water quality

Successful possum control operations were conducted in 1990, using aerially-sown sodium monofluoroacetate (1080) possum baits, at Waipoua (85% kill) and on Rangitoto Island (93% kill). In Waipoua Forest Sanctuary, streams and rivers were monitored for 4 months after 100 tonnes of 1080 possum baits were sown over 17 000 ha of forest. At Rangitoto Island, adjacent to Auckland, surface and ground water samples were analysed for 6 months after 20 tonnes of 1080 possum baits were sown over the 2300 ha island.

The impact of discharging an oxidation pond effluent into a wetland in the Waitangi Forest (Northland) was assessed by comparing the water, soil, and vegetation of this wetland (the sewage wetland) with that of an adjacent wetland not receiving effluent (the reference wetland). The hydroperiod of the two wetlands differs markedly with the sewage wetland now permanently flooded whereas the reference wetland is subject to summer drawdown. Marked differences were found in gross chemical indicators such as pH and redox potential between the soils of the 2 wetlands.

The legume gorse (Ulex europaeus) is one of the most widespread nitrogen (N) fixing species and is also one of the most invasive weeds of New Zealand. Despite its widespread occurrence, little research has been undertaken on N cycling in gorse ecosystems. This lack of knowledge is important since gorse covers up to 900 000 ha in New Zealand and there is a potential for a large environmental impact from the cycling of large amounts of N fixed by gorse entering waterways and water bodies.