Land use impacts on nutrient export in the Central Volcanic Plateau, North Island

Authors: D. Hamilton
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2004, Issue N.Z.J.For. 49(4) 2005, pp 27-31, Jan 2005
Publisher: New Zealand Institute of Forestry

---

Abstract: Different land uses are increasingly being scrutinised for their impacts on downstream waterbodies, particularly in relation to rates of nutrient export. Phosphorus export varies mostly with sediment erosion but nitrogen export is mostly associated with nitrate leaching to groundwater, which is highly variable under different land uses. Both plantation and native forests leach a fraction of the nitrate of most pastoral lands except perhaps just after harvest, but particularly compared with modern farming regimes of addition of labile nitrogenous fertilisers to increase pasture growth and support higher stock numbers.
Recent use of dating techniques to 'age' stream inflows to Lake Taupo and the Rotorua lakes suggest that the effects on stream nitrate concentrations of past conversions of forest to pastoral land and more recent intensification of pastoral land are only partially expressed, as stream inflows are mostly several decades old. Use of riparian buffers, nitrification inhibitors and in-stream and in-lake flocculants may partially offset intensification of land use, but forward thinking is required to mitigate for effects of lag times and achieve a holistic balance of economic, environmental and social aspirations.

---