Channel mobility-driven hydrological connectivity controls water surface area variations in oxbow lakes

Oxbow lakes serve as rich habitats for wildlife, natural contaminant filters, and an essential source of sustenance and prosperity for riverine communities around the world. Despite their significance, little is known about their interannual hydrological variations, how these are controlled, and the impact they have on lake physiochemistry. Without an understanding of how these environments currently function, it will be challenging to protect them from the pressures of climate change and land use conversion, thus threatening their ability to deliver a range of ecosystem services in the future. Data from 76 recently formed (1984-2022) oxbow lakes along two near-pristine Amazonian tributaries in Bolivia are presented to evaluate the role of rainfall and channel connectivity in driving variations in water surface area (WSA) over interannual timescales. These results were extracted from multispectral satellite imagery using a range of semi-automated workflows leveraging a range of band rationing techniques. Over interannual timescales, lakes were observed to diminish by up to 97% and increase by over 200% relative to the WSA in the previous year. Seasonal rainfall and the proximity of the active channel were used to discern predominant controls on WSA variations and demonstrated that active channel proximity was important, particularly where established flow pathways were present. Rainfall was more important for lakes in the distal floodplain. Changes in hydro-climate, flow regulation, and land use will alter these key hydrological controls in fluvial systems, thus potentially altering the functioning of lakes in the future and threatening those communities who rely on the lakes for survival.