Investigation of Valasht Lake Trophic State Based on TSI Index

Background and Objective: In the present study, trophic state of Valasht Lake was investigated monthly at 3 stations, from December 2008 to December 2009. The purpose of this study is investigating the trophic state of the lake and introducing the basic solutions to maintain this valuable ecological resource.  Method: Trophic state index (TSI) was used in this study. Also, the effective parameters on primary production and trophic state determined in this study include: total phosphorus (TP), total nitrogen (TN), a-chlorophyll, Secchi depth (SD), and TN/TP ratio.The results from all mentioned parameters were compared with different trophic levels of fresh water lakes published by U.S Environmental Protection Agency and Organization for Economic Cooperation and Development. According to trophic state index and based on nutrient levels (phosphor and nitrogen), Valasht lake is classified in Mesotrophic to Eutrophic state and based on the other mentioned parameters, it is classified in mesotrophic state. Results: Mean rate of trophic state index reveals the mesotrophic state in this lake. According to the results of Red Field ratio and TSI, nitrogen and turbidity, especially in wet (rainy) seasons, are the main determinative parameters in primary production in Valasht Lake.