Occurrence, source identification and ecological risk assessment of heavy metals in water and sediments of Uchalli lake - Ramsar site, Pakistan

Abstract

Uchalli Lake is an internationally significant Ramsar site that needs protection for supporting migratory birds. The current study aimed to assess wetland health by examining water and sediments utilizing total and labile heavy metals concentration, pollution indices, ecological risk assessment, water recharge and pollution induction sources through isotope tracer techniques. Al concentration in water was of serious concern as it was 440 times higher than the maximum acceptable concentration of Environmental Quality Standard of the UK for aquatic life in saline waters. Labile concentration predicted very severe enrichment of Cd, Pb, and moderate enrichment of Cu. Modified ecological risk index predicted very high ecological risk in sediments. The δ ¹⁸O, δ²H and D-excess values indicate that the lake was mainly recharged by local meteoric water. Enriched values of δ ¹⁸O and δ²H suggest a high evaporation of lake water, making lake sediments more enriched with metals. Isotopic and D-excess values of groundwater suggest a quick rainwater recharge to groundwater around the Uchalli Lake. Nitrates isotopes indicate that the rainwater runoff is main source of induction of fertilizers, pesticides and soil bonded metals in the lake system. The lake is recharged by rainwater runoff, from catchment areas, that erode the soil particles and agricultural residual waste dumped in the lake.

Keywords: Ecological risk assessment; Heavy metals; Metal induction sources; Pollution indices; Stable isotopes; Uchalli wetland (Pakistan).