title: Sediment size distribution and composition in a reservoir affected by severe water level fluctuations.
abstract: The reservoir sediments are important sinks for organic carbon (OC), the OC burial being dependent on two opposite processes, deposition and mineralization. Hence factors such as severe water level fluctuations are expected to influence the rate of OC accumulation as they may affect both deposition and mineralization. The Barasona Reservoir has been historically threatened by siltation, whilst the use of water for irrigation involves a drastic decrease of the water level. In this context, we have studied the physical and chemical characteristics (grain size, major and minor elemental compositions, organic and inorganic carbon, and nitrogen) of the recent sediments of the Barasona Reservoir and the relationships among them in order to: a) elucidate the main processes governing OC accumulation, b) evaluate the rate of OC mineralization and c) approach the effect of drought on the sediment characteristics in this system. Our results indicated that Barasona sediments were dominated by fine silts (>60%) and clays (>20%), the mean particle size decreasing from tail to dam. Desiccation increased particle sorting and size distribution became bimodal, but no effect on average size was observed. Attending to the composition, Barasona sediments were very homogeneous with low concentrations of nitrogen (TN) and phosphorus (<1.2 g kg(-1) dw and <0.6 g kg(-1) dw, respectively) and high concentration of OC (≈36 g kg(-1) dw). TN was negatively related to dry weight. Sediment mixing due to drastic changes in water level may have favoured the observed homogeneity of Barasona sediments affecting carbon, major ions and grain size. The high amount of OC deposited in Barasona sediment suggested that the adsorption of OC onto fine particles was more important than in boreal lakes. The rate of oxygen consumption by wet sediment ranged from 2.26 to 3.15 mg O2 m(-2) day(-1), values close to those compiled for Mediterranean running waters.
authors.affiliation: Department of Ecology, Faculty of Biology, University of Barcelona, Barcelona, Spain. Electronic address: marilopez@ub.edu.
authors.forename: Pilar
authors.initials: P
authors.lastname: López
authors.affiliation: Institute of Earth and Environmental Science, University of Potsdam, Germany; School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, UK; Fluvial Dynamics Research Group, Department of Environment and Soil Sciences, University of Lleida, Lleida, Spain.
authors.forename: José A
authors.initials: JA
authors.lastname: López-Tarazón
authors.affiliation: Catalan Institute for Water Research, (ICRA), Girona, Catalonia, Spain.
authors.forename: Joan P
authors.initials: JP
authors.lastname: Casas-Ruiz
authors.affiliation: Department of Ecology, Faculty of Biology, University of Barcelona, Barcelona, Spain; Department of Ecology, Institute of Biology, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Pompeo
authors.affiliation: Department of Ecology, Faculty of Biology, University of Barcelona, Barcelona, Spain.
authors.forename: Jaime
authors.initials: J
authors.lastname: Ordoñez
authors.affiliation: Department of Ecology, Faculty of Biology, University of Barcelona, Barcelona, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Muñoz
keywords: Barasona reservoir; Drought; Grain-size; Organic carbon; Respiration rate; Sediment