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This study aims to reveal whether complexity, namely, community and trophic structure, of chronically stressed soil systems is at increased risk or remains stable when confronted with a subsequent disturbance. Therefore, we focused on a grassland with a history of four centuries of patchy contamination. Nematodes were used as model organisms because they are an abundant and trophically diverse group and representative of the soil food web and ecosystem complexity. In a field survey, a relationship between contaminants and community structures was established. Following, two groups of soil mesocosms from the field that differed in contamination level were exposed to different disturbance regimes, namely, to the contaminant zinc and a heat shock. The zinc treatment revealed that community structure is stable, irrespective of soil contamination levels. This implies that centuries of exposure to contamination led to adaptation of the soil nematode community irrespective of the patchy distribution of contaminants. In contrast, the heat shock had adverse effects on species richness in the highly contaminated soils only. The total nematode biomass was lower in the highly contaminated field samples; however, the biomass was not affected by zinc and heat treatments of the mesocosms. This means that density compensation occurred rapidly, i.e., tolerant species quickly replaced sensitive species. Our results support the hypothesis that the history of contamination and the type of disturbance determine the response of communities. Despite that ecosystems may be exposed for centuries to contamination and communities show adaptation, biodiversity in highly contaminated sites is at increased risk when exposed to a different disturbance regime. We discuss how the loss of higher trophic levels from the entire system, such as represented by carnivorous nematodes after the heat shock, accompanied by local biodiversity loss at highly contaminated sites, may result in detrimental effect

Potential of bacterial Communities in biofilms to recover after copper exposure was investigated. Biofilms grown outdoor in shallow water on glass dishes were exposed ill the laboratory to 0.6, 2.1, 6.8 mu mol/l copper amended surface water and a reference and subsequently to un-amended surface water. Transitions of bacterial communities were characterised with denaturing gradient gel electrophoresis (DGGE) and community-level physiological profiles (CLPP). Exposure to 6.8 mu mol/l copper provoked distinct changes in DGGE profiles of bacterial consortia, which did not reverse upon copper depuration. Exposure to 2.1 and 6.8 mu mol/l copper was found to induce marked changes ill CLPP of bacterial communities that proved to be reversible during copper depuration. Furthermore, copper exposure induced the development of copper-tolerance, which was partially lost during depuration. It is concluded that bacterial communities exposed to copper contaminated water for a period of 26 days are capable to restore their metabolic attributes after introduction of unpolluted water in aquaria for 28 days. [KEYWORDS: pollution-induced community tolerance (PICT) ; community-level physiological profiling (CLPP) ; denaturing gradient gel electrophoresis (DGGE) ; bacterial communities ; recovery], Potential of bacterial Communities in biofilms to recover after copper exposure was investigated. Biofilms grown outdoor in shallow water on glass dishes were exposed ill the laboratory to 0.6, 2.1, 6.8 mu mol/l copper amended surface water and a reference and subsequently to un-amended surface water. Transitions of bacterial communities were characterised with denaturing gradient gel electrophoresis (DGGE) and community-level physiological profiles (CLPP). Exposure to 6.8 mu mol/l copper provoked distinct changes in DGGE profiles of bacterial consortia, which did not reverse upon copper depuration. Exposure to 2.1 and 6.8 mu mol/l copper was found to induce marked changes ill CLPP of bacterial communities that proved to be reversible during copper depuration. Furthermore, copper exposure induced the development of copper-tolerance, which was partially lost during depuration. It is concluded that bacterial communities exposed to copper contaminated water for a period of 26 days are capable to restore their metabolic attributes after introduction of unpolluted water in aquaria for 28 days. [KEYWORDS: pollution-induced community tolerance (PICT) ; community-level physiological profiling (CLPP) ; denaturing gradient gel electrophoresis (DGGE) ; bacterial communities ; recovery]

This study reports on the development and application of a whole sediment toxicity test using a benthic cladoceran Chydorus sphaericus, as an alternative for the use of pelagic daphnids. A C. sphaericus laboratory culture was started and its performance under control conditions was optimised. The test was firstly validated by determining dose–response relationships for aqueous cadmium and copper and ammonia, showing a sensitivity of C. sphaericus (96 h LC50 values of 594 µg Cd/L, 191 µg Cu/L and 46 mg ammonia/L at pH 8) similar to that of daphnids. Next, sediment was introduced into the test system and a series of contaminated sediments from polluted locations were tested. A significant negative correlation between survival and toxicant concentrations was observed. It is concluded that the test developed in the present study using the benthic cladoceran C. sphaericus is suitable for routine laboratory sediment toxicity testing. A test was developed for assaying sediment toxicity using a commonly occurring small-bodied cladoceran. [KEYWORDS: Chydorus ; Daphnia ; Laboratory culture ; Sediment toxicity test], This study reports on the development and application of a whole sediment toxicity test using a benthic cladoceran Chydorus sphaericus, as an alternative for the use of pelagic daphnids. A C. sphaericus laboratory culture was started and its performance under control conditions was optimised. The test was firstly validated by determining dose–response relationships for aqueous cadmium and copper and ammonia, showing a sensitivity of C. sphaericus (96 h LC50 values of 594 µg Cd/L, 191 µg Cu/L and 46 mg ammonia/L at pH 8) similar to that of daphnids. Next, sediment was introduced into the test system and a series of contaminated sediments from polluted locations were tested. A significant negative correlation between survival and toxicant concentrations was observed. It is concluded that the test developed in the present study using the benthic cladoceran C. sphaericus is suitable for routine laboratory sediment toxicity testing. A test was developed for assaying sediment toxicity using a commonly occurring small-bodied cladoceran. [KEYWORDS: Chydorus ; Daphnia ; Laboratory culture ; Sediment toxicity test]

The present study aimed to characterise effects of copper and temperature on bacterial communities in photosynthetic biofilms using a suit of supplementary methods: pollution-induced community tolerance (PICT), DNA profiles with denaturing gradient gel electrophoresis (DGGE) and physiological profiles with community-level physiological profiling (CLPP). Biofilms of algae and bacteria were grown in a ditch of a Dutch polder and exposed in the laboratory to copper (3 µM and a reference) at three different temperatures (10, 14 and 20 °C). Bacterial communities sampled from the field showed heterogeneity in their physiological profiles, however the heterogeneity decreased during laboratory incubation. After 3 days laboratory incubation, the copper treated biofilms were different from the reference biofilms, as revealed by DGGE and CLPP analyses. Effects of temperature were not observed in the CLPPs, or in the DGGE profiles. PICT was observed for the bacterial communities at all temperatures. The copper-tolerance at 10 and 14 °C increased about 3 times, whereas copper-tolerance at 20 °C increased about 6 times. Temperature had an effect on the community tolerance, but not on the structure or on the physiological profile, suggesting that temperature was not a major factor causing successional changes under these laboratory conditions. In contrast, temperature had an effect on tolerance development indicating that the exposure to copper was enhanced at higher temperature. [KEYWORDS: Pollution-induced community tolerance (PICT) ; Community-level physiological profiling (CLPP) ; Denaturing gradient gel electrophoresis (DGGE) ; Bacterial communities ; Copper ; Temperature], The present study aimed to characterise effects of copper and temperature on bacterial communities in photosynthetic biofilms using a suit of supplementary methods: pollution-induced community tolerance (PICT), DNA profiles with denaturing gradient gel electrophoresis (DGGE) and physiological profiles with community-level physiological profiling (CLPP). Biofilms of algae and bacteria were grown in a ditch of a Dutch polder and exposed in the laboratory to copper (3 µM and a reference) at three different temperatures (10, 14 and 20 °C). Bacterial communities sampled from the field showed heterogeneity in their physiological profiles, however the heterogeneity decreased during laboratory incubation. After 3 days laboratory incubation, the copper treated biofilms were different from the reference biofilms, as revealed by DGGE and CLPP analyses. Effects of temperature were not observed in the CLPPs, or in the DGGE profiles. PICT was observed for the bacterial communities at all temperatures. The copper-tolerance at 10 and 14 °C increased about 3 times, whereas copper-tolerance at 20 °C increased about 6 times. Temperature had an effect on the community tolerance, but not on the structure or on the physiological profile, suggesting that temperature was not a major factor causing successional changes under these laboratory conditions. In contrast, temperature had an effect on tolerance development indicating that the exposure to copper was enhanced at higher temperature. [KEYWORDS: Pollution-induced community tolerance (PICT) ; Community-level physiological profiling (CLPP) ; Denaturing gradient gel electrophoresis (DGGE) ; Bacterial communities ; Copper ; Temperature]

Item does not contain fulltext, We investigated the effects of copper on the structure and physiology of freshwater biofilm microbial communities. For this purpose, biofilms that were grown during 4 weeks in a shallow, slightly polluted ditch were exposed, in aquaria in our laboratory, to a range of copper concentrations (0, 1, 3, and 10 muM). Denaturing gradient gel electrophoresis (DGGE) revealed changes in the bacterial community in all aquaria. The extent of change was related to the concentration of copper applied, indicating that copper directly or indirectly caused the effects. Concomitantly with these changes in structure, changes in the metabolic potential of the heterotrophic bacterial community were apparent from changes in substrate use profiles as assessed on Biolog plates. The structure of the phototrophic community also changed during the experiment, as observed by microscopic analysis in combination with DGGE analysis of eukaryotic microorganisms and cyanobacteria. However, the extent of community change, as observed by DGGE, was not significantly greater in the copper treatments than in the control. Yet microscopic analysis showed a development toward a greater proportion of cyanobacteria in the treatments with the highest copper concentrations. Furthermore, copper did affect the physiology of the phototrophic community, as evidenced by the fact that a decrease in photosynthetic capacity was detected in the treatment with the highest copper concentration. Therefore, we conclude that copper affected the physiology of the biofilm and had an effect on the structure of the communities composing this biofilm.