Temporal and spatial variations of heavy metals in urban riverine sediment: An example of Shenzhen River, Pearl River Delta, China Yilong Huang a, b, * , Wenbo Zhu b , Maohua Le b , Xixi Lu a a Department of Geography, National University of Singapore, Singapore 119260, Singapore b Shenzhen Water Planning and Design Institute, The Bureau of Water Resource Management for Shenzhen Ministry, Shenzhen 518036, Guangdong Province, PR China article info Article history: Available online 12 June 2011 abstract Heavy metal contamination has great ecological risk for river ecosystems due to its environmental toxicity, abundance and persistence. The examination and study of sediment quality can reveal the pollutant variations, degradations, cycles and chronic effects of water pollution. In this study, surface (0e60 mm) river sediment samples were collected and heavy metals (Cr, Cd, Hg, As, Zn, Cu and Pb) were analyzed in order to understand the spatial and temporal variation of heavy metals and its potential ecological risk in the Shenzhen River during 1991e2006. Cr showed a significant increasing trend (P < 0.05), while both As and Cd increased but not with statistical significance (P ¼ 0.10) over time. A slightly increasing trend was found for Hg and Zn, but Pb and Cu showed no trend over time. Risk index (RI) ranged from 194.8 to 1417.6 in sediment, indicating considerable ecological risk or very high ecological risk for the aquatic environment. Among the 7 heavy metals, Cd and Hg were the major contributing (83%) elements for RI. Concentrations of heavy metals in sediment also have significant variations on spatial scale, high in industrialized and urbanized areas (Buji catchment, Futian catchment and Paihong catchment). RI ranged from 540.2 to 2876.8 for the 18 plots, and Cd was the major contributing heavy element (55.1e99.1%). The sediments of Shenzhen River all showed considerable ecological risk or very high ecological risk in 2004. Ó 2011 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The sediments deposited on river bed are important material as river habitats and for ecosystems (Sin et al., 2001). However, river conditions have declined with expanding industrial activities and the related population growth in urbanized catchments (Marshall et al., 2010; Yuan et al., 2011). River sediment is an important sink of heavy metals, but also is a secondary contamination source affecting the health of river ecosystems (Fan et al., 2002; Wang et al., 2010). Extraction and disturbance processes altering redux potential of sediments and chemical forms of heavy metals can accelerate release of heavy metals from sediments to water and organisms (Gambrell, 1994; Zhuang et al., 1994; Fan et al., 2002; Strady et al., 2011). Heavy metal contamination in river ecosys- tems has attracted attention in recent years due to its environ- mental toxicity, abundance and persistence (Sin et al., 2001; Armitage et al., 2007; Yuan et al., 2011). Thus, it is important to determine the intensity of pollution by inventorying the heavy metal concentrations and their spatial distribution in a river system (Audry et al., 2004). Heavy metals can enter the river through many pathways, including disposal of liquid effluents, terrestrial runoff, and leach- ates carrying chemicals originating from numerous urban, indus- trial, and agricultural activities, as well as atmospheric deposition (Karageorgis et al., 2002; Mucha et al., 2003; Pekey et al., 2004; Bai et al., 2011). After entering a river, heavy metals are rapidly removed from the water body and absorbed by fine sediment particles (Tam and Wong, 2000). Although the concentrations of heavy metals in aquatic phases are often low, the contents in sediments can be high (Ferreira et al., 1996) with obvious distri- bution patterns (Batley, 1989). Riverine sediments have been recognized as sensitive indicators for monitoring contaminants (Ergin et al., 1991; Balls et al., 1997; Atgin et al., 2000). The exam- ination and study of sediment quality can reveal pollutant varia- tions, degradations, cycles, and chronic effects of water pollution (Ferreira et al., 1996). Therefore, it is useful to assess the contami- nation characteristics and ecological risk through evaluation of the total metal contents in sediment (Hua et al., 2011). Several methods, including index of geo accumulation (I geo ), pollution load * Corresponding author. Department of Geography, National University of Singapore, Singapore 119260, Singapore. E-mail address: geohy@nus.edu.sg (Y. Huang). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ e see front matter Ó 2011 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2011.05.026 Quaternary International 282 (2012) 145e151