Eutrophication Trend of Anzali Wetland Based on 1992-2002 Data



Anzali wetland on the south west of Caspian Sea is a unique ecosystem was registered as Ramsar site at 1975. Anzali wetland was deteriorated due to numerous disorder and poor water quality. The riverin input were strongly affective in the process of eutrophication where the eastern and central region was more degraded. The first survey on the eutrophication process was conducted at 1969, since then several other investigations reported too. This survey was conducted on several study sites at period from 1991 to 2000. For evaluating eutrophication degree the trophic model of chlorophyll-a, total phosphorous and nitrogen also total phosphate to total nitrogen index were used. The result showed that the mean Chlorophyll-a concentration is above of 25 µg/l. and the nitrogen and phosphorous concentration were between 0.15-1.5 mg/l and 0.17-0.05 mg/l. respectively. On the based of trophic level of chlorophyll-a, total phosphorous and total nitrogen 87-100 % of wetland is eutroph however at early years about 46-90 % of the surface area were eutroph indicating that the trend of eutrophication increasing. Trophic models of phosphate to nitrogen shows the most part of Anzali wetland is in the extreme mesotrophic level close to entropic zone. The average entropic index value was 46 with respect to other characteristic of wetland appear to be low. According to TSI (PN) less than 5.2% surface area of Anzali wetland is entropic state status. Anzali wetland does not have enough capacity to reduce all anthropogenic loads from its watershed area therefore the first effective activity is to prevent nutrient load input of wetland. The restoration of Anzali wetland is suggested base on previous investigation recommendations and with revising some of them.