Metal redistribution by surface casting of four earthworm species in sandy and loamy clay soils.

Bioturbation of metal contaminated soils contributes considerably to redistribution and surfacing of contaminated soil from deeper layers. To experimentally measure the contribution of Allolobophora chlorotica, Aporrectodea caliginosa, Lumbricus rubellus and L. terrestris to soil surface casting, a time-course experiment was performed under laboratory conditions. Earthworms were incubated in perspex columns filled with sandy soil (2% organic matter, 2.9% clay) or loamy clay soil (15% organic matter, 20% clay), and surface casts were collected after up to 80 days. On the sandy soil, A. caliginosa and L. rubellus brought approximately 7.1-16 g dry wt. casts/g fresh wt. earthworm to the surface, which is significantly more than A. chlorotica and L. terrestris (2.5-5.0 g dry wt./g fresh wt.). A. caliginosa was the only species that produced significantly more surface casts in the sandy soil than in the loamy clay soil. In the loamy clay soil, no differences in biomass-corrected casting rates were found among the species. Surface casting rates tended to decrease after 20 days. Considering the densities of the different species in a Dutch floodplain area Afferdensche and Deestsche Waarden, surface cast production is estimated to amount to 2.0 kg dry soil/m2 after 80 days, which could be extrapolated to 2.7-9.1 kg/m2 per year. These amounts correspond to a surface deposition of a layer of approximately 1.9-6.5 mm/year, which is of the same order or even slightly higher than the sedimentation rate and much higher than the amount of soil brought to the soil surface by bioturbating small mammals.

Toxicological risks for small mammals in a diffusely and moderately polluted floodplain.

The ecotoxicological risk of heavy metal pollution in diffusely polluted floodplains is largely unclear, as field-based data are scarce. This study investigated cadmium (Cd) and lead (Pb) accumulation in the liver and kidneys of small mammal species (voles, mice and shrews) from a moderately polluted Dutch floodplain. The Cd and Pb concentrations were compared with effect concentrations (ECs). Reported ECs in literature varied considerably, with the lowest values frequently exceeded by our values, whereas the highest values were encountered only occasionally. Cd and Pb levels were highest in the shrew species, particularly in Sorex araneus. Although toxicological effects at the specimen level were present in these floodplains, effects at population level are thought to be limited, as a result of the animals' relatively short life expectancies (due to recurrent floods) and the rapid maturation of small mammals. Exceptionally high tissue metal concentrations in some specimens of all species indicated local hotspots with peaks in metal concentrations. Sanitizing such local hotspots might reduce toxicological risks.

Ecological effects of diffuse mixed pollution are site-specific and require higher-tier risk assessment to improve site management decisions: a discussion paper.

Many Dutch ecosystems, whether terrestrial, aquatic or sediment-based, are diffusely polluted by mixtures of contaminants, whose concentrations often exceed regulatory Safe Values or other generic quality criteria. This situation has unclear consequences, especially when local authorities are confronted with such pollution. Water managers are frequently in doubt whether their water systems satisfy the criteria for 'Good Ecological Status' as defined in the EU's Water Framework Directive. In case of soils, soil users may wonder whether the soil is 'fit for use'. In case of nature conservation, the problem is that protected species might suffer from toxic stress. Official regulations in these cases call for appropriate action, but it is unclear whether the diffuse exposure causes adverse effects, and what the action should be. This paper proposes and discusses a site-oriented approach in the risk assessment of diffusely contaminated sites that can be used in addition to the compound-oriented policies from which the abovementioned generic quality criteria were derived. The site-oriented approach can be of help in reducing site-specific risks of diffuse contamination. Reflecting on the results of a large Dutch research effort in systems-oriented ecotoxicological effects, the conclusion is drawn that exposure and effects of diffuse pollution are site-specific in kind and magnitude, determined by the local combination of source-pathway-receptor issues, and often not clearly detectable (though often present). To assist in risk management, higher-tier methods can address various aspects, like addressing local mixture composition, bioavailability, and sensitivity of local species groups. Higher-tier risk assessment methods have as yet been developed mainly for cases of serious contamination, like for pesticide management and Risk-Based Land Management. For diffuse pollution, site-specific information can also be used to obtain site-specific exposure and impact information, while practical and ecology-based approaches can be introduced to obtain an integrated overview of the meaning of site contamination and to derive options for managing and reducing the local risks. These issues are discussed against the background of current major policy shifts, in The Netherlands and elsewhere, from a pollutant-oriented assessment to an additional ecological and site-oriented assessment. The latter is most clearly represented in the Good Ecological Status aim of the EU-Water Framework Directive. The paper assesses, integrates and discusses the results of the Dutch research effort in this policy context.

System-oriented ecotoxicological research: which way to go?

This paper presents an overview of the possibilities for further development of tools and. approaches for the ecological assessment and management of diffusively contaminated ecosystems. It is based on the results of the "Netherlands Stimulation Programme on Ecosystem-oriented Ecotoxicological Research", the SSEO programme, which ran from 1998 to 2006, and on opinions of international experts on ecological and ecotoxicological risk-assessment methods and their legal applications. The paper also discusses the pros and cons of the set-up of the SSEO programme. Proper management of diffusively polluted areas has to be based on an integral risk-based and system approach. The approach has to be founded on the relationships between pollution, natural stresses, management measures and the presence and activities of specific species. Furthermore, the relationships between biodiversity in ecosystems and its stability and functioning have to be known. The assessment of aquatic ecosystem quality is now based on the comparisons of the composition of actual species with that of reference species. This type of system does not yet exist for the assessment of soil quality, but it is being developed. It is shown that ecological quality criteria based on a Species Sensitivity Distributions approach are sufficiently conservative to avoid or prevent major ecological impacts of diffuse pollution at concentrations below legal standards. However, a proper quality relationship of biodiversity and ecosystem functioning is lacking in the ecological assessment methods. Future research should focus on the relationship of ecosystem structure (species composition) and ecosystem functioning and on the impact of disturbing the environment and appropriate management measures.

Upgrading system-oriented ecotoxicological research.

In the 1990s the Dutch government expressed the need to investigate the impacts of diffuse pollution at (sub)-ecosystem levels. The resulting Netherlands Stimulation Programme on System-oriented Ecotoxicological Research (SSEO programme) ran from 1998 to 2006. Its primary objective was to assess the impacts of low- to medium-level, diffuse, multiple contaminations on ecosystems. The research results were intended as underpinning for policies on environmental, conservation and nature issues. Research was carried out at three sites that were selected because of their importance for nature management and the presence of diffuse contamination. These sites were: a river meadow/floodplain area (Afferdensche en Deestsche Waarden), an estuarine reed-land area (Biesbosch) and an area of lowland peat soils that had been contaminated with urban waste in past centuries (De Ronde Venen). This introductory paper describes the set-up of the programme, the types of diffuse contamination, the interactions between pollutants and other stress factors, the various methodologies used to integrate the effects on (sub)ecosystem level, and the consequences for formulating policies for and the management of these types of locations. The results of the programme are diverse and complicated and show how difficult it is to draw firm, unambiguous, generic conclusions about the effects at the 'total' ecosystem level. It is however, possible to draw conclusions about effects on major components of ecosystems: 1) The distribution of contaminants, both from a spatial, chemical and ecotoxicological point of view, plays a decisive role in actual effect levels. Even when total contaminant loads are high, such as in estuarine and floodplain areas, bioavailability may be so low that the actual effects are limited. The irregular, heterogeneous, spatial distribution of contaminants in the soil further complicates effect studies, impact assessments and monitoring. 2) Various stress factors, other than contaminants, both natural and anthropogenic, also play a role. The negative effect of the repeated inundation of floodplain areas, for instance, greatly interferes with the impact of contaminants in the lower soil layers. 3) A major problem is to find a method to extrapolate the observations from individual and population levels to the ecosystem level. In addition to traditional food-chain models and similar approaches, the potential of other, not yet extensively explored, ecosystem interaction mechanisms is discussed. 4) Finally, the results have to be interpreted from a policy point of view, both for national soil policies and for implementing the EU Soil Strategy regulations.

The effect of turbation on zinc relocation in a vertical floodplain soil profile.

Turbation is hypothesized to affect the redistribution of heavy metals in polluted floodplain soils by effects on mobility. This hypothesis was tested in microcosms by turbation of zinc-spiked sediment top layers. Manual turbation caused a fast decrease of the zinc content in the upper 15 cm of the soil, even though turbation was only applied to the upper two centimetres. It was especially zinc attached to colloid and organic matter particles that was redistributed from the top layer. Percolation processes resulted in the attached zinc being drained to depths of more than 15 cm. The decrease in zinc content of the topsoil was even stronger in combination with inundation. No indications were found for the redistribution of zinc as a result of an increase of the extractability with 0.01 M CaCl2 or changes in pH. The findings suggest that mechanical turbation and bioturbation may redistribute heavy metals from topsoils in polluted floodplains just after inundation as observed in these turbation experiments.

Automated and continuous redox potential measurements in soil.

Redox potential (Eh) describes the electrical state of a matrix. In soils, Eh is an important parameter controlling the persistence of many organic and inorganic compounds. A popular, but also criticized, manual measuring method makes use of a small tip of Pt placed on a copper wire that is placed in the soil; a reference electrode is placed in the same soil at a fixed distance. Fluctuations in redox potential values measured in the soil can be very large and depth-dependent. This will be overlooked when making single-point measurements. We developed the datalogger Hypnos 2.0 for continuous redox potential and temperature measurements at various depths in the soil and without disturbance of the site. Hypnos is field-deployable, relatively cheap, and runs on batteries. The datalogger can use a "sleep mode" between sampling events. In sleep mode, there is no constant voltage on the Pt wire or the reference electrode, but there is only a short pulse during sampling. We did not measure an effect of this short pulse on the measured redox potential. In sandy soils in mesocosms and in a salt marsh soil we measured changes in the Eh as large as from -400 to +100 mV within 4 d, and daily cycles of 200 mV. Both absolute redox potential values and their diurnal variations were depth-dependent. Because single redox measurements are insufficient in describing redox conditions in some soil systems, Hypnos can be a powerful tool when studying the effects of fluctuating redox conditions on metal availability and pollutant degradation.