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Aylmers Valley Stream

The Banks Peninsula (BPZ) has an area of 8010 km2 and forms the most prominent volcanic feature of the South Island. Geologically the peninsula comprises of the remnants of two large volcanoes which means streams in this area have naturally higher phosphorus concentrations than other waterways in Canterbury. Estimates suggest native forest once covered 98% of the peninsula. However less than 2% remains today. 

Twelve streams around the BPZ area are included in Environment Canterbury’s state of the environment monitoring programme. Main pressures on streams within the BPZ come from agricultural activities (particularly difficulty in fencing out stock) and subsequent increased phosphorus runoff. Because these streams are naturally higher in phosphorus, they are susceptible to excessive nutrient concentrations which may lead to degraded water quality and poorer instream aquatic communities.

Streams within the BPZ, typically have high dissolved phosphorus concentrations, and relatively low dissolved nitrogen concentrations. This is largely due to phosphorus-rich soils and generally low input from groundwater. Bacterial concentrations are often very high due to the steep terrain and difficulty fencing out stock. Good riparian management in this catchment can assist in reducing the likelihood of excessive phosphorus and bacteria entering streams. Lake Forsyth (Wairewa) is a lowland lake in the zone that has significantly degraded water quality and suffers from toxic cyano-bacterial blooms most summers. This is linked to high phosphorus levels, the shallow nature of the lake and the lack of a natural surface water outlet for the lake.

Sites 2

Monitored sites in the Aylmers Valley Stream catchment

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