Significance of floods in metal dynamics and export in a small agricultural catchment

Abstract

International audienceHigh-resolution monitoring of water discharge and water sampling were performed between early October 2006 and late September 2007 in the Montoussé River, a permanent stream draining an experimental agricultural catchment in Gascogne region (SW France). Dissolved and particulate concentrations of major elements and trace metals (i.e. Al, Fe, Mn, As, Cd, Cr, Cu, Ni, Pb, Sc and Zn) were examined. Our results showed that contamination levels were deficient to moderate, as a result of sustainable agricultural practices. Regarding dynamics, metal partitioning between particulate and dissolved phases was altered during flood conditions: the particulate phase was diluted by coarser and less contaminated particles from river bottom and banks, whereas the liquid phase was rapidly enriched owing to desorption mechanisms. Soluble/reactive elements were washed-off from soils at the beginning of the rain episode. The contribution of the flood event of May 2007 (by far the most significant episode over the study period) to the annual metal export was considerable for particulate forms (72-82%) and moderate for dissolved elements (0-20%). The hydrological functioning of the Montoussé stream poses dual threat on ecosystems, the consequences of which differ from both temporal and spatial scales: (i) desorption processes at the beginning of floods induce locally a rapid enrichment (up to 3.4-fold the pre-flood signatures on average for the event of May 2007) of waters in bioavailable metals, and (ii) labile metals - enriched by anthropogenic sources - associated to particles (mainly via carbonates and Fe/Mn oxides), were predominantly transferred during floods into downstream-connected rivers

Trace element fluxes in sediments of an environmentally impacted river from a coastal zone of Brazil

“…However, the same correlation was not observed for Mn, Cd, and Zn. This behavior was also observed by Roussiez et al (2013) who showed that particulate metals (except for Cd and Mn) usually depict a strong correlation with Fe. Not surprisingly, neither the bedload nor the bedload/suspended sediment ratio was correlated with the metal concentration in this fraction.…”

Influence of anthropogenic inputs and a high-magnitude flood event on metal contamination pattern in surface bottom sediments from the Deba River urban catchment

“…5 shows the results of metal enrichment factors (EFs) for all locations considered in the two years. There is no general consensus concerning threshold of natural variability but some authors (Hernandez et al, 2003;Roussiez et al, 2013) have suggested that EF N 2 is indicative of a probable anthropogenic influence. Taking this threshold as a reference, it can clearly be seen from these plots that median EF values of Pb (b 1.2) and Mn (b0.9) are below this limit.…”

“…Variations in water and sediment physicochemical conditions could therefore play an important role in their mobilisation in the dissolved phase, where they become more bioavailable and disclose toxic chemical forms (Eggleton and Thomas, 2004;Roussiez et al, 2013).…”

Copper in soil fractions and runoff in a vineyard catchment: Insights from copper stable isotopes

“…The SPM-bound Cu was found to be isotopically lighter compared to the dissolved Cu, which may be related to isotopically heavier Cu associated with DOM in the dissolved phase (El Azzi et al, 2013;Vance et al, 2008). However, the distribution of Cu in particle-size fractions (i.e., sand, silt, clay) can also influence Cu mobilization from the soil during rainfall-runoff events (Roussiez et al, 2013;Wang et al, 2014). Cu can accumulate in the coarse particulate SOM (Besnard et al, 2001;Parat et al, 2002) as well as in finer soil particles that are preferentially mobilized by runoff (Di Stefano and Ferro, 2002).…”