The off-site implications of deforestation on sedimentation rates and pollution in Abkenar open water (Anzali Lagoon, Caspian Sea) using radionuclide techniques and sediment quality indices

Abstract

Abkenar open water (AOW) has a 35 km2 distribution and is the largest part of the Anzali Lagoon in the southern coastal zone of the Caspian Sea. The effects of deforestation in the upstream basin of the AOW were assessed by measuring the rate of sedimentation, sediment contamination, and ecological risk for aquatic life and end-users using radioisotopes Cesium-137 and Lead-210. The chronology of the AOW sediment column was studied using the Constant Rate of Supply model. Correlations between environmental changes and the sedimentary regime of the study area highlight the contribution of the AOW authorized international and local wood harvesting companies pre-and-post 1950 in the catchment in terms of the rate of sediment supply and the influx of toxic metals. Historical evidence shows that two specific layers formed during World Wars I and II with the mean rates of 0.185 ± 0.04 (±STD) and 0.32 ± 0.02 kg/(m·y), respectively. The highest influx of alkali elements and toxic metals (nickel, cadmium, lead, zinc, and copper) into the basin occurred in 1945. Two layers of gray mud (16–50 cm) and organic-rich dark loss mud (0–16 cm) correlated well with the programmed wood harvesting projects. These layers accumulated from 1953 to 2000 with a mean rate of 0.6 ± 0.2 and 2 ± 0.7 kg/(m2·y). Thus, aquatic life and end-users have been exposed to moderate to extremely high levels of toxic metals and a moderate level of contamination since the 1950s.