Historical Change and Ecological Risk of Potentially Toxic Elements in the Lake Sediments from North Aral Sea, Central Asia

Abstract

The Aral Sea has received worldwide attention for the deterioration of its biological and chemical status. The accumulation of potentially toxic elements (PTEs) in the lake sediments reflects changes in the surrounding watershed and represents a potential hazard for the lake ecosystem. In conjunction with existing environmental records from the Aral Sea basin, sedimentary records of PTEs in North Aral Sea covering a short time scale, anno Domini (AD) 1950–2018, were used to reveal historical changes in PTE concentrations and potential risks to lake functioning. The results suggested that the levels of PTEs in lake sediments from North Aral Sea changed abruptly around 1970 AD, which is concurrent with the intensification of human activities within the basin. After 1970 AD, with the exception of As, which remained at unpolluted-to-moderately polluted levels, the geo-accumulation indices of the remaining PTEs studied (V, Cr, Zn, Co, Pb, Ni, Cu and Cd) inferred a moderately polluted status. Before 1970 AD, the total ecological risk was low, but since 1970, the total ecological risk index has exceeded 150, indicating moderate risk. Historical changes in PTE levels of lake sediments from North Aral Sea and their potential ecological risks are reported for the first time. The conclusions provide an important reference for the protection of lake ecosystems and will provide data for regional/global comparisons of environmental change during the Anthropocene.

Organic Carbon Burial in the Aral Sea of Central Asia

“…Sub-samples were taken at 1-cm intervals on site, sealed, and stored in plastic bags for dating and analysis of the environmental proxy indicators. The specific activity of 137 Cs was used to determine the age of the sedimentary strata, the activity was measured, and the depth-age model was based on the former published literature [16].…”

“…In the context of global warming, the increase in microbial respiration and the mineralization rate of organic matter in water bodies and sediments may lead to a decline in the rate of organic carbon burial, and sediments may change from "carbon sink" to "carbon source" [13]. Many studies have shown that, with the increasing intensity of human activities, lake environments and ecosystems have experienced significant changes [14][15][16], and in-depth study of the temporal and spatial changes of organic carbon burial in lake sediments and their relationship with lake ecology, climate environment, and human activities will not only help to understand the evolution of the lake ecological environment more deeply but also make it possible to more scientifically assess the role of lake organic carbon burial in the global carbon cycle.…”

“…The research on lake sediments has become more abundant, e.g., environmental reconstructions of the salt water, geological structure, etc. through biological indicators [33][34][35]; the use of sedimentary records of titanium changes to restore the wind intensity and frequency characteristics of western Central Asia since the Late Holocene [36]; the ecological risk assessment of potentially toxic elements in the North Aral Sea [16]; etc.…”

Viral Community Structure and Potential Functions in the Dried-Out Aral Sea Basin Change along a Desiccation Gradient

“…The desertification of the Aral Sea basin in Uzbekistan and Kazakhstan is considered one of the most catastrophic environmental disasters of the last century ( 1 ). At present, the man-made terrestrial desert is characterized by distinct extremophilic conditions as well as the accumulation of various hazardous substances and heavy metals, i.e., Pb, Ni, Cu, and Cd ( 1 – 4 ). Over the past 40 years, the dried-out Aral Sea basin has undergone major changes, including a primary succession of halophilic plants ( 5 ).…”

Function-Based Rhizosphere Assembly along a Gradient of Desiccation in the Former Aral Sea

“…Since the 1960s, the world’s fourth-largest inland body of water has been, due to unsustainable expansion of intense, irrigated plant production, especially cotton, under arid conditions, continuously shrinking, which has resulted in an extreme increase of salinity up to 100 g L −1 ( 1 – 3 ). In parallel, many hazardous and carcinogenic substances, as well as heavy metals, i.e., Pb, Ni, Cu, and Cd, mainly originating from agricultural effluents and pesticide residues, were deposited in the Aral Sea basin ( 4 – 6 ). Now, these sediments with enriched toxins form carcinogenic salt dust storms that negatively impact environmental as well as human health ( 1 ).…”