Spatio-temporal dynamics of eutrophication in Anzali international wetland system using a trophic state index

Authors

1 Department of Environmental Science, Faculty of Natural Resources, University of Guilan, P.O. Box 1144, Sowmeh Sara, Guilan, Iran

2 Inland Waters Aquaculture Research Center, Iranian Fisheries Sciences Research Institute (IFSRI), Agricultural Research, Education and Extension Organization (AREEO), Bandar Anzali, Iran

3 Department of Animal Sciences and Aquatic Ecology, Ghent University, 9000 Ghent, Belgium

Abstract

Eutrophication phenomenon is a global concern in wetland ecosystems. In the present research, the trophic state index (TSI) was initially determined in four main parts of the Anzali wetland using Carlson's TSI. Then, the key variables driving the eutrophication phenomenon were identified in the wetland using principal component analysis (PCA) and classification tree model (CT). Sampling was conducted monthly at 4 different and main parts of the wetland for one year (April 2019-March 2020). Based on the TSI results, all sampling sites are categorized as a hypertrophic state. However, among the sites, the Pirbazar and Sorkhankol had the highest (88.44) and the lowest TSI (76.86), respectively. The decrease in the ratio of total nitrogen (TN) to total phosphorus (TP) in the Pirbazar (5.54), shipping channel (6.58), and Sorkhankol (9.27) indicated the limitation of TN in these sites. On the contrary, the high ratio of TN/TP in the Abkanar (14.85) indicated the limitation of TP in this section. The low average ratio of the TN to TP in the four different parts of the wetland (9.06) revealed the limitation of TN in the entire wetland. Considering the TSI average in the whole wetland (22.83), it can be concluded that all parts of the wetland are classified as a hypertrophic condition. Based on the PCA biplot (the first component), the most influential factors driving the eutrophication in the wetland were TP, water transparency and chlorophyll-a (chl-a), respectively. According to the CT model’s prediction, water temperature, TP, and water transparency contributed more than other factors to the wetland eutrophication process.

Keywords

Iranian Journal of Fisheries Sciences
Volume 24, Issue 2
March 2025
Pages 177-191

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