Labile trace metal contribution of the runoff collector to a semi-urban river

Abstract

In this study, the distribution of labile trace metals (LTMs; Cd, Co, Cr, Cu, Ni, Pb, and Zn) in a semi-urban runoff collector was examined to assess its influence to a natural aqueous system (Jalle River, Bordeaux, France). This river is of high importance as it is part of a natural reserve dedicated to conserving aquatic flora and fauna. Two sampling campaigns with a differing precipitation condition (period 1, spring season; and period 2, summer season associated with storms) were considered. Precipitation and water flow were monitored. The collector is active as it is receptive to precipitation changes. It influences the river through discharging water, contributing LTMs, and channeling the mass fluxes. During period 2 where precipitation rate is higher, 25 % of the total water volume of the river was supplied by the collector. LTMs were detected at the collector. Measurements were done by using diffusive gradient in thin films (DGT) probes deployed during 1, 7, and 14 days in each period. The results showed that in an instantaneous period (day 1 or D1), most of these trace metals are above the environmental quality standards (Cd, Co, Cr, and Zn). The coefficient of determination (r (2) > 0.50) employed confirmed that the LTM concentrations in the downstream can be explained by the collector. While Co and Cr are from the upstream and the collector, Cd, Cu, and Zn are mostly provided by the collector. Ni, however, is mostly delivered by the upstream. Using the concentrations observed, the river can be affected by the collector in varying ways: (1) adding effect, resulting from the mix of the upstream and the collector (if upstream ˂ downstream); (2) diluted (if upstream ˃ downstream); and (3) conservative or unaffected (upstream ~ downstream). The range of LTM mass fluxes that the collector holds are as follows: (1) limited range or ˂10 g/day, Cd (0.04-1.75 g/day), Co (0.08-05.42 g/day), Ni (0.06-1.45 g/day), and Pb (0.08-9.89 g/day); (2) moderate range or 11-50 g/day, Cr (0.23-33.26 g/day) and Cu (0.77-37.88 g/day); and (3) wide range or ˃50 g/day, Zn (26.33-676.61 g/day). Hence, the collector is a major source of concern in terms of contamination. This is as the water with considerable LTMs is channeled openly to the river without any treatment.

The Long-Term Effects of Dredging on Chromium Pollution in the Sediment of Meiliang Bay, Lake Taihu, China

“…Storm water runoff is recognized as the main mechanism of transportation of external heavy metals into fluvial system [28]. The seasonal change in external Cr source could be mainly affected by rainfall.…”

Spatial-temporal variability and influence factors of Cd in soils of Guangxi, China

“…Precipitation also affects the migration and transport of heavy metals in the soil [ 67 ]. As the intensity and frequency of precipitation increases, the leaching of heavy metals from the soil increases, and these leached heavy metals enter the river system or infiltrate into groundwater [ 68 ]. Therefore, the negative correlation between precipitation and spatial variation of Cd may be related to the leaching effect.…”

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“…Hence, in general concentration can be expected low. Intensity and frequency of the occurrence of rainfall have impact on the concentration of an element or molecule [11]. The highest concentration in the collector during the 1 st sampling campaign and at the center of 6-meter-deep during the 2 nd sampling should be further investigated.…”