Long-term nutrient and vegetation changes in a retired pasture stream: monitoring programme and vegetation survey 1999-2003, updating data from 1976 / Clive Howard-Williams and Stu Pickmere.

October 2005".

Keywords: riparian strips; nitrogen discharge; phosphorus discharge; wetland restoration; stream rehabilitation, plant biodiversity, Lake Taupo, New Zealand.

Includes bibliographical references p. 21.

1. Introduction -- 1.1 Background -- 1.2 Aims -- 2. Methods -- 2.1 Site description -- 2.2 Sampling -- 3. Results -- 3.1 Flow rates -- 3.2 Total suspended solids -- 3.3. Dissolved nutrients -- 3.4 Nutrient removal -- 3.5 Vegetation -- 4. Discussion and conclusions -- 5. Acknowledgements -- 6. References -- Appendix 1 Whangamata Stream nutrient concentration database 1995-2002 -- Appendix 2 Vascular plant species on Whangamata Stream 2003.

This report is part of an on-going long-term study on the Whangamata Stream, north of Lake Taupo, New Zealand, since the stream margins were protected from pastoral farming by the establishment of riparian strips in 1976. The dataset is unique in New Zealand for its continuity and allows a quantitative assessment of the extent and time scales of change in stream restoration programmes. The five years covered here include data from the 2- to 3-monthly samples of flow rate and water quality at two stream sites, a continuation of the photographic record, and a vegetation survey of the stream margins. The biodiversity of the vegetation in the riparian strips continued to increase at a rate of 3% per year. Vascular plants totalled 172 species, of which 70 were indigenous. There was a 2% turnover in species every year and a continuing increase in the proportion of woody species as the vegetation matured. Stream discharge decreased from 0.15 m3/s to 0.03 m3/s, the lowest since 1995. There was a trend for the discharge at the bottom end of the stream to be lower than at the top, which needs further investigation as it implied water loss between the upstream and downstream sampling sites. Both concentration and mass flow of suspended solids declined in the monitoring period, with lowest values recorded in summer at the time of maximum vegetation growth. Marked differences in nutrient concentrations between the top and bottom sampling sites in mid-summer reappeared, and proportionately more nutrient was stripped from the through-flowing water. Intensification of catchment use from pasture to forestry and recent extensive urban development indicate that further changes to this highly valued stream are inevitable.

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