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Article Dans Une Revue International Journal of Environmental Analytical Chemistry Année : 2011

Multi-tracer experiments to characterise contaminant mitigation capacities for different types of artificial wetlands

Résumé

Salt tracers (sodium bromide/sodium chloride) and two different fluorescent tracers, uranine (UR) and sulforhodamine-B (SRB), were injected as a pulse into six different surface flow wetlands (SFWs). Salt tracers documented wetland hydraulics. The fluorescent tracers were used as a reference to mimic photolytic decay (UR) and sorption (SRB) of contaminants as illustrated by a comparison to a real herbicide (Isoproturon), which was used as a model for mobile pesticides. Tracer breakthrough curves were used to document residence time distributions, hydraulic efficiencies, peak attenuation and retention capacities of completely different wetland systems. A 530m2 forest buffer zone showed considerable peak attenuation but limited retention capabilities despite its large area. Approximately 80% of SRB was permanently retained in a re-structured 325m2 flood detention pond. These two non-steady SFWs indicated long-term tracer washout. The remaining four SFWs displayed constant outflow rates and steady-state flow conditions. Due to photolytic decay in a 330m2 row of three wetlands, UR was almost entirely degraded, but the SRB breakthrough suggested relatively low sorption. A 65m2 shallow flow-through wetland yielded negligible photolytic decay but showed considerable sorption losses. Finally two types of vegetated ditches were analysed. In one case, vegetation was removed from a 413m long ditch immediately prior to tracer injection. A 30% loss by sorption to sediment and plant remnants occurred at the very beginning of the tracer breakthrough. Inside a second ditch, 80m long and densely vegetated by Phragmites australis, sorption was even higher and yielded eightfold higher specific SRB retention rates. Although the present findings are only valid for low flow conditions, they indicate that a shallow water depth seems to be a key variable which may increase sorption of tracers and therefore contaminants. Large wetlands with deep water bodies may attenuate concentrations efficiently, but unit load reduction was found to be more significant in shallow systems even at much higher flow velocities.
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Dates et versions

hal-02595648 , version 1 (15-05-2020)

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Citer

J. Lange, Tobias Schuetz, C. Gregoire, D. Elsässer, R. W. Schulz, et al.. Multi-tracer experiments to characterise contaminant mitigation capacities for different types of artificial wetlands. International Journal of Environmental Analytical Chemistry, 2011, 91 (7-8), pp.768-785. ⟨10.1080/03067319.2010.525635⟩. ⟨hal-02595648⟩
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