The Effect of Temporal Changes on the Ecosystem Health of Chehelkhane Sub-Watershed, the Zayandeh Roud Watershed

Extended Abstract Background: According to the opinion of most specialists, the resources and health of the country's ecosystems are being destroyed. In this regard; While preventing destruction and reducing the pressure on ecosystems, it is necessary to be aware of the health of watersheds to plan and manage properly. A healthy watershed is one where natural vegetation has provided the necessary substrate for hydrological and terrestrial processes. In addition, healthy ecosystems are resistant to stress and pressure and provide high quality and quantity of services for the welfare of communities. Thus, assessing the health of ecosystems is important not only in terms of preserving the environment but is also important for the social and economic activities of communities. In this regard, the current research is planned to investigate the temporal changes in ecosystem health indicators using the VOR model in the Chehelkhaneh sub-watershed located in the Zayandeh Roud Watershed. The selection of this watershed for the present study is justified since the Zayandeh Roud Watershed is one of the most sensitive watersheds in Iran and irreparable environmental damage has been caused to this watershed in the last two decades. Methods: To investigate the changes in the health indicators of the Chehelkhaneh sub-watershed, the VOR (power-structure-resilience) model was used during a 10-year statistical period (2011-2021). In this method, V, O, and R represent the production power (function), structure, and resilience of ecosystems, respectively. This model is closely related to the issue of ecosystem stability, which indicates the watershed's ability to maintain its structure and function over time against external factors. To carry out the present study, therefore, land use maps for 2010 and 2010 were first selected from Landsat 5 and 8 satellite images, followed by required pre-processing. Indeed, a false color combination was created using the correlation method between the bands,  and then each of the land use classes was separated from each other in separate stages using the supervised classification method. Next, land cover maps (NDVI) related to the power indicator were estimated after preparing the land use map of the study area. This indicator shows the density of land cover in the region. In the next step, Fragstats software was used to extract structure (SPLIT and PD) and resilience (LPI and AI) indicatorsThe fragmentation (SPLIT), patch density (PD), largest patch (LPI), and aggregation (AI) indices were used for this purpose. It should be noted that the Fragstats software is based on land use. Afterward, standardization was done and the health of the Chehelkhaneh sub-watershed was determined after calculating all the mentioned indicators. Results: Based on the results in 2011, rangeland (42.43%), irrigation and dry farming (30.84%), dry farming (250.30%), irrigation farming (1.14%), and rock (0.30%) had the largest area assigned, respectively. In 2021, irrigation and dry farming (50.95%), rangeland (39.80%), and rocky (9.26%) had the largest area in the region, respectively. In other words, the land use of irrigation and dry farming is dominant in the region, along with the decreased area of natural lands, which indicates the destruction in the study area. In fact, large user units become small units and lead to the disintegration of the region. Moreover, the values of power, structure, and resilience indicators were 0.69, 0.9, and 0.79, respectively, in 2011 and  0.47, 0.71, and 0.64, respectively, in 2021. In this regard, the values of time changes in power indicators in 2011 and 2021 were respectively 0.69 and 0.47, structure values were 0.9 and 0.71, and resilience values were 0.79 and 0.64. It should be mentioned that one of the main reasons for the decrease in the values of health indicators in the Chehelkhaneh sub-watershed is the lack of forest cover and the change in land use to low-yield lands. This important issue has led to a decrease in the quantity and quality of the region's ecosystems. Finally, based on the obtained values of the indicators, the health of the Chehelkhaneh sub-watershed in 2011 and 2021 was 0.49 (Moderate) and 0.21 (partly not healthy), respectively. In this regard, the structure indicator has the most impact on the health of the Chehelkhaneh sub-watershed, and resilience and power indicators have been assigned the next priorities. In other words, the results showed that the effect of the ecosystem’s health indicators was different and the health level of the studied region has decreased over time, which is progressing toward being unhealthy. Conclusion: The present study is new in terms of the comparative investigation of the temporal changes in ecosystem health indicators using the new VOR model and in terms of the attention of managers and experts to the necessity to evaluate the health of ecosystems based on the obtained results. Therefore, the land use change in this region due to the lack of water and the low production potential of the land, which is abandoned after several times of cultivation and is not cost-effective. Hence, it is suggested to carry out protective operations to reduce the destruction of the region with the participation of local communities and hold educational-promotional courses to promote and raise the awareness of the communities. Institutions should be created compatible with the watershed situation while increasing intra- and extra-organizational cooperation in the direction of the policy, laws, and environmental risk management of the projects. In general, it can be acknowledged that conducting the present research contributes significantly to the preparation of the health atlas of the country's ecosystems.