Monitoring land use change in the Lake Taupo catchment between 1975, 1990 and 2002 using satellite remote sensing data

Conversion of native vegetation into farmed grassland in the Lake Taupo catchment commenced in the late 1950s. The lake’s iconic value is being threatened by the slow decline in lake water quality that has become apparent since the 1970s. This decline is due to increased nitrogen (N) leaching from the catchment, with 95% of the ‘manageable’ leached N estimated to be sourced from livestock farms. We report the usefulness of land use change data derived from historic satellite scenes (1975, 1990 and 2002), as a means of identifying critical areas within this large catchment that might warrant targeting for management change to help reverse the declining water quality. There were no large amounts of farmland or exotic forestry developed from indigenous vegetation after 1975. However, reducing the area of bare soil in grassland and exotic forest land use classes is suggested as one approach that may help reduce N leaching to ground water and the lake.