Abstract
The use of aquatic macroinvertebrates as bio-indicators in water quality studies has increased considerably over the last decade in Costa Rica, and standard biomonitoring methods have now been formulated at the national level. Nevertheless, questions remain about the effectiveness of different methods of sampling freshwater benthic assemblages, and how sampling intensity may influence biomonitoring results. In this study, we compared the results of qualitative sampling using commonly applied methods with a more intensive quantitative approach at 12 sites in small, lowland streams on the southern Caribbean slope of Costa Rica. Qualitative samples were collected following the official protocol using a strainer during a set time period and macroinvertebrates were field-picked. Quantitative sampling involved collecting ten replicate Surber samples and picking out macroinvertebrates in the laboratory with a stereomicroscope. The strainer sampling method consistently yielded fewer individuals and families than quantitative samples. As a result, site scores calculated using the Biological Monitoring Working Party-Costa Rica (BMWP-CR) biotic index often differed greatly depending on the sampling method. Site water quality classifications using the BMWP-CR index differed between the two sampling methods for 11 of the 12 sites in 2005, and for 9 of the 12 sites in 2006. Sampling intensity clearly had a strong influence on BMWP-CR index scores, as well as perceived differences between reference and impacted sites. Achieving reliable and consistent biomonitoring results for lowland Costa Rican streams may demand intensive sampling and requires careful consideration of sampling methods.
Highlights
Aquatic biological monitoring has had a major impulse in the past decade, and aquatic macroinvertebrates have become important indicators of environmental quality
In Costa Rica, the Biological Monitoring Working Party- Costa Rica (BMWP-CR) biotic index was adopted in the Executive Decree No 33903-S-Ministry of Environment and Energy (MINAE) (Ministerio de Ambiente y Energía, Propuesta de Ley del Recurso Hídrico, 2007) for the assessment of the environmental quality of waters
The aims of this study were to: 1) compare the sensitivity of BMWPCR biotic index using two sampling methodologies: qualitative sampling with a strainer and replicate Surber samples, 2) determine the main differences between the abundance and taxonomic richness that can be found with each method and their influence in the result of the index, and 3) examine the sensitivity of Biological Monitoring Working Party-Costa Rica (BMWP-CR) biotic index to sampling intensity using the replicate Surber samples
Summary
Aquatic biological monitoring (i.e., biomonitoring) has had a major impulse in the past decade, and aquatic macroinvertebrates have become important indicators of environmental quality. Some studies have shown the importance of continuing to evaluate factors which can influence the outcome of the index, such as sampling time (Maue & Springer, 2008) and the use of different methods for collecting aquatic macroinvertebrates (Stein, Springer & Kohlmann, 2008). We consider it appropriate to continue in this direction, evaluating the different options that can be used in biomonitoring, in order to obtain more accurate and appropriate assessments of the environment quality of water. The Surber is a quantitative method that is less dependent on the operator experience, and offers less flexibility for sampling different stream habitat types
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