Short communicationInfluence of the hierarchical structure of land use on metals, nutrients and organochlorine pesticides in urban river sediments
Introduction
Urban waterways play a significant role in enhancing urban liveability. However, safeguarding the health of these water ecosystems is challenging due to ever increasing urban population and the spread of the urban footprint (Everard and Moggridge, 2012; Wen et al., 2017). In this context, land use plays a key role as urbanisation transforms natural lands into a range of different urban uses, which generate a diversity of pollutants that are transported by stormwater runoff and wastewater discharge, into waterways (Anim et al., 2017; Borrelli et al., 2017; Liu et al., 2017a; Liu et al., 2017c). Some of these pollutants settle in river sediments and continue to interact with the water column, posing long-term risks to the aquatic environment, and in turn, human health (Wijesiri et al., 2019b).
Metals, nutrients and pesticides are amongst the pollutants commonly present in urban waterway sediments (Duodu et al., 2016a, Duodu et al., 2017; Wijesiri et al., 2019a). These are generated either directly by various land use related anthropogenic activities, or present in the urban environment as legacy pollutants. For example, organochlorine pesticides (OCPs) have been banned or subjected to restricted use for decades, but the residual amounts still remain in the environment (Li et al., 2008).
Past research has commonly investigated only the impacts of primary land uses on sediment quality. As Liu et al. (2017b) noted, the primary level of land use disaggregation is inadequate for in-depth understanding of the influence of land use on river sediment pollution. The subdivision to a secondary level at the minimum, is the logical approach, because there can be a variety of land uses that could generate different types and quantities of pollutants. However, investigations into sediment pollution using secondary level land use data is constrained by the lack of information on detailed land use distribution.
This study is an extension of the initial research undertaken by Liu et al., 2017a, Liu et al., 2017b to assess the extent to which primary and secondary levels of land uses can be determinants of potential sources of pollutants in urban river sediments. It was hypothesised that higher levels of land use demarcation can generate more reliable information about pollutant sources. The research outcomes will contribute to advancing land use management strategies, and thereby help to improve the quality of receiving water bodies.
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Study sites and land use data
Sediment sampling was undertaken in Shenzhen River, China (11 sites, Fig. 1a) and Brisbane River, Australia (21 sites, Fig. 1b), encompassing upstream, middle and downstream reaches. The two rivers flow through areas with different urbanisation characteristics (refer to Table S1 in Supporting Information).
The land use data was obtained from a spatial database using ArcGIS software. Although primary land uses could be identified for both rivers, the secondary level land uses could only be
Pollutant distribution in river sediments
The results showed that the concentrations of total human-sourced metals in Shenzhen River are higher compared to the Brisbane River (see Table S5 in the Supporting Information), which is consistent with the results reported elsewhere, for example, Ganga River, India (Pandey and Singh, 2017), Euphrates River, Iraq (Salah et al., 2012), Yangtze River, China (Wang et al., 2011) and Buriganga River, Bangladesh (Saha and Hossain, 2011). While total soil-sourced metals concentrations in both rivers
Conclusions
This study investigated the need for disaggregated levels of land use data for in-depth understanding of the relationship between land use and river sediment pollution. The concentrations of metals, nutrients and OCPs were found to be consistent with past studies. It was found that the sole reliance on primary level of land uses is inadequate for identifying potential pollutant sources, and the secondary level of land uses is a substantially better determinant of pollutant sources. The study
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
Authors thank Guangdong Basic and Applied Basic Research Foundation, China (2019A1515110353, 2019A1515010843) and Key-Area Research and Development Program of Guangdong Province (2019B110205003) for the financial support.
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