Re-engineering buried urban streams: Daylighting results in rapid changes in stream invertebrate communities

Abstract

Stream daylighting is a radical form of restoration which aims to improve morphological, chemical and ecological condition through the re-creation of an open channel from a buried or piped channel. Whilst empirical assessments of its efficacy are lacking, it is hypothesised that the substantial changes in habitat, channel form and energy supply arising from daylighting would lead to a significant changes in stream invertebrate communities, particularly where source populations of macroinvertebrates exist upstream. In this first published study of the ecological outcomes arising from a daylighting project, changes in the invertebrate community were assessed in two reaches of an urban stream catchment in Auckland, New Zealand's largest city, which were daylighted in early 2013. The two reaches allowed a paired assessment, where one of the reaches had a large area of intact native forest in its headwaters. Stream macroinvertebrates were sampled monthly pre- and post-daylighting to assess changes in stream macroinvertebrate communities.Community composition significantly changed pre- to post-daylighting (PERMANOVA Pseudo-F=2.0978, P=0.0018), where communities in different reaches changed by 58% and 71%, respectively. Taxonomic richness did not change with daylighting; however taxa replacements were apparent with 44 new taxa being collected in daylighted reaches and 11 taxa disappearing. Daylighting resulted in marked changes in energy resources and improved habitat in the short-term which altered invertebrate communities from biofilm feeding collector-browser communities to algal grazer communities. Although daylighting did not fully restore these streams from the effects of urbanisation, it is one practical option for the management of urban streams. Further, the presence of a local source population was an important determinant of stream community structure. Where source populations existed upstream community responses to daylighting were greater, including increased abundances of sensitive taxa.