Do high levels of diffuse and chronic metal pollution in sediments of Rhine and Meuse floodplains affect structure and functioning of terrestrial ecosystems?

This paper (re)considers the question if chronic and diffuse heavy metal pollution (cadmium, copper, lead and zinc) affects the structure and functioning of terrestrial ecosystems of Biesbosch National Park, the floodplain area of rivers Meuse and Rhine. To reach this aim, we integrated the results of three projects on: 1. the origin, transfer and effects of heavy metals in a soil-plant-snail food chain; 2. the impact of bioavailability on effects of heavy metals on the structure and functioning of detritivorous communities; 3. the risk assessment of heavy metals for an herbivorous and a carnivorous small mammal food chain. Metal pollution levels of the Biesbosch floodplain soils are high. The bioavailability of metals in the soils is low, causing low metal levels in plant leaves. Despite this, metal concentrations in soil dwelling detritivores and in land snails at polluted locations are elevated in comparison to animals from 'non-polluted' reference sites. However, no adverse effects on ecosystem structure (species richness, density, biomass) and functioning (litter decomposition, leaf consumption, reproduction) have been found. Sediment metal pollution may pose a risk to the carnivorous small mammal food chain, in which earthworms with elevated metal concentrations are eaten by the common shrew. Additional measurements near an active metal smelter, however, show reduced leaf consumption rates and reduced reproduction by terrestrial snails, reflecting elevated metal bioavailability at this site. Since future management may also comprise reintroduction of tidal action in the Biesbosch area, changes in metal bioavailability, and as a consequence future ecosystem effects, cannot be excluded.

Heavy metal pollution affects consumption and reproduction of the landsnail Cepaea nemoralis fed on naturally polluted Urtica dioica leaves.

This study is one of the very first that investigates the effects of heavy metal pollution on food consumption and reproduction of terrestrial snails under semi-realistic field conditions. Two experiments were carried out using snails (Cepaea nemoralis) and food (Urtica dioica leaves) from different metal polluted locations and one reference location. The first experiment showed that both polluted and reference snails fed on high-metal leaves from a highly polluted location had significantly lower consumption rates than snails consuming leaves from the reference location. In the second experiment, snails from both locations used in the consumption experiment and from two low-polluted locations were kept on native soil and food in order to reproduce. No negative effect of heavy metal pollution on clutch size was found for the snails from the reference location and the low-polluted locations. Snails from the highly polluted location laid no eggs. This suggests that at high levels of metal pollution, reproduction is strongly negatively affected. We suggest that the absence of egg laying by snails from the highly polluted location results from a combination of decreased consumption and an increased demand of energy for the accumulation and detoxification of metals (decreased scope for growth).