چكيده به لاتين
One of the most important threats to lakes is the phenomenon of eutrophication, which means the enrichment of the water body with nutrients, which causes excessive growth of algae and plants in the lake. Human activities have increased the rate and extent of eutrophication due to the ever-increasing depletion of point and non-point sources of nitrogen and phosphorus nutrients in aquatic ecosystems, which has had significant consequences on lake biodiversity, water quality, the fishing industry, and recreational and tourism opportunities. Increasing urbanization and agricultural and industrial activities lead to the release of phosphorus and nitrogen into water bodies, and are the main activities that affect the nutrient status of lakes. In general, the aggravation of man-made factors along with changes in natural factors (mostly climatic) have accelerated the growing process of lake nutrition during the past decades. In this research, due to the high economic-social-political-social importance of the Caspian Sea as a water area enclosed between 5 countries, the temporal and spatial investigation of the eutrophication status in this water body was investigated in the time frame of 2002 to 2021. In this research, monthly satellite data of chlorophyll-a and climate parameters including precipitation, wind speed, cloudy, sea surface temperature, photosynthetic radiation and air temperature were extracted for the Caspian Sea region. In situ measurements of chlorophyll-a were also used to evaluate the accuracy of the data obtained from MODIS-Aqua and obtain the values of deep chlorophyll-a maximum (DCM) in the southern Caspian Sea. To investigate the effect of climatic drivers on the eutrophication of the Caspian Sea, this sea was divided into 14 regions and the median and 95th percentile values of each of the mentioned parameters were calculated in each region. Then, using the Mann-Kendall test and the Sen's estimator of slope, the trend of monthly, seasonal and annual changes in the concentration of chlorophyll-a in each part of the Caspian Sea was calculated. The findings of this research showed an acceptable correlation between the satellite data of chlorophyll-a and the data measured in site (R2 = 0.74). The results of the changes in chlorophyll-a showed an increasing trend in the North Caspian, while the Kara-Bogaz-Gol Bay and the South Caspian (coasts of Iran and Azerbaijan) showed a decreasing trend. Also, no significant trend for chlorophyll-a changes was observed in the Middle Caspian. The main climatic factors affecting the concentration of chlorophyll-a on a monthly scale in the entire Caspian Sea were sea surface temperature, photosynthetic radiation and air temperature, respectively. The results of this research, in addition to depicting the spatial and temporal trend of eutrophication in the Caspian Sea, can be used in the foundation of a transnational and regional program for the sustainable environmental use of this lake.
