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Typha angustifolia, Juncus maritimus, and Eleocharis palustris were evaluated for de-icing salt removal from runoff water. Plants were exposed to a range of de-icing salt levels (0.2, 0.7, 4, 8, and 13 dS m(-1)) in laboratory-scale subsurface constructed wetlands (CWs) for 2 months under greenhouse conditions. Effluent characteristics, plant height, biomass, and Cl and Na removal rates and uptake were monitored. More water volume was retained in CWs of T. angustifolia (∼60 %) than of J. maritimus and E. palustris (∼37.5 %), which accounted for the electrical conductivity increase in effluents (1.3-1.9-fold). Based on the NaCl removal rate, T. angustifolia showed the greatest phytodesalinization ability (31-60 %) with the highest removal at the lowest salt levels (0.2-0.7 dS m(-1)), followed by J. maritimus (22-36 %) without differences in removal among levels, and E. palustris (3-26 %) presenting a removal rate highly decreased with increasing salt levels. Plant height and biomass were stimulated at low de-icing salt levels, but, at higher levels, T. angustifolia and E. palustris growth was inhibited (tolerance index ∼67 and 10 %, respectively, in the worst cases). Salt amounts in aboveground biomass in g m(-2) differed among levels and ranged as follows: 13.6-29.1 (Cl), 4.2-9.3 (Na; T. angustifolia); 7.0-12.0 (Cl), 2.7-6.4 (Na; J. maritimus); and 0.9-7.6 (Cl), 0.3-1.6 (Na; E. palustris). Chloride and Na translocation decreased with de-icing salt increase in T. angustifolia, while no significant differences were found in J. maritimus, which is interesting for harvesting purposes.

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Abstract:Winter road network management is a source of anthropogenic salinity in the Saint-Augustin Lake watershed (Quebec City, QC, Canada). To prevent the potential impact caused by road runoff involving de-icing salts (NaCl) and trace metals (Cd and Pb) on the watershed, a full-scale treatment chain system (including a detention basin, a filtering bed, and a constructed wetland) was built. Average Cl and Na concentrations in groundwater were higher in wells affected by road network (125 mg/L Cl and 64 mg/L Na) than in control wells (13 mg/L Cl and 33 mg/L Na) suggesting a contamination by de-icing salts. The monitoring of influent and effluent surface water in the treatment system has shown a seasonal dependence in NaCl concentrations and electrical conductivity values, being the highest in summer, linked with the lower precipitation and higher temperature. Concentration ranges were as follows: 114-846 mg/L Na and 158-1757 mg/L Cl (summer) > 61-559 mg/L Na and 63-799 mg/L Cl (spring and autumn). The treatment system removal efficiency was significant, however with seasonal variations: 16%-20% Cl, 3%-25% Na, 7%-10% Cd and 7%-36% Pb. The treatment system has shown an interesting potential to mitigate the impact of anthropogenic salinity at watershed scale with higher expected performances in the subsequent years of operation.

Mediterranean climate characteristics and carbonate are key factors governing soil heavy-metal accumulation, and low organic matter (OM) content could limit the ability of microbial populations to cope with resulting stress. We studied the effects of metal contamination on a combination of biological parameters in soils having these characteristics. With this aim, soils were spiked with a mixture of cadmium, copper, lead, and zinc, at the two limit values proposed by current European legislation, and incubated for ≤12 months. Then we measured biochemical (phosphatase, urease, β-galactosidase, arylsulfatase, and dehydrogenase activities) and microbial (fungal and bacterial DNA concentration by quantitative polymerase chain reaction) parameters. All of the enzyme activities were strongly affected by metal contamination and showed the following inhibition sequence: phosphatase (30-64 %) < arylsulfatase (38-97 %) ≤ urease (1-100 %) ≤ β-galactosidase (30-100 %) < dehydrogenase (69-100 %). The high variability among soils was attributed to the different proportion of fine mineral fraction, OM, crystalline iron oxides, and divalent cations in soil solution. The decrease of fungal DNA concentration in metal-spiked soils was negligible, whereas the decrease of bacterial DNA was ~1-54 % at the lowest level and 2-69 % at the highest level of contamination. The lowest bacterial DNA decrease occurred in soils with the highest OM, clay, and carbonate contents. Finally, regarding the strong inhibition of the biological parameters measured and the alteration of the fungal/bacterial DNA ratio, we provide strong evidence that disturbance on the system, even within the limiting values of contamination proposed by the current European Directive, could alter key soil processes. These limiting values should be established according to soil characteristics and/or revised when contamination is produced by a mixture of heavy metals.

The contribution of the nature instead of the total content of soil parameters relevant to metal bioavailability in lettuce was tested using a series of low-polluted Mediterranean agricultural calcareous soils offering natural gradients in the content and composition of carbonate, organic, and oxide fractions. Two datasets were compared by canonical ordination based on redundancy analysis: total concentrations (TC dataset) of main soil parameters (constituents, phases, or elements) involved in metal retention and bioavailability; and chemically defined reactive fractions of these parameters (RF dataset). The metal bioavailability patterns were satisfactorily explained only when the RF dataset was used, and the results showed that the proportion of crystalline Fe oxides, dissolved organic C, diethylene-triamine-pentaacetic acid (DTPA)-extractable Cu and Zn, and a labile organic pool accounted for 76% of the variance. In addition, 2 multipollution scenarios by metal spiking were tested that showed better relationships with the RF dataset than with the TC dataset (up to 17% more) and new reactive fractions involved. For Mediterranean calcareous soils, the use of reactive pools of soil parameters rather than their total contents improved the relationships between soil constituents and metal bioavailability. Such pool determinations should be systematically included in studies dealing with bioavailability or risk assessment.