Integrated catchment management effects on flow, habitat, instream vegetation and macroinvertebrates in Waikato, New Zealand, hill‐country streams

Abstract

We investigated the short‐term effects on stream now, habitat, water temperature, periphyton biomass, and macroinvertebrate communities of applying integrated catchment management (ICM) to improve the poor economic and environmental performance of a hill farm used for sheep and cattle grazing. Stream responses to a range of changes in land use and riparian management were compared at four reaches in sub‐catchments within a pastoral hill farm area and nearby pasture and native forest reference reaches over 6 years before and 6 years after ICM implementation. At the whole catchment scale, annual runoff from the pasture treatment catchment before ICM was 7% higher than from the native forest reference catchment, and 7‐day low‐flow was 11% lower, but runoff and low now both declined by c. 6%/yr following afforestation (mainly Pinus radiata ) of 62% of the pasture catchment. At sub‐catchment level, pine afforestation with 10 m wide riparian setbacks (site A) was associated with declining channel width, water width, water temperature and periphyton biomass, and increasing periphyton organic content and changes in macroinvertebrate community indices and composition indicating recovery towards reference native forest stream conditions. Site M, involving a mix of partial pine afforestation (36% of catchment) and riparian cattle exclusion with riparian Populus deltoides planting, was associated with generally similar trends to site A. Riparian reforestation with natives and exclusion of all livestock was associated with more rapid reduction in water temperature and streambed cover by fines and macrophytes in a reach with a1m channel (site RS) than a 2 m wide channel (site RM). Reaches with active riparian tree planting had increased streambed cover by small wood and roots. In general, the macroinvertebrates indicated a “rubber band” response to ICM actions, with relatively rapid recovery towards native forest stream macroinvertebrate metric values and faunal composition, although restoration of composition was incomplete. Water temperature reduction was identified as a key factor in this improvement along with the 1–2 km proximity of colonists in undisturbed native forest streams.

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