Adams, D. D.. Center for Earth and Environmental Science, adamsdd@splava.cc.plattsburgh.edu
Vila, I. D.. Limnological Laboratory o.dic.uchile.cl, limnolog@abello.dic.uchile.edu
Cortés, E. Comisión Centro de Estudios Nucleares, ecortes@gopher.cchen.cl
Valero-Garcés, B. L.. Consejo Superior de Investigacione Científicas, blas@ipe.csic.es
Pizarro, J. Depto. Ingenieria, jpizarro@lauca.usach.cl
Salazar, C. Direccion General de Aguas, csalazar@mop.cl

 
IMPACT OF AN EL NIÑO FLOOD ON CHILEAN RESERVOIRS CHANGES IN METHANE DIFFUSION AT THE SEDIMENT WATER INTERFACE AND CHEMICAL/GEOLOGICAL IDENTIFICATION OF LAYERS FROM PREVIOUS ENSO EVENTS
 
The geochemistry of surface sediments (0-80 cm) at two Chilean semi-arid area reservoirs, 170 to 400 km from Santiago, were investigated 4-5 times between Jan 96 and Nov 97, especially in relationship to sediment gases and processes at the sediment-water interface. Both reservoirs are 30 years old, with Rapel Reservoir built mainly for hydropower and the La Paloma for irrigation. Both reservoirs are undergoing rapid eutrophication, and Rapel experienced two large fish kills in the winters of 89 and 90. Summer hypolimnetic anoxia normally occurs near the dams. Coring revealed layers of black (possibly reducing) and brown (El Niño?) sediments having different mineralogy, grain size, chemistry and sedimentological properties. During periods of drought the surface sediments have a high water content (>80%) and contain large concentrations of methane (2-5 mM) and other reduced chemicals, such as Fe2+ and Mn2+, while El Niño floods in June 97 deposited brown, finer-grain size sediments, containing higher amounts of clay minerals with low water content (60-65%) and low pore water methane (0.02-0.2 mM). Calculated diffusive flux of methane at the sediment-water interface decreased by 100x during this period of flooding compared to the previous winter. However, within five months surface methane had increased to previous concentrations suggesting rapid anaerobic decomposition of deposited vegetative detritus.
 
Day: Thursday, Feb. 4
Time: 04:30 - 04:45pm
Location: Eldorado Hotel
 
Code: SS52TH0430E