Integrated River-Estuary Modeling to Assess Spawning and Habitation Area for Caspian WhiteFish in Response to Upstream Pollution Sources (Case Study: Tajan River Estuary)

Despite the ecological importance of the estuaries draining into the Caspian Sea, there is insufficient information about their fish habitats. The Tajan River is an excellent habitat for native and migratory fish species, including Caspian whitefish. Even with the environmental and economic value of Caspian whitefish, the vital parameters of this species have not been quantified and modeled, primarily since the effect of upstream pollution load on their livable volume has not been investigated. In this study, we investigate the suitability of the estuary for spawning and the habitat of Caspian whitefish based on their vital need for dissolved oxygen and temperature. We determined the share of each pollution source around the Tajan River. Then using these data, we calculate the receiving pollution load into the estuary using the QUAL2K model. In the next step, we developed the CE-QUAL-W2 model and added the critical spawning and habitat parameters of Caspian whitefish to the model equations. Finally, the habitable volume for Caspian whitefish is identified, and we examined the conditions of the Tajan estuary under three different scenarios. The results showed that in the period from March 10 to April 10, a suitable volume of the estuary has the conditions for the migration of Caspian white fish. However, the bed layer has suitable conditions for the growth of white fish eggs from March 22, so the eggs released before this date are destroyed. In addition, reducing the BOD load of urban and rural sources has the highest impact on the water quality in the estuary. It can significantly improve the living and spawning conditions of Caspian whitefish.