Ecological Assessment of Organic Pollution in the Gorgan Bay, Using Palmer Algal Index

The problem of pollution in the Caspian sea has attracted increasing scientific concerns in recent years, but still, there is limited data relevant to the Gorgan bay. The current study aimed to evaluate the organic pollution of the Gorgan Bay, using Palmer Algal Index. Sampling was conducted seasonally in triplicate from summer 2017 to spring 2018. Phytoplankton samples were collected from surface water (maximum depth of 50cm), using a one-liter sampling bottle and fixed in 2.5% formaldehyde buffer solution. A total of 23 stations were selected including, seven stations in the eastern areas, eight stations in the centre, and eight stations in the western part of the bay. The Palmer Index indicated that all parts of the bay are highly polluted, in the four seasons. Comparison of the index among the three parts of the bay indicated that the central areas are more polluted than other areas in the three seasons, from summer to winter, while only in the spring, the western area of the bay showed the highest value of the index. The predominance of the pollution resistant Phyto-genera such as Oscillatoria, Euglena, Cyclotella, Navicula, Nitzschia, and Synedra supports the classification of the bay as eutrophic. Generally, the results of the algal index revealed that the water quality of the bay has reached a critical level.