sediment chemistry parameters around the fish cage culture sites in the southern part of the Caspian Sea (Nowshahr region)

The establishment of aquaculture cages in the right place will be associated with the least adverse effects on the ecosystem, so the quality of sediment is very important in monitoring fish cages farming. The aim of this study was to investigate the sediments chemistry parameters around fish cage culture in the southern of Caspian Sea (Nowshahr region). Sampling was conducted in four stages of the breeding period during 2017 and 2018, underneath the cages and at 200m and 1000 m longitudinal distance in four geographical directions from the cages. Based on the results the variations in different forms of phosphorus such as Loosely-P, Fe-P, Al-P, Bioava.-P, Ca-P, TIP, Res.-P and TP were 1.2-13.8, 22-114, 12-121, 37-211, 61-2170, 150-2223, 0-937 and 203-2283 µg/g. dw, respectively. The order of different forms of phosphorous were registered as Ca-P>Res.-P >Fe-P>Al-P>Loosely-P. The variation range of pH, Eh and TOC% were 8.05-8.60, (-63)-(-83) and 1.36-7.87, respectively. The results revealed that temperature, Eh and pH had the main role in the adsorption and release of loosely-P, Fe-P and Al-P. Comparison of 25-75th percentiles of total organic carbon (1.97-2.60%) with permissible threshold showed that the sediments of Nowshahr region can be classified as moderately polluted.