Chafik Maazouzi

Potential impact of invasive amphipods on leaf litter recycling in aquatic ecosystems

The impact of biological invasions on local biodiversity is well established, but their impact on ecosystem functioning has only been sketchily documented. However, biological invasions may impede services provided by aquatic ecosystems, such as, for example, the decomposition of organic matter, a key process in most small streams. To address this question, we experimentally quantified the leaf litter breakdown activity of native and invasive amphipod species, which are keystone species in aquatic ecosystems. The breakdown rate of each species was used to estimate the potential leaf litter recycling in the Rhône and Meurthe Rivers in sites occupied solely by native species and sites dominated by invasive species. We found that invaders were not able to compensate for the activity of native species and that the replacement of native species led to a decrease of at least 66% in the rate of leaf litter recycling. Our approach provides empirical evidence of the functional impact of non-indigenous species on leaf litter recycling, using standard protocols and literature data.

Leaf litter recycling in benthic and hyporheic layers in agricultural streams with different types of land use.

Changes in land use and intensification of agricultural pressure have greatly accelerated the alteration of the landscape in most developed countries. These changes may greatly disturb the adjacent ecosystems, particularly streams, where the effects of pollution are amplified. In this study, we used the leaf litter breakdown rate to assess the functional integrity of stream ecosystems and river sediments along a gradient of either traditional extensive farming or a gradient of vineyard area. In the benthic layer, the total litter breakdown process integrates the temporal variability of the anthropogenic disturbances and is strongly influenced by land use changes in the catchment even though a low concentration of toxics was measured during the study period. This study also confirmed the essential role played by amphipods in the litter breakdown process. In contrast, microbial processes may have integrated the variations in available nutrients and dissolved oxygen concentrations, but failed to respond to the disturbances induced by vineyard production (the increase in pesticides and metal concentrations) during the study period. The response of microbes may not be sensitive enough for assessing the global effect of seasonal agricultural practices. Finally, the leaf litter breakdown measured in the hyporheic zone seemed mainly driven by microbial activities and was hence more affected by vertical exchanges with surface water than by land use practices. However, the breakdown rate of leaf litter in the hyporheic zone may constitute a relevant way to evaluate the impact on river functioning of any human activities that induce massive soil erosion and sediment clogging.

Effect of habitat-related resources on fatty acid composition and body weight of the invasive Dikerogammarus villosus in an artificial reservoir.

Successful invasions are attributed to a combination of adaptations to biotic and abiotic conditions and many studies have highlighted the role of biological traits of invaders in their success. Among the most useful traits for successful establishment in a new ecosystem are the size of the invader and its diet and feeding habits. During the last twenty years, Dikerogammarus villosus has been one of the most successful invaders of large European rivers and lakes. However, regarding feeding habits, results were confusing and sometimes contradictory. In this study, we attempt to define the feeding strategy of D. villosus using their FA content according to sex and the seasonal and the spatial variation in its feeding habit. Our results indicated that D. villosus is rather unspecialized with plasticity in its feeding behaviour, switching between different functional feeding groups depending on seasons, habitats and available resources. The selection of high quality resources may hence provide a strong advantage during the invasion process by optimizing the growth and the reproduction of the invader.

Chronic copper exposure and fatty acid composition of the amphipod Dikerogammarus villosus: results from a field study.

Field study allows assessment of long-term effects on fatty acid (FA) composition of organisms under chronic exposure to metals. One expected effect of copper is peroxidation of lipids and essentially polyunsaturated fatty acids (PUFA). FA analysis was established for the amphipod Dikerogammarus villosus subjected to different degrees of copper exposure (4-40 microg Cu L(-1)). A previous study in our team showed that this species regulates its body Cu concentration (106-135 mg Cu kg(-1) dry weight). Despite the high capacity of bioaccumulation, the absence of a correlation between copper concentration in D. villosus and water prevents its use as bioindicator of copper pollution. Both sexes from the most polluted site showed the lowest total FA content, but the highest PUFA percent, mainly of the long-chained variety (C20-C22). Mechanisms leading to the prevention of lipid peroxidation in this species were discussed (metallothioneins and intracellular granules) and proposed with support from literature data.

Preventive antioxidant responses to extreme oxygen level fluctuation in a subterranean crustacean.

The principal aim of this work was to explore the responses of the groundwater crustacean Niphargus rhenorhodanensis to oxidative stress caused by short- and long-term drastic variations in oxygen level. To this end, we investigated thiobarbituric acid reactive substances (TBARS) levels and anti-oxidative enzyme (SOD and GPx) activities during 24 h anoxia and post-anoxia recovery, and during 10 days of severe hypoxia and post-hypoxia recovery. We observed a decrease in TBARS amounts during recovery from severe hypoxia. Parallel to these results, we observed an overactivation of SOD activity after a 24 h anoxic stress. GPx activity measured at the end of anoxia or severe hypoxia and in the early hours of post-stress recovery also showed an overactivation compared to the control group. We can hypothesize that this overproduction of GPx corresponded to an anticipatory mechanism coping with the overproduction of reactive oxygen species (ROS) during the recovery phase in subterranean animals. This response could be considered as a major asset for life in alternately normoxic and hypoxic conditions, and therefore in extreme biotopes such as groundwaters.

The combined effects of water level reduction and an increase in ammonia concentration on organic matter processing by key freshwater shredders in alluvial wetlands

In a global change context, the intensity and the frequency of drastic low flow periods or drought events will most likely increase to a substantial extent over the coming decades, leading to a modification in the abiotic characteristics of wetlands. This change in environmental parameters may induce severe shifts in plant and animal communities and the functioning of ecosystems. In this study, we experimentally estimated the effect of drought and the accumulation of ammonia (NH3 ) on the feeding activities of three generalist macroinvertebrates (i.e. Gammarus pulex, Gammarus roeselii and Asellus aquaticus) on three types of organic matter: leaves of Berula erecta growing in submerged conditions, leaves of the same species growing in emerged conditions and dead leaves of Alnus glutinosa. We observed a modification in the biomechanical and stoichiometric characteristics of the plants as a result of the emersion of the aquatic plants. This shift produced a substantial decrease in organic matter recycling by invertebrates and in their associated physiological ability (i.e. the energy stores of the animals) to face conditions associated with environmental change. Moreover, the accumulation of NH3 amplified the negative effect of emersion. This snowball effect on invertebrates may profoundly modify the functioning of ecosystems, particularly in terms of organic matter production/degradation and carbon mineralization.

Parasite-induced changes in the diet of a freshwater amphipod: field and laboratory evidence

Trophically transmitted parasites are likely to strongly influence food web-structure. The extent to which they change the trophic ecology of their host remains nevertheless poorly investigated and field evidence is lacking. This is particularly true for acanthocephalan parasites whose invertebrate hosts can prey on other invertebrates and contribute to leaf-litter breakdown. We used a multiple approach combining feeding experiments, neutral lipids and stable isotopes to investigate the trophic ecology of the freshwater amphipod Gammarus roeseli parasitized by the bird acanthocephalan Polymorphus minutus. Infected compared to uninfected amphipods consumed as many dead isopods, but fewer live isopods and less leaf material. Infection had no influence on the total concentration of neutral lipids. Contrary to what we expected based on laboratory findings, the nitrogen isotope signature, which allows for the estimation of consumers trophic position, was not influenced by infection status. Conversely, the carbon isotope signature, which is used to identify food sources, changed with infection and suggested that the diet of infected G. roeseli includes less perilithon (i.e. fixed algae on rocks, stones) but more terrestrial inputs (e.g. leaf material) than that of uninfected conspecifics. This study shows evidence of changes in the trophic ecology of P. minutus-infected G. roeseli and we stress the need to complement feeding experiments with field data when investigating top-down effects of infection in an opportunistic feeder which adapts its diet to the available food sources.

Nutrient and metal pollution of the eastern Gulf of Finland coastline: Sediments, macroalgae, microbiota.

The anthropogenic pollution along the coastline of the eastern Gulf of Finland was studied through a range of methods, including analyses of metal contamination in water, surface sediments, accumulated algal biomass and its correlation with resistant microbiota. According to concentrations, the main pollutants in water were copper and manganese. Influence of Nuclear Power Plant was remarkable in adjacent areas and was expressed in high concentrations of molybdenum, nickel, copper and other elements in the water. Relatively high concentrations of copper, lead and zinc were found in sediments. Microbial tolerance appeared to be correlated with the concentration of the metals in sediments. Higher tolerance levels were found in sediment samples from more polluted stations. Macroalgae, which were massively developed in the coastal zone, had shown high level of metal bioaccumulation. Analyses of carbon, nitrogen and phosphorus content of algal tissues allowed the estimation of additional nutrient loading from accumulated decaying algal biomass on the coastal zone of the eastern Gulf of Finland. Mass development of algae in coastal area may contribute to accumulation of organic matter and associated metals. In our study the highest metal concentrations in sediments were found at the sites with dense and continuous layer of fresh and decaying macroalgal biomass, accompanied by hypoxic conditions. Also our study has shown that accumulated biomass may be a significant source of nutrients in the coastal ecosystem.

Dynamics of dissolved organic carbon (DOC) through stormwater basins designed for groundwater recharge in urban area: Assessment of retention efficiency

Managed aquifer recharge (MAR) has been developed in many countries to limit the risk of urban flooding and compensate for reduced groundwater recharge in urban areas. The environmental performances of MAR systems like infiltration basins depend on the efficiency of soil and vadose zone to retain stormwater-derived contaminants. However, these performances need to be finely evaluated for stormwater-derived dissolved organic matter (DOM) that can affect groundwater quality. Therefore, this study examined the performance of MAR systems to process DOM during its transfer from infiltration basins to an urban aquifer. DOM characteristics (fluorescent spectroscopic properties, biodegradable and refractory fractions of dissolved organic carbon -DOC-, consumption by micro-organisms during incubation in slow filtration sediment columns) were measured in stormwater during its transfer through three infiltration basins during a stormwater event. DOC concentrations sharply decreased from surface to the aquifer for the three MAR sites. This pattern was largely due to the retention of biodegradable DOC which was more than 75% for the three MAR sites, whereas the retention of refractory DOC was more variable and globally less important (from 18% to 61% depending on MAR site). Slow filtration column experiments also showed that DOC retention during stormwater infiltration through soil and vadose zone was mainly due to aerobic microbial consumption of the biodegradable fraction of DOC. In parallel, measurements of DOM characteristics from groundwaters influenced or not by MAR demonstrated that stormwater infiltration increased DOC quantity without affecting its quality (% of biodegradable DOC and relative aromatic carbon content -estimated by SUVA254-). The present study demonstrated that processes occurring in soil and vadose zone of MAR sites were enough efficient to limit DOC fluxes to the aquifer. Nevertheless, the enrichments of DOC concentrations measured in groundwater below infiltration basins need to be considered in future studies to especially assess their impact on groundwater quality.

Ecology-based evaluation of groundwater ecosystems under intensive agriculture: A combination of community analysis and sentinel exposure

Ecological criteria are needed for a comprehensive evaluation of groundwater ecosystem health by including biological components with the physical and chemical properties that are already required by European directives. Two methodological approaches to assess the ecological status of groundwater ecosystems were combined in two alluvial plains (the Ariège and Hers Rivers, southwestern France) varying in agriculture intensity (from grassland to crop rotation including maize and sunflower, and to maize monoculture). In the first approach, the composition of invertebrate assemblages (only obligate-groundwater crustaceans, i.e. stygobionts) sampled in 28 wells differing in their land use contexts was analysed. Abundance, species richness, and assemblage composition significantly changed with agricultural land use or urbanization around the wells. In the second approach, we tested an in situ exposure of sentinel organisms to quantify their response to the environmental pressures. The epigean and native amphipod species Gammarus cf. orinos was used as the sentinel species. Amphipods (30 individuals in each of 10 wells) were exposed for one week to the in situ conditions at two seasons with contrasted concentrations of pollutants. The Ecophysiological Index (EPI) synthetizing the survival rates and energetic storage decreased in wells with low oxygen and high nitrate concentrations, but only during the highest contamination period. Atrazine-related compounds negatively impacted sentinel health whatever the season. The combination of these two approaches may have major applications for orientating groundwater ecosystem management.