Examining the Effects of Land Use, Salinity Gradient, and Water Pollution on Greenhouse Gas Emissions in Urbanized Estuaries.

ABSTRACT

Estuaries are significant contributors to greenhouse gases (GHGs) in waterways. However, the effects of human activities and ecological variables on GHG emissions in estuaries remain poorly understood. This study examines the patterns and causes of GHG emissions in the Scheldt Estuary, focusing on the roles of salinity, water contamination, and land use. The findings indicate that salinity negatively impacts the release of carbon dioxide (CO2) and nitrous oxide (N2O), likely due to reduced salt levels and cleaner water upstream. Water contamination's influence on GHG emissions was more pronounced in cleaner, upriver sites compared to saltier downstream locations. Specifically, CO2 emissions quadrupled, and N2O emissions tripled as water conditions worsened from healthy (near the mouth, bordered by agricultural land) to polluted (farther downstream, bordered by urban areas). Methane (CH4) emissions were significantly higher in aquatic locations than in salty sites. The reduced impact of contamination from downstream to the river mouth may be due to increasing population density. Urban sites emitted about twice as much CO2 and N2O as those in natural and industrial areas. Machine learning analysis also showed that fertilizers and organic enrichment, along with salinity, significantly increased GHG emissions. These results highlight the importance of understanding the interplay of salinity, water contamination, and land use in influencing GHG emissions in coastal ecosystems.