Pb-210 And Cs-137 As Tracers Of Recent Sedimentary Processes In Two Water Reservoirs In Cuba

Hanabanilla and Paso Bonito Reservoirs are the main fresh water sources for about half a million inhabitants in central Cuba. Prior to this investigation precise information about the losses of storage capacity was not available. Sedimentation is the dominant process leading to reduction in water storage capacity. We investigated the sedimentation process in both reservoirs by analyzing environmental radionuclides (e.g. Pb-210, Ra-226 and Cs-137) in sediment cores. In the shallow Paso Bonito Reservoir (mean depth of 6.5 m; water volume of 8 X 10(6) m(3)), we estimated a mean mass accumulation rate (MAR) of 0.4 +/- 0.1 g cm(-2)y(-1) based on Pb-210 chronologies. Cs-137 was detected in the sediments, but due to the recent construction of this reservoir (1975), it was not possible to use it to validate the Pb-210 chronologies. The estimated MAR in this reservoir is higher than the typical values reported in similar shallow fresh water reservoirs worldwide. Our results highlight a significant loss of water storage capacity during the past 30 years. In the deeper and larger Hanabanilla Reservoir (mean depth of 15.5 m; water volume of 292 X 10(6) m(3)), the MAR was investigated in three different sites of the reservoir. The mean MARs based on the Pb-210 chronologies varied between 0.15 and 0.24 g cm(-2)y(-1). The MARs calculated based on the Cs-137 profiles further validated these values. We show that the sediment accumulation did not change significantly over the last 50 years. A simple empirical mixing and sedimentation model that assumes Cs-137 in the water originated from both, direct atmospheric fallout and the catchment area, was applied to interpret the Cs-137 depth profiles. The model consistently reproduced the measured Cs-137 profiles in the three cores (R-2 > 0.9). Mean residence times for Cs-137 in the water and in the catchment area of 1 y and 3550 y, respectively were estimated. The model identified areas where the catchment component was higher, zones with higher erosion in the catchment, and sites where the fallout component was quantitatively recorded in the sediments. (C) 2017 Elsevier Ltd. All rights reserved.