Variation in root density along stream banks

While it is recognized that vegetation plays a significant role in stream bank stabilization, the effects are not fully quantified. The study goal was to determine the type and density of vegetation that provides the greatest protection against stream bank erosion by determining the density of roots in stream banks. To quantify the density of roots along alluvial stream banks, 25 field sites in the Appalachian Mountains were sampled. The riparian buffers varied from short turfgrass to mature riparian forests, representing a range of vegetation types. Root length density (RLD) with depth and aboveground vegetation density were measured. The sites were divided into forested and herbaceous groups and differences in root density were evaluated. At the herbaceous sites, very fine roots (diameter < 0.5 mm) were most common and more than 75% of all roots were concentrated in the upper 30 cm of the stream bank. Under forested vegetation, fine roots (0.5 mm < diameter < 2.0 mm) were more common throughout the bank profile, with 55% of all roots in the top 30 cm. In the top 30 cm of the bank, herbaceous sites had significantly greater overall RLD than forested sites (alpha = 0.01). While there were no significant differences in total RLD below 30 cm, forested sites had significantly greater concentrations of fine roots, as compared with herbaceous sites (alpha = 0.01). As research has shown that erosion resistance has a direct relationship with fine root density, forested vegetation may provide better protection against stream bank erosion.     

The importance of temperature in assessing iron pipe corrosion in water distribution systems

Temperature is expected to play a significant role in the corrosion of iron pipes in drinking water distribution systems. Temperature impacts many parameters that are critical to pipe corrosion including biological activity, physical properties of the solution, thermodynamic and physical properties of corrosion scale, and chemical rates. Moreover, variations in temperature and temperature gradients may give rise to new corrosion phenomena worthy of consideration by water treatment personnel.     

A test of the senses: fish select novel habitats by responding to multiple cues

Habitat-specific cues play an important role in orientation for animals that move through a mosaic of habitats. Environmental cues can be imprinted upon during early life stages to guide later return to adult habitats, yet many species must orient toward suitable habitats without previous experience of the habitat. It is hypothesized that multiple sensory cues may enable animals to differentiate between habitats in a sequential order relevant to the spatial scales over which the different types of information are conveyed, but previous research, especially for marine organisms, has mainly focused on the use of single cues in isolation. In this study, we investigated novel habitat selection through the use of three different sensory modalities (hearing, vision, and olfaction). Our model species, the French grunt, Haemulon flavolineatum, is a mangrove/seagrass-associated reef fish species that makes several habitat transitions during early life. Using several in situ and ex situ experiments, we tested the response of fish toward auditory, olfactory, and visual cues from four different habitats (seagrass beds, mangroves, rubble, and coral reef). We identified receptivity to multiple sensory cues during the same life phase, and found that different cues induced different reactions toward the same habitat. For example, early-juvenile fish only responded to sound from coral reefs and to chemical cues from mangroves/seagrass beds, while visual cues of conspecifics overruled olfactory cues from mangrove/seagrass water. Mapping these preferences to the ecology of ontogenetic movements, our results suggest sequential cue use would indeed aid successful orientation to novel key habitats in early life.     

Pesticide and agro-ecological transition: assessing the environmental and human impacts of pesticides and limiting their use

Environmental Science and Pollution Research -     

Response of multixenobiotic defence mechanism in Dreissena polymorpha exposed to environmental stress

Multixenobiotic defence mechanism (MXDM) has been recently described as a first line defence system in many aquatic organisms and it has raised attention for its potential as an early biomarker of exposure to environmental stress. In order to investigate the relevance of this biomarker in the freshwater zebra mussel Dreissena polymorpha, we examined its response to exposure and to cessation of exposure. For this purpose, depurated zebra mussels were transplanted to natural rivers or exposed to medium experimentally contaminated with fuel oil 2 in the laboratory. After the exposure period, mussels were submitted to depuration in clean water in the laboratory. The level of MXDM activity was assessed by the efflux method that allows a simple and fast measure of the rate of rhodamine B efflux. MXDM activity was induced following exposure and induction appears earlier after laboratory exposure (3 days) than after in the field exposure (3-14 days). The level of MXDM response could not be directly correlated to exposure dose in the laboratory and to isolated physicochemical parameters or AOX levels in the field. The behaviour of MXDM activity seems to reflect the occurrence of exposure to a global stress rather than to specific compounds. Our results highlighted the possibility to monitor MXDM response in the freshwater zebra mussel. In spite of the difficulty to interpret responses resulting from the lack of specificity of response, multixenobiotic defence mechanism displays qualities to represent a biomarker of general stress in freshwater ecosystems.     

Metal accumulation in intertidal litter through decomposing leaf blades, sheaths and stems of Phragmites australis

Metal contents of decomposing leaf blades, leaf sheaths and stems of common reed (Phragmites australis) were monitored by a litter bag method on the sediment of an intertidal brackish marsh in the Scheldt estuary (The Netherlands). On monthly intervals, two litter bags were retrieved from the marsh during 9 months for both leaf blades and sheaths and during 16 months for stems. All samples were dried, weighed and analysed for ash and Cd, Cu, Cr, Ni, Pb and Zn contents. Most concentrations increased considerably during the decomposition. Generally, also a very important net metal inflow into the litter bags could be observed. The inflow was highest for leaf blades. High correlations between ash contents and metal concentrations for leaf blades suggest that the increase of leaf blade metal contents can be due to physicochemical sorption of dissolved metals and an important infiltration of mud particles, which were not removed by rinsing the leaf blades with distilled water preceding the analyses. For stems, smaller amounts of inflowing ash and even outflowing ash amounts were found, which suggests that inflow of inorganic particles is not the major factor determining metal accumulation by stems on medium term. Ergosterol concentrations in stem tissue however proved to be correlated with metal contents, which suggests a significant role of fungal litter colonizers in metal accumulation. For leaf sheaths, the effects of physicochemical sorption, infiltration of mud particles and incorporation by microbial litter colonizers do not seem to be as pronounced as for stems and leaf blades.     

Uptake and transformation of phenol and chlorophenols by hairy root cultures of Daucus carota, Ipomoea batatas and Solanum aviculare

Hairy root cultures of Daucus carota L., Ipomoea batatas L. and Solanum aviculare Forst were investigated for their susceptibility to the highly toxic pollutants phenol and chlorophenols and for the involvement of inherent peroxidases in the removal of phenols from liquid media. Roots of D. carota grew normally in medium containing 1000 micromol l(-1) of phenol, whilst normal growth of roots of I. batatas and S. aviculare was only possible at levels up to 500 micromol l(-1). In the presence of chlorophenols, normal root growth was possible only in concentrations not exceeding 50 micromol l(-1), except for I. batatas which was severely affected at all concentrations. Despite the reduction in biomass, the growth of S. aviculare cultures was sustained in medium containing up to 2000 micromol l(-1) of phenol or 2-chlorophenol, and up to 500 micromol l(-1) of 2,6-dichlorophenol. The amounts of phenol removed by the roots within 72 h of treatment were 72.7%, 90.7% and 98.6% of the initial concentration for D. carota, I. batatas and S. aviculare, respectively. For the removal of 2,6-dichlorophenol the values were, respectively, 83.0%, 57.7% and 73.1%. Phenols labelled with 14C were absorbed by the root tissues and condensed with highly polar cellular substances as well as being incorporated into the cell walls or membranes. The results suggest that S. aviculare, an ornamental plant, would be best suited for remediation trials under field conditions.     

Converging hazard assessment of gold nanoparticles to aquatic organisms

The gold nanoparticles (Au-NPs) are being increasingly used because of their huge diversity of applications, and consequently, elevated levels in the environment are expected. However, due to their physico-chemical properties and functionalization a high variety of Au-NPs can be found, and complete toxicological information for each type of Au-NPs still lacks, and even, the toxicological information for the same species is sometimes contradictory. Therefore, hazard assessment should be done case by case. Hence, the objective of this study was to obtain ecotoxicological information of the same Au-NPs in aquatic organisms and to find a rationale for Au-NPs toxicity. For such a purpose, bare and hyaluronic acid capped Au-NPs (12.5 nm) along with Au-NPs bulk material were tested on freshwater algae, Daphnia and zebrafish. Results showed that while gold nanoparticles were found to be harmless to the tested organisms, the soluble gold showed to be toxic to algae and Daphnia, with an LC₅₀ between 1 and 2 mg L⁻¹. Comparing our results with those gathered in the literature, it appears that a common hazard assessment of Au-NPs on the studied organisms can be elucidated.