16 research outputs found
Influence of macroinvertebrate sample size on bioassessment of streams
In order to standardise biological assessment of surface waters in Europe, a standardised method for sampling, sorting and identification of benthic macroinvertebrates in running waters was developed during the AQEM project. The AQEM method has proved to be relatively time-consuming. Hence, this study explored the consequences of a reduction in sample size on costs and bioassessment results. Macroinvertebrate samples were collected from six different streams: four streams located in the Netherlands and two in Slovakia. In each stream 20 sampling units were collected with a pond net (25×25 cm), over a length of approximately 25 cm per sampling unit, from one or two habitats dominantly present. With the collected data, the effect of increasing sample size on variability and accuracy was examined for six metrics and a multimetric index developed for the assessment of Dutch slow running streams. By collecting samples from separate habitats it was possible to examine whether the coefficient of variation (CV; measure of variability) and the mean relative deviation from the ¿reference¿ sample (MRD; measure of accuracy) for different metrics depended only on sample size, or also on the type of habitat sampled. Time spent on sample processing (sorting and identification) was recorded for samples from the Dutch streams to assess the implications of changes in sample size on the costs of sample processing. Accuracy of metric results increased and variability decreased with increasing sample size. Accuracy and variability varied depending on the habitat and the metric, hence sample size should be based on the specific habitats present in a stream and the metric(s) used for bioassessment. The AQEM sampling method prescribes a multihabitat sample of 5 m. Our results suggest that a sample size of less than 5 m is adequate to attain a CV and MRD of ¿ 10% for the metrics ASPT (Average Score per Taxon), Saprobic Index and type Aka+Lit+Psa (%) (the percentage of individuals with a preference for the akal, littoral and psammal). The metrics number of taxa, number of individuals and EPT-taxa (%) required a multihabitat sample size of more than 5 m to attain a CV and MRD of ¿ 10%. For the metrics number of individuals and number of taxa a multihabitat sample size of 5 m is not even adequate to attain a CV and MRD of ¿ 20%. Accuracy of the multimetric index for Dutch slow running streams can be increased from ¿ 20 to ¿ 10% with an increase in labour time of 2 h. Considering this low increase in costs and the possible implications of incorrect assessment results it is recommended to strive for this ¿ 10% accuracy. To achieve an accuracy of ¿ 10% a multihabitat sample of the four habitats studied in the Netherlands would require a sample size of 2.5 m and a labour time of 26 h (excluding identification of Oligochaeta and Diptera) or 38 h (including identification of Oligochaeta and Diptera). Electronic supplementary material Electronic supplementary material is available for this article at http://dx.doi.org/10.1007/s10750-006-0074-7 and accessible for authorised users
Influence of seasonal variation on bioassessment of streams using macroinvertebrates
The EU Water Framework Directive requires assessment of the ecological quality of running waters using macroinvertebrates. One of the problems of obtaining representative samples of organisms from streams is the choice of sampling date, as the scores obtained from macroinvertebrate indices vary naturally between seasons, confounding the detection of anthropogenic environmental change. We investigated this problem in a 4th order calcareous stream in the western Carpathian Mountains of central Europe, the Stupavsky potok brook. We divided our 100 m study site into two stretches and took two replicate samples every other month alternately from each stretch for a period of 1 year, sampling in the months of February, April, June, August, October and December. Multivariate analysis of the macroinvertebrate communities (PCA) clearly separated the samples into three groups: (1) April samples (2) June and August samples (3) October, December and February samples. Metric scores were classified into two groups those that were stable with respect to sampling month, and those that varied. Of the metrics whose values increase with amount of allochthonous organic material (ALPHA_MESO, hyporhithral, littoral, PASF, GSI new, DSI, CSI), the highest scores occurred in February, April, October and December, while for metrics whose values decrease with content of organic material (DSII, DIS, GFI D05, PORI, RETI, hypocrenal, metarhithral, RP, AKA, LITHAL, SHRED, HAI) the highest values occurred in February, April, June and December. We conclude that sampling twice a year, in early spring and late autumn, is appropriate for this type of metarhithral mountain stream. Sampling in summer is less reliable due to strong seasonal influences on many of the metrics examined while sampling in winter is inappropriate for logistical reasons
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Recent habitat degradation in karstic Lake Uluabat, western Turkey : a coupled limnological-palaeolimnological approach
The Ramsar site of Lake Uluabat, western Turkey, is suffering from eutrophication, industrial pollution and water abstraction, and its naturally-fluctuating water levels are now managed artificially. Here we combine monitoring and palaeolimnological techniques to investigate spatial and temporal limnological variability and ecosystem impact, using an ostracod and mollusc survey to strengthen interpretation of the fossil record. A combination of low invertebrate Biological Monitoring Working Party scores (<10), low ostracod and mollusc diversity across the lake basin, and the dominance of eutrophic diatoms confirms the lake’s poor ecological status. Analysis of organic and carbonate content, diatoms, stable isotopes, ostracods and molluscs in a radiometrically-dated sediment core (ULU20A) indicates a 20th century trend towards increased sediment accumulation rates and eutrophication which was probably initiated by deforestation and agriculture. The most marked ecological shift occurs in ca. 1962, however. A subtle rise in diatom-inferred total phosphorus, coupled with an inferred reduction in submerged aquatic macrophyte cover, accompanies a major increase in sediment accumulation rate; an associated marked shift in ostracod stable isotope data indicative of reduced seasonality and a change in hydrological input indicates impact from artificial water management practises, all of which appears to have culminated in the sustained loss of submerged macrophytes since 2000. We discuss the implications for lake restoration in the context of the EU Water Framework Directive. In a wider context, the results have important implications for the conservation of shallow karstic lakes, the functioning of which is still poorly understood