The reservoir sediments are important sinks for organic carbon (OC), the OC burial being dependent on two opposite
processes, deposition andmineralization. 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 ofwater 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 (N60%) and clays (N20%), 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
(b1.2 g kg−1 dw and b0.6 g kg−1dw, 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.