Potentially toxic metals in sediments, lake water and groundwater of the Ramsar wetlands Bakhtegan–Tashk, South Iran: Distribution and source assessment

Abstract

Bakhtegan–TashkLakes (BTL) and Kamjan Marsh, one of the Ramsar sites with an area of 1323 km 2 , have been shrunk due to groundwater overexploitation, construction of two new dams and drought. Evaporation of the BTL water significantly increased potentially toxic metal (PTMs) and average total dissolved solids (TDS) from 45000 to 382000 mg/l. This study focuses on contamination and sources of 16 PTMs. The sampling sites include 24 sediments, 2 surface salts, 17 water samples from Bakhtegan Lake (BL), and two wells. The PTMs were analyzed in Act Lab. The BTL sediments are contaminated by Hg, Ni, Mo and Se based on CF, EF, I geo indices and at ecological risks by Hg, Ni and Cr based on SQGs index and by Hg based on ecological Risk index. Kamjan Marsh and adjacent aquifer were at negligible ecological risk. Most PTMs concentrations in water samples were not measured due to dilution. The BL water and groundwater below the BL bed were contaminated and/or at ecological risk by significantly high values of TDS and measurable PTMs Mo, Pb, V, As, Mn and Sb. The most probable sources of contamination are chromite mines, sewage of petrochemical and industrial complexes, contaminated dust from west of Iran and Iraq, combustion of fossil fuel and fertilizers. The BTL can be restored by a new water resource plan to save water by installing water meters on all exploited wells, modern irrigation systems, optimizing crop patterns, enhancement crop yield per unit of applied water, and stakeholder cooperation. • The BTL has shrunk in recent decades, resulting in enhancement of TDS and PTMs. • The BTL sediments and water are contaminated for irrigation and aquatic life. • Hg, Mo, Se, Ni, Cr and As are the main sediment contaminants in parts of the BTL. • The BTL contaminations originate from mixed geogenic and anthropogenic sources. • The BTL can be restored by a new water resources plan with water-saving strategies.