Particulate metals contamination in the Kishon River estuary, Israel

Abstract

Suspended particulate matter (SPM) collected along the axis of the Kishon River, its estuary and Haifa Bay were analysed for trace metal concentrations together with measurements of water density, pH and dissolved oxygen. The concentrations of particulate Cd, Zn and Cu generally increased from the upper Kishon system (upstream from Tzipori-Kishon Junction) downstream and decreased from the Kishon Harbour seaward, while particulate Al concentrations decreased downstream and towards the open sea. Enrichment of Cd, Zn and Cu was found at Haifa Bay compared to the upper Kishon system. The axial profile of Mn concentrations indicated reduction of Mn at the anoxic and low pH zone of the lower river system and precipitation of Mnoxides at the estuary in response to the increase in pH and dissolved oxygen concentrations. Although Fe concentrations showed similar behavior to that of Al, the higher Fe Al ratios at the estuary are probably due to precipitation of Fe-oxides onto pre-existing particles. This spatial non-conservative behavior of metals is presumably due to the: 1. mixing between polluted river-borne particles and material of drainage basin and coastal origin; 2. changes of the distribution coefficient of metals between the particulate and solution phases (K d) with variations of salinity, pH and SPM concentrations; and 3. physical settling and currents. Short-term, tidal cycle measurements undertaken at the lower Kishon system (Julius Simon Bridge) indicated a high contribution of resuspended sediments to the SPM amounts due to the high tidal energy. It is hypothesized that the latter is the main mechanism by which SPM, which settles in the estuary, is transported landward creating a turbidity maximum zone between the Julius Simon and Histadrut bridges, i.e. about 3 km upstream from the estuary. It is proposed that the upper estuary zone acts as a purging system through which a low flux of SPM, enriched by organic and trace metal content, is transported seaward and from which a high flux of SPM is returned landward due to tidal stress.