Daniel Cluzeau

The use of invertebrate soil fauna in monitoring pollutant effects

Abstract A critical review of biological parameters used to indicate pollutant impact on soil quality was conducted. These parameters mention some soil invertebrates. The value of an indicative organism depends on its life expectancy, life style and specific importance. Nematodes, mites, collembolans, enchytraeids, earthworms, isopods and molluscs are good potential biological indicators. Biological indicators of bioaccumulation and biological indicators of effects (toxicological and ecological) can be distinguished. Bioaccumulation studies are difficult to interpret, as wide variations could be found, depending on taxonomic group, habitat, organ studied, soil type or even pollutant type. Some groups, such as Collembola, require in depth bioaccumulation studies. It is suggested to use a pool of macro-concentrators, including at least some earthworm, isopod and gastropod species. Toxicological indicators have been well studied and their lethal and sublethal pollutant effects are well known. However, studies have focused on only a few species, such as the earthworm Eisenia foetida or the collembolan Folsomia candida . These studies should be extended to other zoological groups, as well as to several species from the same group, to generate a representative test battery. Exposure biomarkers and physiological change studies should be emphasised, as they act as very early warning systems of contamination. Data are currently lacking on how soil biological processes malfunction due to pollution. We need to explore the links between pollutant effects on soil fauna and pollutant effects on soil functioning. Concerning ecological indicators, studies should develop sampling techniques and parameters, which are specific to ecotoxicological goals. Before-after impact control procedures should be carried out, to eliminate the background noise of the study site and only evaluate the influence of pollutants. On the other hand, ecological indices, such as taxonomic diversity or richness, should be used carefully especially concerning chronic pollution. Effects of pollutants on biological cycle studies seem very promising, but need further information on the life history strategies of many species. Furthermore, the pollutant tolerance of rare species should be considered. The different types of biological indicators yield complementary information on pollutant effects. They all need standard procedures. In this context, studies should be extended and diversified, and associate bioaccumulation, toxicological and ecological indicators to provide better information on soil quality.

X-ray tomographic and hydraulic characterization of burrowing by three earthworm species in repacked soil cores

To test the assumption that different earthworm species make differently-structured burrow systems that can affect water permeability, the burrow systems made by adults of three earthworms species (Lumbricus terrestris, Nicodrilus giardi and Octalasion lacteum) were studied in repacked soil cores (20 cm diameter by 40 cm high) under controlled conditions of temperature and humidity. Five core were used for each species and one adult earthworm was incubated per soil core over 21 days. Three-dimensional reconstruction (skeletons and volumetric images) of the burrow systems was performed and characterized after computer analysis of the 2D-slices from X-rays tomography. Total burrow length, number of burrows, branching rate, connectivity, burrow continuity, mean verticality and mean sinuosity of the burrows were measured from the skeletons. Differences were found between species in burrow characteristics: only one vertical and continuous burrow with large diameter for L. terrestris; long and complex burrow systems with branching burrows for N. giardi and O. lacteum. Moreover, 3D volume reconstruction of burrow systems enabled determination of the total volume, the distributed burrow volume as a function of depth and, using the tools of mathematical morphology, the pore size distribution of burrows. Results showed that the burrow volume of N. giardi was the highest; the three species had a unimodal pore size distribution centered on 8, 7 and 5 mm in diameter for L. terrestris, N. giardi and O. lacteum, respectively. Saturated hydraulic permeability was measured for each core and predicted using a water flow model. Significant differences between species were found, the burrow systems made by N. giardi being the most efficient for water flow. Differences in hydraulic properties between species resulted mainly from the difference in burrow continuity, the presence of openings at the soil surface and the burrow depth penetration.

Changes of pore morphology, infiltration and earthworm community in a loamy soil under different agricultural managements

Abstract Earthworm activity produces changes at different scales of soil porosity, including the mesoporosity (between 1.000 and 30 μm eq. dia.) where both water retention and near-saturated infiltration take place. At this scale, the structural changes are poorly described in temperate agricultural systems, so we do not yet fully understand how these changes occur. The present study was conducted to determine the relationships between the morphology of the mesopores, which is mainly affected by earthworm activity, and the hydrodynamic behaviour (near-saturated infiltration) of topsoil under different agricultural managements inducing a large range of earthworm populations. Investigations were carried out at the soil surface in three fields under different management practices giving rise to three different earthworm populations: a continuous maize field where pig slurry was applied, a rye-grass/maize rotation (3/1 year, respectively) also with pig slurry, and an old pasture sown with white clover and rye-grass. Pore space was quantified using a morphological approach and 2D image analysis. Undisturbed soil samples were impregnated with polyester resin containing fluorescent pigment. The images were taken under UV light, yielding a spatial resolution of 42 μm pixel−1. Pores were classified according to their size (which is a function of their area) and their shape. Hydraulic conductivity K(h) was measured using a disc infiltrometer at four water potentials: −0.05, −0.2, −0.6, and −1.5 kPa. The abundance and ecological categories groups of earthworms were also investigated. Continuous soil tillage causes a decrease in both abundance and functional diversity (cf. maize compared with old pasture) when soil tillage every 4 years causes only a decrease in abundance (cf. rotation compared with old pasture). There were no relationships between total porosity and effective porosity at h=−0.05 kPa. Image analysis was useful in distinguishing the functional difference between the three managements. Fewer roots and anecic earthworms resulted in fewer effective tubular voids under maize. There were fewer packing voids in the old pasture due to cattle trampling. Greater hydraulic conductivity in the pasture phase of rotation may arise from a greater functional diversity than in the maize and absence of cattle trampling compared with the pasture. We point to some significant differences between the three types of agricultural management. A better understanding is required of the influence of agricultural management systems on pore morphology. This study provides a new methodology in which we consider the earthworm activity as well as community in order to assess the effects of agricultural management on soil structure and water movement.

Earthworm activity and soil structure changes due to organic enrichments in vineyard systems

Abstract The effect of organic enrichment on earthworm activity and soil structure was studied in two French vineyards, by comparing control and test plots. In each vineyard the organic matter quantitatively increased the abundance and biomass of the earthworm community. These increases were associated with a higher level of species diversity and a higher evenness corresponding to the development of endogeic community. These earthworm community changes were associated with an increase in granular bioturbated areas and in macroporosity in the top soil layer. The micromorphological approach incorporated an original process of image analysis which appeared to be an appropriate method for characterizing pore morphology in this study. The pores when characterized by their size and shape could be related to ecological groups and growth stages of earthworms.

Influence of temperature and food source on the life cycle of the earthworm Dendrobaena veneta (Oligochaeta)

Abstract The life cycle of Dendrobaena veneta was studied to assess the potential of breeding this species for the fish-bait market. Development, growth and reproduction were investigated by rearing worms at 10°, 15°, 20° or 25°C on horse manure or on aerobic paper sludge for 6 months. At 10°C, the maturity was slow with a long period of development (104 d) and a low cocoon production. Productivity at 25°C was better than at 20°C or 15°C. The effect of temperature on cocoon production differed according to the source of food; on paper sludge, cocoons were produced at the same rate at 20 or 25°C while on horse manure cocoon production was better at 25°C than at 20°C. Whatever temperature, cocoon production was significantly greater on paper sludge than on horse manure. On paper sludge, maturation of juveniles was faster and adult worms larger. Adults started to produce cocoons at a younger age and more cocoons were produced worm −1 and d −1 . These results showed that the life cycle of D. veneta may be influenced by the type of food and that horse manure is not the best substrate for breeding this species.

A new simulation for modelling the topology of earthworm burrow systems and their effects on macropore flow in experimental soils

Abstract. Earthworm burrows (i.e. macropores) are organised in burrow systems with various geometric properties. These burrow systems have a significant effect on soil processes, particularly the movement of water in the soil. But the relationships between earthworm burrow systems and their hydraulic properties are not well established because experimental studies of burrow geometry are difficult to perform. Although X-ray computed tomography has revolutionised the 3D description of burrow systems, this method is both time consuming and expensive. This paper presents a new, cheap and rapid approach. A computer model simulating the burrowing behaviour of earthworms was developed from experimental studies. A saturated flow model was then superimposed on the structure of the simulated burrow system to explore the relationships between the burrow systems and their hydraulic properties. Simulations of individual burrow systems were obtained for two different species of earthworm belonging to different ecological groups. Structural parameters of burrow systems (pore space, interconnectedness, connectivity and the number of openings at the limits of the space) were calculated and linked with estimates of permeability using regressions. In our results connectivity gave the best prediction of the difference in permeability between the two sets of burrow systems determined by the burrowing behaviour of the earthworms. Pore space, interconnectedness and the number of burrow openings explained fewer variations.

Assessment of earthworm contribution to soil hydrology: a laboratory method to measure water diffusion through burrow walls

The capacity for water diffusion in burrow walls (i.e. the coefficient of sorptivity) either burrowed by Lumbricus terrestris (T-Worm) or artificially created (T-Artificial) was studied through an experimental design in a 2D terrarium. In addition, the soil density of earthworm casts, burrow walls (0–3 mm around the burrow) and the surrounding soil (>3 mm) were measured using the method of petroleum immersion. This study demonstrated that the quantity of water which transits through burrows of L. terrestris in the soil matrix was lower than that transited through soil fractures, due to a reduction of soil porosity in burrow walls (compaction: cast > worm’s burrow walls > surrounding soil > artificial burrow walls). Earthworm behaviour, in particular burrow reuse with associated cast pressing on walls, could explain the larger burrow wall compaction in earthworm burrows. If water diffusion was lower through the compacted burrows, burrow reuse by the worms makes them more stable (worms would maintain the structure over years) than unused burrows. The present experimental design could be used to test and measure the specific differences between earthworm species in their contributions to water diffusion. Probably, these contributions depend on the presumed related-species behaviours which would determine the degree of burrow wall compaction.

Earthworm effects on gaseous emissions during vermifiltration of pig fresh slurry.

Treatment of liquid manure can result in the production of ammonia, nitrous oxide and methane. Earthworms mix and transform nitrogen and carbon without consuming additional energy. The objective of this paper is to analyse whether earthworms modify the emissions of NH(3), N(2)O, CH(4) and CO(2) during vermifiltration of pig slurry. The experiment used mesocosms of around 50 L, made from a vermifilter treating the diluted manure of a swine house. Three levels of slurry were added to the mesocosms, with or without earthworms, during one month, in triplicate. Earthworm abundance and gas emissions were measured three and five times, respectively. There was a decrease in emissions of ammonia and nitrous oxide and a sink of methane in treatments with earthworms. We suggest that earthworm abundance can be used as a bioindicator of low energy input, and low greenhouse gas and ammonia output in systems using fresh slurry with water recycling.

Burrowing behaviour of radio-labelled earthworms revealed by analysis of 3D-trajectories in artificial soil cores

Summary A new apparatus called ‘gamma column’ developed by Capowiez et al. (2001), enables the continuous movements of radio-labelled earthworms to be tracked in artificial soil cores (3D-space). The present study aimed at analysing the patterns of creation and use of burrow systems by earthworms. Each individual was radio-labelled by injecting a small source of 60 Co (13μCi) into its coelomic cavity and then incubating them separately in artificial soil cores for 21 days. The continuous movements of earthworms were classified as three kinds of movements (“to dig”; “to move forwards”; “to move backwards”). Break points that defined the limits between these movements were either the inversion of the displacement of the earthworm or the start of a new burrowing phase. Trajectories of the individuals (one of Lumbricus terrestris and one of Nicodrilus giardi ) were analysed and qualitative differences were found: L. terrestris built only one vertical burrow in punctuated bouts of activity and, between these short digging events, oscillated many times up and down in its burrow. N. giardi displayed distinct phases of digging, when it built a more complex burrow system with several branches, and phases of use when it oscillated equally from the top to the bottom of the core. Even though it was based on only one observation per species, this preliminary work provides a promising description of the dynamics of burrowing behaviour and tests their hypothetical species-specificity under artificial conditions.

Evolution of non-dissolved particulate organic matter during composting of sludge with straw.

Long term composting induces loss of C and organic matter stabilisation. These two processes may have opposite effects on long term carbon storage in soils. To check whether raw materials should be composted or not before being spread on the soil, changes in particle size fractions were quantified during composting of 9 tons of sewage sludge and straw. Both the mass of the fine fraction (<2 microm) and the amount of carbon contained in it increased after seven months, respectively, +37% and +43%. The fine fraction contributes to carbon sequestration. A literature review supported the assumption that composting should increase long term C storage. Nevertheless, soil texture or agricultural practices modify the behaviour of this fraction. Thus, the fractionation method used for soils is relevant to predict the effect of composting as a mitigation option in greenhouse gas reduction strategies, but is not sufficient in itself.