Metals content in sediments of ephemeral streams with small reservoirs (the Negev Desert)

The content of 19 metals (chromium, cobalt, nickel, strontium, arsenic, magnesium, barium, cesium, gallium, rubidium, uranium, vanadium, zinc, lead, copper, cadmium, iron, manganese, and aluminum) in sediment in three ephemeral streams (Nahal Sansana, Nahal Revivim and Nahal Pura) with reservoirs in the Negev Desert is studied herein. The study was done in September 2016. The samples were collected from the surface layer of sediment (up to 10 cm) in the reservoirs and in the channels upstream and downstream of the reservoirs. Silt, which on average, accounted for 72% dominated in the sediment. In the spatial distribution of the particle size, sand and gravel fractions were deposited in the reservoirs. Aluminum, iron, and magnesium accounted for 99% of all analyzed metals. The Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) showed that sediment in the Negev Desert channel upstream of the reservoirs had similar concentrations of metals. Similarities were also found between the analyzed reservoirs. The bottom sediment in reservoirs had higher concentrations of metals than sediment upstream and downstream of the reservoirs. The comparison of concentrations in upstream and downstream locations did not show any unambiguous trends because metal concentrations downstream from the reservoirs were not always lower than upstream of the reservoirs. The analysis of the sediment enrichment factor (EF) showed the highest value in the reservoirs and the lowest downstream of the reservoirs. The concentrations of most analyzed metals did not indicate the possibility of potential ecological risk (SQG).