Report: TR 2006/38
Author: Steph Parkyn, Ngaire Phillips, Brian Smith (NIWA)

Abstract

Currently, Environment Waikato (EW) has no basis for evaluating the significance of non-perennial habitats or zero-order stream channels in terms of their indigenous biodiversity. EW have asked NIWA to investigate whether these small streams have biological values that add additional biodiversity to perennial native forest streams and to describe the character of these relatively unstudied stream types that dry up for part of the year. This initial focus was on native forest streams to document baseline values of non-perennial habitats in the absence of human perturbation.

We used channel form (morphological) and surface water (hydrological) characteristics to define the extent and describe the type of non-perennial streams in the Waikato region. The difference between the summer dry season and winter wet season was a general increase in overall stream length in winter. In summer, the character of these headwater streams often followed a pattern of dry channel, mud, isolated pools interspersed by dry or mud habitat, standing water, then flowing water. In winter, the length of flowing or standing water habitat increased in all sites. The average amount of flowing water habitat upstream from the junction with a perennial stream increased from 30 m per stream in summer to 150 m in winter, equivalent to a 5-fold increase on average in the length of stream habitat.

We sampled aquatic invertebrate communities in mud, isolated pools, and flowing water habitats within the non-perennial stream (if that habitat type was present) and in an adjoining perennial stream (if available within native forest). Aquatic macroinvertebrate taxa found in non-perennial headwater habitats differed from those in nearby perennial streams in forested Waikato stream systems in both summer and winter. The communities were particularly different at the top of catchments where streams became isolated pools or mud. Surprisingly, taxa richness was fairly high in the mud samples (on average 15 in summer and 25 in winter) and communities were characterised by the snail Potamopyrgus antipodarum, the tipulid Zelandotipula, and the cased caddisfly Oeconesus maori. In summer, the amount of flowing stream habitat in non-perennial headwaters was reduced and this appeared to be a significant stress resulting in a different configuration of taxa in summer than winter. Total taxa richness was also lower in summer than winter.

Inclusion of non-perennial stream sampling could increase the overall estimate of biodiversity within stream systems as a substantial number of taxa not recorded in the perennial streams occurred in the non-perennial streams (average of 18 and 25 additional taxa in summer and winter, respectively). Therefore, non-perennial streams may harbour elements of indigenous biodiversity not found in perennial habitats and warrant consideration in catchment management and policy development, where biodiversity objectives are of interest.

Aquatic Invertebrate Biodiversity and Spatial Characterisation of Non-Perennial Streams in Native Forest in the Waikato Region [PDF, 393 KB]