Biogeochemistry of the Mahaweli River, Sri Lanka

The Mahaweli is a major river located through the center of Sri Lanka; the river and its reservoirs serve as a source of water for many communities as well as the primary source of water to the Eastern Sri Lankan coastal ocean. At 335 km in length, the Mahaweli is the longest river in Sri Lanka, with a drainage basin consisting of approximately 1/7^th of the total runoff in Sri Lanka. Covering nearly 17% of the total landmass of the island, the drainage basin encompasses 10,448 km² and the river totals an average mean annual flow of near 6.5 x 10¹² kg/yr. The river’s drainage basin is also within both high and low-lands and dry and wet zones, flowing through a variety of climatic biomes present in Sri Lanka, including much agricultural land. Given the size and volume of the river and its drainage basin and the prevalence of farming practices throughout much of this area, characterization of the biogeochemistry of the river and its inputs to the coastal ocean is important to the understanding of the coastal system. The biogeochemical gradients along this river have not been previously quantified, nor have the loadings to the adjacent coastal waters. Thus, in this study we present a gradient of 30 sampling stations across the Mahaweli River catchment to evaluate trends in nutrients, organic carbon, trace metals and target agrochemicals. This work serves as a baseline study in understanding both the along river and coastal biogeochemical concentrations, transitions, and coastal export of carbon and other key species in this tropical region and can inform future efforts to track and understand the impacts of central Sri Lanka’s water resources on the coastal ocean.