Predictive value of laboratory tests with aquatic invertebrates: influence of experimental conditions

Considering the difficulty of making meaningful extrapolations of laboratory bioassay data to real world situations, short-term tests have been carried out in a factorial pattern to determine the magnitude of effect variation resulting from changes in experimental abiotic conditions.Three selected zooplankton species (the rotifer Brachionus plicatilis, the brine shrimp Artemia salina and the waterflea Daphnia magna) have been exposed to increasing concentrations of two chemicals (one inorganic and one organic) in different combinations of two major environmental variables.For the brackish water rotifer B. plicatilis the acute toxicity of potassium dichromate and sodium laurysulphate was determined in 16 different combinations of temperature and salinity (10-17-24-31°C and 5-20-35-50 pro mille). For the marine crustacean A. salina, the acute toxicity of the same two chemicals was determined in 20 temperature-salinity combinations (10-15-20-25-30°C and 5-20-35-50 pro mille) and for the freshwater crustacean D. magna, 16 combinations of temperature and water hardness (7-14-21-28°C and 80-320-560-800 mg/l CaCO3) were assayed.The entire study comprised nearly 300 complete toxicity tests. 24-h LC50 values (for Artemia and Brachionus) and 24-h EC50 values (for Daphnia) revealed that the variation in toxicity resulting from changing environmental conditions, is both species- and chemical-specific and (within the limits of this study) ranged from a minimum of a factor 2.5 to a maximum exceeding a factor of 100. The necessity to take variations into consideration in predictive hazard assessment studies is underlined

Tree species traits cause divergence in soil acidification during four decades of postagricultural forest development

A change in land use from agriculture to forest generally increases soil acidity. However, it remains unclear to what extent plant traits can enhance or mitigate soil acidification caused by atmospheric deposition. Soil acidification is detrimental for the survival of many species. An in-depth understanding of tree species-specific effects on soil acidification is therefore crucial, particularly in view of the predicted global increases in acidifying nitrogen (N) deposition. Here, we report soil acidification rates in a chronosequence of broadleaved deciduous forests planted on former arable land in Belgium. This region receives one of the highest loads of potentially acidifying atmospheric deposition in Europe, which allowed us to study a ‘worst case scenario’. We show that less than four decades of forest development caused significant soil acidification. Atmospheric deposition undoubtedly and unequivocally drives postagricultural forests towards more acidic conditions, but the rate of soil acidification is also determined by the tree species-specific leaf litter quality and litter decomposition rates. We propose that the intrinsic differences in leaf litter quality among tree species create fundamentally different nutrient cycles within the ecosystem, both directly through the chemical composition of the litter and indirectly through its effects on the size and composition of earthworm communities. Poor leaf litter quality contributes to the absence of a burrowing earthworm community, which retards leaf litter decomposition and, consequently, results in forest-floor build-up and soil acidification. Also nutrient uptake and N2 fixation are causing soil acidification, but were found to be less important. Our results highlight the fact that tree species-specific traits significantly influence the magnitude of human pollution-induced soil acidification

The ‘Coral Bulker’ Fuel Oil Spill on the North Coast of Portugal: Spatial and Temporal Biomarker Responses in Mytilus galloprovincialis

In December 2000, the ship ‘Coral Bulker’ ran aground at the entrance of the port of Viana do Castelo (North–west coast of Portugal). A large amount of fuel oil was spilled and part of it reached the shore. To evaluate the spatial and temporal impact of this oil spill, a field study, and several laboratory toxicity tests were performed using Mytilus galloprovincialis as biological indicator of environmental contamination and the biomarkers glutathione S-transferases (GSTs) and acetylcholinesterase (AChE) as indicative criteria. Fifteen days after the oil spill, mussels collected at stations located near the ship presented higher and lower values of GSTs and AChE activity, respectively. These results, and those obtained in the laboratory toxicity tests, evidence that these biomarkers were sensitive indicators of exposure to this kind of pollution and were able to monitor a spatial impact of the oil spill of at least 10 km, confirming the higher level of contamination near the ship and a contamination gradient along the sampling stations. One year after the accident, such a contamination gradient was no longer evident. This study highlight the potential suitability of a biomarker approach for assessing spatial and temporal impacts of marine pollution accidents, such as fuel oil spills, suggesting the inclusion of these biomarkers in risk assessment studies, as cost-effective and early warning recognized tools. Major advantages and limitations of the biomarker approach used in this study are further discussed