Isabelle Combroux

Selection of wild macrophytes for use in constructed wetlands for phytoremediation of contaminant mixtures

Constructed wetlands (CWs) offer an alternative to traditional industrial wastewater treatment systems that has been proved to be efficient, cost-effective and environmentally friendly. Most of the time, CWs are planted with proliferative species such as Phragmites australis or with plants originating from nurseries, both representing a risk for the natural biodiversity conservation of aquatic ecosystems located downstream of the CWs. For the removal of metals and organic pollutant mixtures present in industrial effluents, it is necessary to select tolerant plant species that are able to produce a high aboveground biomass and to develop a healthy belowground system. Wild plant species growing in aquatic bodies at industrial outfalls could constitute suitable tolerant species to use in CWs for industrial effluent treatment. To test this hypothesis, we assessed, under laboratory conditions (using an experimental design), the tolerance to mixtures of metals (Al, As, Cd, Cu, Cr, Fe, Mn, Ni, Pb, Sn, Zn) or/and organic pollutants (THC, PHE, PYR, LAS) of five European sub-cosmopolitan native macrophytes (Alisma lanceolatum, Carex cuprina, Epilobium hirsutum, Iris pseudacorus and Juncus inflexus) that had been collected in a polluted Mediterranean wetland, after a field study (crossing ecological relevés and analyses of contaminant concentrations in water and sediments). Our results demonstrated that research on phytoremediation of industrial effluents should focus much more on the use of native macrophytes growing at short distances from industrial discharges (such as C. cuprina in this study), and that root/shoot ratio, aerial height and proportion of green leaves are good and cost-effective indicators of plant tolerance to metals and organic pollutant mixtures in laboratory studies.

Relationships between channelization structures, environmental characteristics, and plant communities in four French streams in the Seine–Normandy catchment

Abstract We examined the relationships between channelization, environmental characteristics, and plant communities in 4 streams (Betz, Cléry, Lunain, and Ecole Rivers) southeast of Paris, France, with the goal of assessing stream health. Seventeen 100-m-long reaches, each divided into a pool/riffle sequence, were monitored in 2006. Each reach had 0 to 3 channelization structures (i.e., embanking, resectioning, and other man-made structures). Redundancy analysis and mean-comparison tests done at 2 spatial scales (reach scale and pool/riffle sequence scale) indicated that channelization significantly affected flow velocity, depth, substrate type, and number of pools/riffles (4 of 24 variables considered). Physical characteristics of the streams were significantly more affected by channelization than were chemical characteristics. Moreover, different channelization structures affected the streams differently. Resectioning and embanking reduced flow velocity and the number of riffles and increased the number of pools. However, man-made structures either accelerated (downstream) or reduced flow velocity (upstream). Channelization strongly affected floristic richness on the basis of biological type (vascular plants, bryophytes, macroalgae) and ecomorphological type (hydrophytes, helophytes) at the pool/riffle sequence scale. Channelization led to taxonomic shifts and loss of biodiversity. Vascular plant taxa such as Helosciadium nodiflorum and Berula erecta were replaced by opportunist taxa such as Potamogeton crispus in channelized reaches. Combinations of channelization structures affected the stream plant assemblages less than did individual structures, a result that suggested compensatory effects. Our study supports the idea that channelization must be accompanied by measures that preserve the initial physical conditions of streams and the natural plant community composition.

Vegetation dynamics in side-channels reconnected to the Rhine River: what are the main factors controlling communities trajectories after restoration?

The hydraulic management of large rivers led to a disconnection of side-channels. Restoration works were to reconnect these side-channels to the main course in order to recover hydrological and ecological functions. The aim of the study was to analyze the vegetation dynamics after restoration and to link it to the change in chemical and hydro-geomorphological characteristics. Changes in species richness, cover and composition of the macrophytes communities were studied in nine side-channels of the Rhine river (France) after reconnection which occurred between 1998 and 2006. Vegetation dynamics was surveyed between 2007 and 2011 and compared to the ones of three target side-channels (never disconnected). Three vegetation communities were identified: one characterized by rheophilic species, a second one by mesotrophic species, and a third one by eutrophic species. Distribution of communities depended mainly on the flow velocity and the sediment texture of the side-channels. The floristic composition of communities evolved rapidly and remained stable a few years after restoration. Changes in species richness and cover remained relatively low in all side-channels over the study period. Time after restoration did not affect the dynamics of colonization. Reconnection allowed the restored side-channels to exhibit vegetation dynamics similar to those of the target side-channels.

Does channelization alter spatial and temporal dynamics of macrophyte communities and their physical habitat

Channelization is the creation of man-made structures that resect, realign, or enclose aquatic systems in order to prevent flooding or to modify their flows for various land uses. The present study examined the impact of this human pressure on the spatial and temporal dynamics of small streams. The physical and floristic characteristics of seventeen reaches in four French rivers were surveyed six times over the course of two years. Macrophyte communities were divided into three biological groups: vascular plants, macroalgae and bryophytes. We used plant functional traits to understand the effects of channelization on community structure. Our results suggest that channelization affected the spatio-temporal dynamic of physical and floristic composition. Channelized reaches were shallower and narrower than non-channelized reaches, i.e. control reaches. They also exhibited different substrate types and dominant species. Differences were mainly observed at the macrohabitat scale, i.e. the pool/riffle scale, within the selected reaches. Alterations in spatio-temporal dynamics of physical and plant composition could be linked to species biological traits. Vascular plants and macroalgae in channelized reaches used a variety of adaptive strategies (e.g. small versus tall size) which allowed them to persist despite environmental differences, whereas plants in control reaches showed a combination of intermediate strategies. Bryophytes were mainly found in control reaches with the exception of Fontinalis antipyretica. These findings could serve as guidelines for future channelization projects and for conservation measures to preserve the dynamics of natural streams.