Physicochemical conditions and trophic levels of the Anzali Wetland

Anzali wetland is one of the most important wetlands in the southern coast of the Caspian Sea which is under the influence of the brackish water of the Caspian Sea and the freshwater rivers entering it. Therefore, it plays important role as an exclusive ecotone. Physicochemical conditions and trophic levels of the Anzali Wetland were evaluated monthly from May 2014 to May 2015. Trophic State Index (TSI) was calculated based on the evaluation of chlorophyll a, total phosphorus (TP), total nitrogen (TN) and water transparency. The results showed that the average annual amounts of total nitrogen, total phosphorus and dissolved oxygen were 1.023±0.523, 0.113±0.105 and 8.71±2.63 mgL^-1, respectively. The amounts of total nitrogen were not significantly different among various research locations (P>0.05), whereas the amounts of total phosphorus were significantly different among various research locations (P<0.05). The amounts of chlorophyll a ranged from 0.6 to 329.1 µgL^-1 (with the average amount of 47.4±65.0 µgL^-1). The amounts of EC ranged from 254 to 14250 µm/cm which were significantly different among various research locations (P<0.05).The TN/TP ratio was lower than 10 in all research locations except in the western part of the Anzali Wetland which indicated that phosphorus was the limiting factor for eutrophication. According to the results, the western part of the Anzali Wetland and Siah-Keshim area were eutrophic and super-eutrophic, whereas the other regions of the Anzali Wetland were classified as hypereutrophic. Controlling and decreasing the amounts of nutrients from inlet waters and controlling the growth of aquatic plants in the Anzali Wetland can be used to improve the quality of water and to control eutrophication.