Heavy metal gradients from rural to urban lakes in central China

Background Limited information is available on heavy metal patterns in lakes under rapid watershed urbanization, especially considering a large spatial gradient with a long linear distance and great variations in topographic relief. To fill this gap, we studied concentrations of a series of heavy metals in both water and sediments from 20 lakes along a rural to urban gradient in central China, and we aimed to understand the effects of urban processes on heavy metal dynamics in lake ecosystems. Studied lakes were divided into five groups: A (rural reservoir group), B (rural commercial fishing group), C (urban park group), D (urban recreational fishing group), and E (urban commercial fishing group). An inductively coupled plasma optical emission spectrometer (ICP-OES) and an inductively coupled plasma-mass spectrometer (ICP-MS) were used to analyze the heavy metals in water and sediments. Results An increasing trend of most heavy metals in water from rural to urban lakes was observed. Concentrations of cadmium (Cd), cobalt (Co), lead (Pb), chromium (Cr), arsenic (As), nickel (Ni), magnesium (Mn), iron (Fe), and aluminum (Al) in water were significantly lower in rural group A than those in other groups. Arsenic in sediments of rural group A was lower than those in other groups. No other heavy metal element in sediments was significantly different among groups. The enrichment factor analysis of selected heavy metals showed there were different degrees of enrichments of heavy metals in sediments. The potential ecological risk index showed a low level for heavy metals in sediments of all studied lakes. Conclusions Results indicated that urban processes could have an impact on heavy metals in lake water. The sources of heavy metals in sediments were more likely from anthropogenic activities. These results could enhance our understanding of metal dynamics in lake ecosystems under urbanization and could help prevent heavy metal pollutions and promote sustainable management of urban ecosystems.