Institute News

Conference 2003
Greening the City:
Bringing Biodiversity Back
into the Urban Environment


Aquatic Macrophyte Planting: a Novel Way to Improve the Effectiveness of Stream Enhancement Programmes?

Alastair Suren, Scott Larnard & Marty Flanagan (NIWA, Christchurch)

Among aquatic ecosystems, urban streams have undergone some of the most severe and diverse human-caused modifications, with large changes to hydrological, geomorphological, and chemical conditions, and resultant changes to biological health. Techniques for restoring or rehabilitating urban streams are at an early developmental stage. Four topics in particular have received considerable recent attention: channel rehabilitation, bank stabilization, riparian revegetation, and fish (salmonid) population recovery. Rehabilitation of benthic biota and in-stream processes such as primary production has generally been neglected. People undertaking stream restoration programmes make an implicit assumption that physical rehabilitation will be followed by natural colonization of native species, and recovery of in-stream processes.

Submerged and amphibious macrophytes are important components of many stream ecosystems. Macrophytes generate particulate nutrients, provide habitat for epiphytes, invertebrates and fish, and modify streamflow, sediment structure, and sediment and water chemistry. Re-establishment of stream macrophytes following rehabilitation projects in agricultural areas has been associated with improved water quality and increased biodiversity. These observations suggest that native macrophytes could be an important element of urban stream rehabilitation, and their active introduction may help improve biodiversity of restored stream sections.

In February 2002, the Christchurch City Council commenced a stream enhancement project at Papanui Stream, with the aim to create conditions favouring a stable, self-sustaining ecosystem. A wooden-lined box drain was removed from a 330 m stream reach and a new channel excavated. The streambed was lined with geo-textile and gravel, then cobbles were added to form riffles. Channel construction was completed in August 2002.

Three native macrophyte species (Callitriche petriei, Myriophyllum triphyllum, and Potamogeton cheesmanii) were raised in a nearby rural stream from locally sourced cuttings, and introduced into the lower 200 m section of the enhanced reach of Papanui Stream during October 2002. An upstream 100 m section was left unplanted as a control. Our objectives in this study were to assess the survival and growth of native macrophyte species transplanted into a newly-constructed stream channel and to evaluate the effects of transplanted macrophytes on stream community structure.

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The Community Trust
Landcare Research

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Last updated: October 10, 2003