Choice of field and laboratory methods affects the detection of anthropogenic disturbances using stream macroinvertebrate assemblages

Accurate and precise detection of anthropogenic impacts on streams using macroinvertebrates as ecological indicators depends on the use of proper field and laboratory methods. We assessed the responsiveness to anthropogenic disturbances of assemblage metrics and composition by comparing commonly employed alternative combinations of field sampling and taxonomic enumeration methods. Four datasets for our comparisons were derived in the field by 1) conducting multihabitat sampling (MH) or 2) targeted samples in a single habitat (leaf packs – SH) and in the laboratory by 3) counting all individuals of the samples, or 4) simulating subsampling of 300 individuals per sample. We collected our data from 39 headwater stream sites in a relatively small basin of the Brazilian Cerrado. We used a previously published quantitative integrated disturbance index (IDI), based on both local and catchment disturbance measurements, to characterize the intensity of human alterations at each site. Family richness and % Ephemeroptera, Plecoptera and Trichoptera (EPT) individuals obtained from each dataset were tested against the IDI through simple linear regressions, and the assemblage composition between least- and most-disturbed sites was tested using PERMANOVAs. When counting all individuals, differences in taxonomic richness and assemblage composition of macroinvertebrate assemblages between least- and most-disturbed sites were more pronounced in the MH than in the SH sampling method. Leaf packs seemed to concentrate a high abundance and diversity of macroinvertebrates in most-disturbed sites, acting as ‘biodiversity islands’ in these situations, which likely diminished the response of the assemblages to the disturbance gradient when this substrate was targeted. However, MH sampling produced weaker results than SH when subsampling was performed. The % EPT individuals responded better to the disturbance gradient when SH was employed, and its efficiency was not affected by the subsampling procedure. We conclude that no single method was the best in all situations. The efficiency of field and laboratory methods depend on the interactions among each, and the decision of which procedure to use depends on the amount of time and resources available, on the variables of interest, habitat type occurrences, and on the other methods being employed in the sampling protocol.

Impact/Purpose

The effects of methodological decisions on the ability of monitoring and assessment programs to accurately describe biodiversity patterns is a perennial discussion among stream ecologists, and it is one of central importance because the understanding of assemblage patterns and dynamics rely on sampled data. These effects are even more dramatic in the interpretation of ecological indicators of anthropogenic alteration that are obtained from biomonitoring studies and used to guide conservation and management decisions. Ligeiro and colleagues used adaptations of the US EPA’s National Aquatic Resource Survey (NARS) designs and methods to examine the influence of field sampling methods and laboratory counting procedures on the apparent response of stream macroinvertebrate-based bioassessment indicators to anthropogenic disturbance. They collected macroinvertebrate assemblage and physical habitat data from 39 headwater stream sites in a sub-basin within the Cerrado biome of southeastern Brazil. The researchers found that the choice of sampling and processing methods had a significant impact on the ability of an assessment survey to detect of disturbance gradients using macroinvertebrate data in a relatively small geographic area. Moreover, the responsiveness of the bioindicators was affected by the interaction of the field and laboratory sampling methods employed, which makes this matter even more problematic. They concluded that, given sufficient field time and personnel, representative multi-habitat sample and counting all individual organisms collected delivered the best results for almost all the assemblage variables analyzed. On the other hand, the effectiveness of multi-habitat data in discerning the response of macroinvertebrates to a gradient of anthropogenic disturbance gradient was severely diminished when the number of organisms counted was restricted by sub-sampling a fixed number of organisms from the original collection taken from the streams. By contrast, single habitat samples were more resistant to degradation from smaller counts, but they were not as responsive to changes in habitat composition as were the multihabitat sampling procedures. Similar adaptations of NARS designs, field methods, and approaches for assessing ecological condition have been applied in state and basin stream surveys throughout the U.S. and internationally, but have been especially innovative in Brazil. These applications are not only valuable tests of the NARS approaches, but contribute to environmental science, resource management, and conservation of biodiversity through new understandings of natural and anthropogenic controls on biota and physical habitat in streams.

Citation

Ligeiro, R., R. Hughes, Phil Kaufmann, J. Heino, A. Melo, AND M. Callisto. Choice of field and laboratory methods affects the detection of anthropogenic disturbances using stream macroinvertebrate assemblages. Elsevier Science Ltd, New York, NY, 115:106382, (2020). [DOI: 10.1016/j.ecolind.2020.106382]

DOI: Choice of field and laboratory methods affects the detection of anthropogenic disturbances using stream macroinvertebrate assemblages