Improvement of Bio-Optical Characteristics of Seawater in the Southern Caspian Sea Basin Triggered by COVID-19 Lockdowns: Insights from Remote Sensing Data

Multiple studies have demonstrated that human activities have significant impacts on aquatic ecosystems, particularly in coastal areas. The COVID-19 pandemic, along with the sharp decline in industrial, transportation, and tourism activities, provided an opportunity to examine the impact of these changes on seawater quality in this study, using MODIS-Aqua satellite data, changes in key seawater quality indicators, including chlorophyll-a, dissolved organic matter, and suspended particles, were evaluated in the coastal and offshore areas of the Southern Caspian Sea basin during pre-lockdown and lockdown periods. The data analysis results showed a significant reduction in chlorophyll-a concentration in coastal areas and in dissolved organic matter in both coastal and offshore areas during the lockdown period. More specifically, this reduction was 24.9% and 40.7% for chlorophyll-a, and 22.1% and 19.5% for dissolved organic matter in coastal and offshore areas, respectively. The decline in these indicators reflects an improvement in seawater quality and a reduction in organic pollutant loads in these areas. The findings of this study highlight that reduced human activities have visibly positive effects on marine aquatic ecosystems. Therefore, continuous monitoring of bio-optical parameters changes and improving wastewater treatment processes before discharge into aquatic environments are of particular importance. This study also demonstrates that global pandemics can provide experimental opportunities to study the effects of human activities on the environment.