Article Info Received : 13.07.2014 Accepted : 22.11.2014 Bulk elements and grain sizes in sediments collected at upstream and downstream of Manwan Dam were studied to demonstrate the spatial distribution of heavy metals in the sediments and to assess their risk. Correlation analysis showed that the spatial distribution of Cd, Zn and Mg were significantly affected by dam construction. PCA analysis demonstrate that Cd and Zn were both controlled by Ca, As, Pb, organic matter and clay. Mg was controlled by silt, Al, P and K. The risk assessment demonstrated that the pollution of Cd, As, Zn were more serious than other heavy metals. Fine-grained sediments with higher risk level were found in the section near the upstream of dam, while coarse-grained ones with lower risk level were found in the section far away from the downstream of dam. The sections in tributary were lower in risk than those in the main stream. Heavy metal concentrations in the mainstream sediments were influenced by dam construction and those in tributary were influenced by both dam construction and human activities in locality. Unusual high concentrations of Cd, As, and Zn in both sections implied that more pollution prevention measures are needed in the Manwan Dam in order to prevent increased heavy metal pollutions in the Lancang-Mekong River.
Purpose Dam construction alters hydrological conditions, impacting the sedimentary environment in the reservoir and modifying the regional flow of carbon. This study examined the spatial and seasonal dynamics of organic carbon in sizefractioned sediments to identify the role of physical protection (e.g. burial, aggregation) for preserving carbon and the potential impact of a dam on the mineralization of sedimentary organic carbon in the dammed Lancang-Mekong River. Materials and methods Sediment samples were collected from the Manwan Reservoir, China, in the rainy and dry seasons using a gravitational bottom sampler. One sample was collected from the centre of the river and two samples were collected on the river edges, 5 m away from each bank. Sediments were divided into three size classes of waterstable aggregates by wet sieving, including macroaggregates, microaggregates and silts. The total organic carbon (TOC), labile organic carbon (LOC), total nitrogen (TN) and stable carbon isotope (δ 13 C) were measured to analyse the dynamic features of organic carbon in the sediments. Results and discussion The preservation of organic carbon in the sediments collected from the main stream decreased with an increase in distance from the Manwan dam, while it remained consistently high in the tributaries. The majority of the sediments collected during the rainy season preserved more TOC and TN than the samples collected during the dry season. Because of the increase in the proportion of sands in macroaggregates and microaggregates, the TOC contents decreased. In contrast, silts and clays were not affected and performed well in protecting organic carbon. The sediments in the lacustrine area and forepart of the transition area, with lower δ 13 C and higher C/N values, suggested a mixture of aquatic and agro-ecosystem inputs and led to high proportions of LOC in TOC. Conclusions Dam construction reinforced the carbon sink and role of physical protection in the Manwan reservoir by enhancing fine fraction deposition and organic carbon inputs, especially during the rainy season. The sediments dominated by silts and clays absorbed and preserved more organic carbon than the samples dominated by sands. The majority of the organic carbon buried in the lacustrine area, the forepart of the transition area and the tributaries was protected by microaggregates, silts and clays. With the development of fisheries and agriculture, increasing amounts of labile organic carbon buried in sediments may lead to an increase in the potential for carbon mineralization.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.