Spatial-temporal-biological accumulation effect and its potential ecological risk of five heavy metals in an urban wetland of plateau region

Abstract

Wetlands are facing enormous ecological risk at the same time of absorbing and accumulating heavy metals through the physical, chemical and biological processes. This study focuses on the heavy metal accumulation effect (AE) and its potential ecological risk (PER) of the Houshaogou urban cascade constructed wetland, located in the Xining City of Qinghai Province in China. By using the geoaccumulation index (Igeo) conjoint with PER index (E), the current study analyzed AE and PER of five kinds of common heavy metals (Cd, Cr, Pb, As and Zn) in spatial, temporal and biological three scale. Results showed that three kinds of heavy metals (Cd, Cr and Zn) exhibited different levels of AE (0 < Igeo < 5) in sediments and organisms, which posed different levels of ecological risk for both natural ecosystems and humans. In spatial scale, the AE of Cd, Cr and Zn gradually increased from upstream wetlands to downstream wetlands. Heavy metals Cr and Zn, except for Cd, are at low level of PER (E<40) in wetland sediments. In temporal scale, Cd, Cr and Zn presented accumulation effects (0 < Igeo < 2) in all three studied periods. Considerable PER was triggered by Cd (80≤ECd<160) in sediments from 2013-2016. In biologically scale, Cd presented a higher level of AE (1< Igeo < 5) in organisms, leading to a higher level of risk ranges from considerable PER (80≤E<160) to very high PER (E≥320). The current study may provide information of heavy metal accumulation and removal processes of the Huoshaogou constructed wetland, which is important for sustainable ecological management and ecological risk regulation of urban wetlands.