Twenty-three-year timeline of ecological stable states and regime shifts in upper Amazon oxbow lakes

Abstract

Regime shifts in shallow lakes are often associated with anthropogenic impacts, such as land-use change, non-point source nutrient loading, and overfishing. These shifts have mostly been examined in lakes in temperate and boreal regions and within anthropogenically disturbed basins. Here, it is demonstrated that tropical floodplain lakes in a region of virtually no human disturbance naturally undergo frequent regime shifts. We demonstrate this using satellite imagery to provide a 23-year time series of 22-oxbow lakes or “cochas” along 300 km of the Manu River in SE Perú. In any year, a majority of these lakes is in a macrophyte-free, phytoplankton-dominated state. However, over the 23 years covered by images, roughly a third of the lakes experienced abrupt shifts to a floating macrophyte state. Macrophyte cover persisted for ≤ 3 year. Analysis of water level fluctuations sampled on a subset of the lakes for 1 year suggests that lake isolation from streams and the main river facilitates regime shifts. Multiple forcing factors, both internal and external to the lakes themselves, could drive the observed regime shifts, but insufficient data exist from this remote region to identify the key processes.