Historical Reconstruction of Regime Shifts in Amazon Oxbow Lakes - A Remote Sensing Approach
Abstract
Regime shifts in shallow lakes often have been associated with land-use change, increased nutrient loading and manipulation of trophic structure (Carpenter 2003). These shifts typically have been examined in lakes in temperate and boreal regions and within anthropogenically disturbed basins. By contrast in this study we examine a series of tropical floodplain lakes in a region of virtually no human disturbance to evaluate the effects of hydrological variability on ecosystem structure and dynamics. We reconstruct a timeline of regime shifts in Amazonian oxbow lakes (cochas) along the Manu River, Peru within the Manu National Park. The park contains the entire Manu watershed, including the river and oxbow lakes, providing an unprecedented opportunity to study both tropical lakes within a key region of high biodiversity, as well as regime shifts within a watershed that has not experienced any significant human influence. The Cocha Cashu Biological station was established on the banks of one of the Manu River’s oxbow lakes in the 1970 and has been operated by J. Terborgh since 1973. Observational reports from the station indicate that two types of flood events affect the floodplain lakes: “normal” floods that occur every year in the rainy season (October to May) and “megafloods” - extreme events that occur once a decade or so and sweep over the entire floodplain. Three megafloods occurred in the Manu River’s floodplain in the last 35 years: 1982, 1999 and 2003. The 2003 flood was followed rapidly by a regime shift at Cocha Cashu from phytoplankton, the state in which it had existed for the previous 30 years of observation, to a clear water lake with a luxuriant growth of submerged aquatic vegetation. Three years later in 2006, the lake switched again, this time to a state dominated by floating vegetation (Pistia stratiotes). It was not known at that time whether these changes were basin-wide and occurring at other lakes or whether they had occurred in the past. The release of the Landsat 5 archive in 2009 allows us to investigate the lakes of the Manu floodplain over the past 23 years along a 200km stretch of the river and reconstruct a timeline of regime shifts throughout the watershed. Using the Normalized Difference Vegetation Index (NDVI) we documented that Cocha Cashu is not the only lake that has undergone regime shifts in the last 23 years. Here we report on the occurrence of the shifts and analyze the relationships between dominance by surface vegetation and precipitation extremes. We also evaluate the importance of connectivity to the river, as well as the locations of the lakes in the flood plain, and how these affect the probability of being inundated by flood pulses and the probability of a major shift in ecosystem state.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H33K..04B
- Keywords:
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- 1813 HYDROLOGY / Eco-hydrology;
- 1855 HYDROLOGY / Remote sensing