Development of standard protocols for macroinvertebrate assessment of soft‐bottomed streams in New Zealand

Abstract

Macroinvertebrate communities in hard‐bottomed (HB) and soft‐bottomed (SB) streams were compared to address questions on sample substrata, sample area, and data interpretation. Communities at HB and SB reference sites (native bush catchments) were distinctly different. SB reference sites had 50% of the total taxa, 33% of the Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa, and significantly lower Macroinvertebrate Community Index (MCI) and Semi‐Quantitative MCI (SQMCI) scores than HB reference sites. Ten EPT genera were abundant (>20 individuals per sample) at HB reference sites compared with one EPT genus (Zephlebia) at SB reference sites. The densities of macroinvertebrates at SB reference sites were <10% of those at HB sites indicating the need to sample a larger area to obtain a representative sample. SB sites with severe urban and rural land use disturbance had significantly lower metric values than SB reference sites. The SQMCI was the only metric sensitive to moderate disturbance, and multivariate ordination further supported the value of relative abundance data in detecting moderate impairment in SB streams. Hand sampling of submerged wood added 16–40% more taxa in total, and 11–44% more EPT taxa to sweep‐net samples, indicating the importance of directly sampling wood in SB streams. The results supported separate collection methods and data interpretations for HB and SB streams proposed in recently published New Zealand protocols.