Mid term variation of vertical distribution of Acid Volatile Sulphide and Simultaneously Extracted Metals in sediment cores from Lake Albufera (Valencia, Spain)

Abstract

Lake Albufera is one of the most eutrophic bodies of water in Spain due to the point and diffuse pollution over past decades and its sediments are likely to be anoxic because of the high organic matter flux. Hence, sulphides can play an important role in limiting the mobility of heavy metals. This work aimed to study the vertical variation of acid volatile sulphide (AVS) and simultaneously extracted metals (SEM) in sediment cores collected from Lake Albufera; other sediment characteristics like organic matter, biochemical oxygen demand or total metals were also studied. Three sites were selected and four sampling campaigns were carried out in order to study the spatial and temporal variation, as well as to obtain information regarding the historical variation in the composition of sediments. AVS and SEM were analysed by the purge and trap method. The vertical distribution of AVS and SEM varied depending on the sampling site, concentrations of AVS and SEM were higher at sites close to mouths of inflowing channels. A decreasing trend of AVS has been found at these sites over time: in the two first samplings, AVS increased with depth reaching maximum concentrations of 40 and 21 µmol g-1, but from then on, AVS were lower and decreased with depth. SEM decreased with depth from 3 µmol g-1 in surface layers to around 1 µmol g-1 at deeper segments at these sites. However, the central site was more uniform with depth as well as with time, presenting lower values of SEM and AVS (mean of 0.9 and 2.0 µmol g-1 respectively); there the maximum value of AVS (7 µmol g-1) was found at the top layer (0-3 cm). According to the (SEM-AVS)/fOC approach every sites, and throughout the whole cores, can be classified as non-toxic respect metals, as the values were under 130 µmol g-1.