Discerning hydrological controls on the behaviour of water surface area changes 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 the controls on oxbow lake hydrology and the timescales over which they operate. 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 the wealth of ecosystem services they currently provide, in the future. Here we present an analysis of the temporal behaviour of 110 recently formed (1984-2022) oxbow lakes in the near-pristine catchments of three Amazonian tributaries and elucidate the hydrological controls on this behaviour using a combination of band-rationing procedures and tropical rainfall data. We demonstrate that water surface areas (WSA) fluctuate annually, with some increasing in size by >60% compared to the year immediately following formation. We found that seasonal and annual rainfall exerted a strong control on annual variations in WSA, while proximity of the lakes to the mainstem was less important. Proximity of the lake to the mainstem became more important where flow could be directly conveyed through tie channels or breaches in the lake plug. Changes in hydro-climate, flow regulation, and land use will alter the dynamism of lake hydrology, thus potentially altering the functioning of lakes in the future.