Survey of Temporal and Spatial Changes of Vegetation and Water Body of Anzali Wetland Using Remote Sensing Indices and Google Earth Engine

Wetlands play an important ecological role in the balance of ecosystems. The excessive increase of aquatic plants causes important changes such as eutrophication, increase of water turbidity, swamping and finally drying of the wetland. Using the time series of satellite data in the Google Earth Engine is an efficient and useful way to investigate the ecological conditions of wetlands. Due to the importance of Anzali Wetland and its complex and strategic conditions, temporal and spatial changes of the vegetation and water body of the wetland were studied using Landsat satellite (TM), (ETM+) and (OLI) sensor data from 1990 to 2020 in Google Earth Engine. Vegetation changes were evaluated using the (NDVI) index and (mNDWI) index was used to study water body changes. The results show the surface of the wetland water body has decreased by 5520 hectares (20%) during the three decades of study, dense vegetation covers have decreased from 7756 to 5350 hectares and semi-dense vegetation has increased from 6967 to 14100 hectares, according to the sampling, these changes were confirmed. By examining the annual precipitation in Guilan province, based on TRMM satellite rain data, it was found that the precipitation factor has a nonsignificant role in reducing the water body of the wetland. And due to human interventions through the introduction of river sediments and the pollution load resulting from the entry of agricultural, urban and industrial effluents into Anzali Wetland, as well as the reduction of the amount of water in the rivers leading to the Wetland due to their excessive use in the upstream of the basin, the water body of the Wetland has decreased and semi-dense vegetation has increased.