Michel Lafont

Ecosystem engineering at the sediment-water interface: bioturbation and consumer-substrate interaction.

In soft-bottom sediments, consumers may influence ecosystem function more via engineering that alters abiotic resources than through trophic influences. Understanding the influence of bioturbation on physical, chemical, and biological processes of the water–sediment interface requires investigating top-down (consumer) and bottom-up (resource) forces. The objective of the present study was to determine how consumer bioturbation mode and sediment properties interact to dictate the hydrologic function of experimental filtration systems clogged by the deposition of fine sediments. Three fine-grained sediments characterized by different organic matter (OM) and pollutant content were used to assess the influence of resource type: sediment of urban origin highly loaded with OM and pollutants, river sediments rich in OM, and river sediments poor in OM content. The effects of consumer bioturbation (chironomid larvae vs. tubificid worms) on sediment reworking, changes in hydraulic head and hydraulic conductivity, and water fluxes through the water–sediment interface were measured. Invertebrate influences in reducing the clogging process depended not only on the mode of bioturbation (construction of biogenic structures, burrowing and feeding activities, etc.) but also on the interaction between the bioturbation process and the sediments of the clogging layer. We present a conceptual model that highlights the importance of sediment influences on bioturbation and argues for the integration of bottom-up influence on consumer engineering activities.

Biomotoring groundwater contamination: Application to a karst area in Southern France

In order to assess the descriptive value of subterranean organisms with regard to groundwater contamination, faunal sampling was carried out at two unimpacted sites and one sewage-polluted site located in the south-eastern part of the Lez karst system (Hérault, France) from 1991–1993. Invertebrates were collected by means of an air-lift pump in 8 deep monitoring wells (from 43 to 90 m deep) which intersected Cretaceous and/or Jurassic limestones. Wells of the unimpacted sites had faunal assemblages dominated by crustaceans (from 92.4 to 98.3% of the total number of organisms), and they harboured a high number of stygobite species (from 15 to 24) which usually represented a major component of the total number of invertebrates (from 48.1 to 81.5%). At the sewage-polluted site, the wells had significant relative abundances of oligochaetes (from 8.4 to 40.4% of the total number of invertebrates), low stygobite richnesses (from 3 to 7 species) and their groundwater fauna consisted mainly of stygoxene taxa (from 20 to 34) whose relative abundance could be as high as 88%. The spatio-temporal distribution of organisms was related to the groundwater and sewage flow patterns. During low-water periods sewagepolluted water moved preferentially through the conductive fractures of the saturated zone whose faunal assemblages were dominated by stygoxenes such as the polysaprobiont oligochaeteTubifex tubifex. When floods occurred, these stygoxenes were flushed out of the site and were also disseminated throughout the thinly fissured part of the saturated zone where they were associated with stygophiles. As the source of sewage pollution decreased in intensity with time, preliminary signs of groundwater fauna recovery were observed. Oligochaetes became less abundant but recolonization of groundwater by stygobites was not yet observed. On the basis of our results and those of other authors we emphasize the advantages which could result from the development of biomonitoring programmes for the assessment of karstic groundwater contamination.

Use of oligochaete communities for assessment of ecotoxicological risk in fine sediment of rivers and canals of the Artois-Picardie water basin (France)

This study had a purpose to validate different tools based on the oligochaetes for the evaluation of the biological quality of sediments within a surveillance network. Biological data (IOBS index, percentage of Tubificidae with and without hair setae, worm densities), physical data (granulometrics) and chemical data (Cd, Cu, Cr, Hg, Ni, Pb, Zn, PCBs, PAHs) have been studied with co-inertia analysis. These analyses show an opposition between IOBS index and metals, a correlation between metals and percentage of Tubificidae without hair setae, and an association between PAHs, low index values, high densities and high percentage of Tubificidae with hair setae. For 24 sites, biological and chemical data gave similar information. In 11 cases on 36 they are conflicting. The use of metal speciations, according to the method of Teissier et al. (1979), show that the organic matter content seems to have an important role by sorbing metals leading to lower availability. Macrophyte cover could also explain some conflicting results. Granulometrics does not play a determinating role in the present case. As a conclusion, a table allowing the classification of river sediments is proposed for monitoring assessment. This table takes into account IOBS index values, the worm densities and the percentage of Tubificidae without hair setae.

Oligochaete Assemblages in the Hyporheic Zone and Coarse Surface Sediments: Their Importance for Understanding of Ecological Functioning of Watercourses

The hyporheic zone and its interactions with coarse surface sediments is increasingly reported by aquatic ecologists because the water exchanges between surface and subsurface are important factors for the understanding of the ecosystem functioning. However, the hyproheic oligochaete assemblages have received less attention than other assemblages such as crustaceans. In addition, studies investigating the incidence of pollution in watercourses have mostly focused on the benthic zone and have neglected the hyporheic zone. Some examples are given from an unpolluted glacial river (Roseg), polluted plains rivers (Moselle, Rhône) and a protected wetland in an urbanized environment. The hyporheic zone kept the memory of past and present incidences of pollution, in particular when downwellings of polluted surface waters to the hyporheic zone predominated. The Active hydrologic Exchange Describers between surface and subsurface (AED oligochaete species) were the same in the glacial river Roseg, the rivers Rhône and Moselle and the urbanized wetland. The predominance of pollution-tolerant species like Limnodrilus hoffmeisteri was observed in polluted groundwater as well as in polluted surface coarse sediments. Moreover, the urbanized wetland exhibited a high species richness, suggesting that the hyporheic zone is a reservoir of species. The oligochaete communities enable biologists to simultaneously assess the pollution incidence, the permeability of coarse habitats, the water exchanges between surface and subsurface, and give an approximate measure of the metabolic activities in the sediments. Consequently, the simultaneous study of surface and hyporheic oligochaete assemblages is of great interest when considering the ecological functioning of watercourses and the incidence of pollution inputs.

A Comparison of Longitudinal Patterns in Hyporheic and Benthic Oligochaete Assemblages in a Glacial River

This paper examines the longitudinal pattern of oligochaetes in the hyporheic and benthic layers of a glacial river (Val Roseg, Switzerland). We hypothesized that the spatial distribution of oligochaete communities would reflect changes in surface water/groundwater interactions along the river continuum. From June to November 1997 (4 dates), three hyporheic and three benthic samples were collected at 11 and 9 sites, respectively, located over a distance of 11 km from the glacier terminus. A two-ended member mixing model based on concentrations of sodium was used to determine changes in the relative proportions of glacial water and groundwater along the river. The longitudinal increase in the diversity and abundance of hyporheic assemblages of oligochaetes was closely linked to the convergence of groundwater and surface glacial water. The differential distribution of hyporheic and benthic assemblages suggested that the hyporheic corridor acted as the main upstream migration pathway for oligochaetes. In this glacial river, the hyporheic zone appeared as a source area from which benthic habitats presenting suitable environmental conditions could be colonized.

Oligochaete communities as biological descriptors of pollution in the fine sediments of rivers

This study emphasizes the usefulness of Oligochaeta communities as descriptors of pollution in the fine sediments of large rivers. Two indices of biological quality of fine bottoms are proposed and are related to chemical parameters of the water. Tentative proposals are made for an empirical classification of polluted fine sediments.

Surface and Hyporheic Oligochaete Assemblages in a French Suburban Stream

The Chaudanne stream received urban inputs discharged through combined sewer overflows (CSOs). The water quality was not severely impaired, with pollution mainly of organic origin. Oligochaete assemblages were studied in the coarse surface sediments and the hyporheic zone and sampled at four sites on seven occasions during 2000 and 2001. The seasonal distribution of oligochaete assemblages was analyzed by a PCA, the oligochaete species being assigned to functional traits (FTrs). Site 1, located upstream of the CSOs, was characterized by FTrs 1 and 2 (species indicating permeability and those intolerant to water pollution). Below the CSOs, high densities of oligochaetes occurred in the benthic layer of sites 3 and 4, with a predominance of FTr3 (species with tolerance to water pollution). At site 4, FTr4 species (indicative of sludge conditions) constantly predominated in the hyporheic system, but predominated in the benthos only during low stream discharges associated with peaks in CSOs. FTr3 was related to amounts of the oxidized forms of nitrogen, high stream discharges and probably to groundwater upwellings and the sludge tolerant species group (FTr4) was associated with high NH 4 + contents. We are now testing the relevance and generalization of this new approach.

Using aquatic macroinvertebrate species traits to build test batteries for sediment toxicity assessment: Accounting for the diversity of potential biological responses to toxicants

An original species-selection method for the building of test batteries is presented. This method is based on the statistical analysis of the biological and ecological trait patterns of species. It has been applied to build a macroinvertebrate test battery for the assessment of sediment toxicity, which efficiently describes the diversity of benthic macroinvertebrate biological responses to toxicants in a large European lowland river. First, 109 potential representatives of benthic communities of European lowland rivers were selected from a list of 479 taxa, considering 11 biological traits accounting for the main routes of exposure to a sediment-bound toxicant and eight ecological traits providing an adequate description of habitat characteristics used by the taxa. Second, their biological and ecological trait patterns were compared using coinertia analysis. This comparison allowed the clustering of taxa into groups of organisms that exhibited similar life-history characteristics, physiological and behavioral features, and similar habitat use. Groups exhibited various sizes (7-35 taxa), taxonomic compositions, and biological and ecological features. Main differences among group characteristics concerned morphology, substrate preferendum and habitat utilization, nutritional features, maximal size, and life-history strategy. Third, the best representatives of the mean biological and ecological characteristics of each group were included in the test battery. The final selection was composed of Chironomus riparius (Insecta: Diptera), Branchiura sowerbyi (Oligochaeta: Tubificidae), Lumbriculus variegatus (Oligochaeta: Lumbriculidae), Valvata piscinalis (Gastropoda: Valvatidae), and Sericostoma personatum (Trichoptera: Sericostomatidae). This approach permitted the biological and ecological variety of the battery to be maximized. Because biological and ecological traits of taxa determine species sensitivity, such maximization should permit the battery to better account for the sensitivity range within a community.

Superficial and hyporheic oligochaete communities as indicators of pollution and water exchange in the River Moselle, France

Benthic oligochaetes were sampled on three occasions (June, August and October 1992) in the upper (0–10 cm) and hyporheic (35–45 cm depths) sediments at five sites of the River Moselle, from upstream of the town of Epinal to Velle-sur-Moselle. The first site (upstream from Epinal) is considered as unpolluted and the four remaining sites are polluted by industrial effluents. The most polluted stations were generally dominated by the pollution tolerant taxon Limnodrilus. Numbers of individuals of this taxon decreased at the less polluted last site in recovery zone, and were also scarce in the first unpolluted site. It is noteworthy that these tendencies were observed in both superficial and hyporheic substrates and to the greatest degree in hyporheic ones. At the unpolluted site, the hyporheic habitat is dominated by the groundwater species Propappus volki, Pristina spp., Pristinella spp. At the less polluted site (last site), the deep sediments are dominated by groundwater species and the Tubificidae without hair setae decrease from June to October. As a result of water exchange between superficial and subterranean waters, superficial substrates of the first and the last stations tend to be colonised by a high proportion of hyporheic species that suggests that flow is primarily from subterranean to superficial waters. The contrary is the case at other polluted stations which are characterised by the invasion of hyporheic substrates by the pollution tolerant superficial taxa Limnodrilus. This suggests that water flows from the river to the deeper groundwater. These two stations are located near drinking water plants which utilise groundwater, thus increasing the vulnerability of groundwater to surface contaminants.

Molecular barcoding of aquatic oligochaetes: implications for biomonitoring.

Aquatic oligochaetes are well recognized bioindicators of quality of sediments and water in watercourses and lakes. However, the difficult taxonomic determination based on morphological features compromises their more common use in eco-diagnostic analyses. To overcome this limitation, we investigated molecular barcodes as identification tool for broad range of taxa of aquatic oligochaetes. We report 185 COI and 52 ITS2 rDNA sequences for specimens collected in Switzerland and belonging to the families Naididae, Lumbriculidae, Enchytraeidae and Lumbricidae. Phylogenetic analyses allowed distinguishing 41 lineages separated by more than 10 % divergence in COI sequences. The lineage distinction was confirmed by Automatic Barcode Gap Discovery (ABGD) method and by ITS2 data. Our results showed that morphological identification underestimates the oligochaete diversity. Only 26 of the lineages could be assigned to morphospecies, of which seven were sequenced for the first time. Several cryptic species were detected within common morphospecies. Many juvenile specimens that could not be assigned morphologically have found their home after genetic analysis. Our study showed that COI barcodes performed very well as species identifiers in aquatic oligochaetes. Their easy amplification and good taxonomic resolution might help promoting aquatic oligochaetes as bioindicators for next generation environmental DNA biomonitoring of aquatic ecosystems.