Processos de sedimentació i distribució de radioactivitat natural i artificial en sistemes aquàtics continentals de Catalunya (Embassaments de Flix i tram català del riu Ebre, Camarasa i llacs pirinencs)

Abstract

This Doctoral thesis was carried out in 3 different Catalan aquatic ecosystems: The Flix reservoir and the lower part of Ebro river, the Camarasa reservoir (Pre-Pyrenees) and the Pyrenees lakes.<br/>The aim of this Doctoral Thesis in the Flix reservoir and the lower part of Ebro river part was to determine the Naturally Occurring Radioactivity waste materials (NORM) contained in Flix Reservoir sediments due to the dicalcium phosphate (DCP) production of a factory located in the reservoir vicinity, and evaluate the potential remobilization of the NORM waste materials downstream, along the 95 km of Ebro river until its river mouth delta (Ebro Delta). The results display an evident radiological impact in the waste materials dumped in Flix reservoir with maximum values of values 11723±198 Bq kg-1 238U, 9361± 181 Bq kg-1 226Ra, 3500±157 Bq kg-1 210Pb, 308 (238U), 92 (226Ra) and 38 (210Pb) times higher than the activity of these radionuclides in the Ebro sediments, that show an average activity of 20 Bq kg-1. In order to determine the mobilization of the radioactivity, 226Ra (dissolve) was studied. An enhancement of the 226Ra levels in water was detected in the Flix water (8.0&#61617;0.4 Bq m-3) and specially in the Flix meanders with a value of 37.5 ±1.2 Bq m-3, typical of the contaminated NORM rivers. However the rest of the lower part of the river water samples display non contaminated levels of 226Ra, with an average value of 5.9 ±1.6 Bq m-3.<br/>In Camarasa reservoir the aim of the research was to establish the sedimentation rates by 210Pb models (CFCS) and 137Cs dating mark, that allows us to date the last 100-150 years. The highest sedimentation rate in the central and lower part of the reservoir was 3.3 ± 0.2 cm yr-1 (14.1 kg m-2 a-1), close to the dam, due to the dam barrier effect that block the water stream. The central part of the reservoir displays a lower sedimentation rate of 1.37&#61617;0.14 cm yr-1. We have to take into account the effect of the flood events in the assessment of the sedimentation rates. In this study a punctual flood event in November 1982 was registered in the sediments depositing from 30 to 40 cm of material in 1 week, equivalent to 25 years of normal sedimentation in the central part of the reservoir. <br/>In the Pyrenees lake study, the distribution of 210Pb (0 to 5178 ± 1300 Bq·kg-1) and 137Cs (8 to 2970 ± 101 Bq·kg-1) displays a wide variation activity ranges, typical of remote lakes. 210Pb was used as a normalizer of the heavy metal (Zn and Cd) contaminations and some organochlorate compounds (Hexachlorobenzen and Hexachlorociclohexan) in order to detected contamination sources. The metal results display an evident Zn and Cd contamination in some lakes of Vall d'Aran area (Pica Palomera and Montoliu lakes) due to the mining activity during the period from 1740 to 1968. On the other hand, the normalized organochlorinate compounds display a source of contamination close to Sabiñanigo village (Aragon Pyrenees) probably due to the presence in the past of an Hexachlorociclohexan factory.