A Kick in the Headwaters: Evaluating a Macroinvertebrate Sampling Method for Ecological Condition Monitoring in Small Streams

Small streams dominate river networks and collectively support high biodiversity, but are rarely included in regulatory biomonitoring programmes. Macroinvertebrate communities are effective biomonitors of ecological condition and are routinely collected using 3-min ‘kick’ samples. However, this 3-min duration may not be suitable for small streams, which typically support fewer taxa at lower densities than larger rivers of equivalent condition. We evaluated the kick-sampling method at 30 sites representing a national small stream monitoring network. At each site, we collected three 5-min kick samples in 10 0.5-min component parts. We used the families collected in 15 min to represent ‘total’ site-scale taxonomic richness, then determined the duration needed to sample ≥ 65% of these taxa (a method and target comparable to those used in larger rivers). We also determined the sampling duration at which an average score per taxon (ASPT) biomonitoring index stabilized. Considering all streams, on average, 2.5-min durations captured ≥ 65% of taxa, but 3.5 min was required to reach this target in temporary streams, because numerous taxa occurred at low abundance. Only 54% of samples contained ≥ 65% of taxa after 2.5 min, compared to 70% after 3 min. In most streams, the ASPT stabilized after 2 min, whereas 3 min was required to meet this target in temporary streams. Considering the variation around any estimate of capture rates introduced by natural variability, taxonomic resolution and operator error, we suggest 3 min as the most robust sampling duration to enable condition monitoring in individual small streams and comparison with larger rivers.