One of the features of riparian zones
is their ability to significantly reduce nitrogen loads entering streams, by
removing nitrate from groundwater interacting with their sediments. In this
paper, we present a novel GIS technique that helps land managers identify riparian
areas where rehabilitation activities are likely to be most effective in reducing
stream nitrogen loads through increasing denitrification. The methodology
identifies high-priority areas as those that have both a high potential for
riparian denitrification and have nearby land uses that are likely to generate
high nitrogen loads (e.g., due to fertiliser use). For this purpose, we define
the Rehabilitation Index, which is the product of two other indices, namely,
the Nitrate Removal Index and the Contaminant Interception Index. The latter
identifies the nitrate contamination potential for each raster cell in the riparian
zone by examining the quantity and proximity of agricultural land use. The Nitrate
Removal Index is estimated using a conceptual model for surface-water/groundwater
interactions in the carbon-rich root zones of riparian buffers belonging to
middle-order perennial streams; nitrate is removed due to denitrification when
base flow interacts with the carbon-rich riparian sediments before discharging
into a stream. The technique requires a high-resolution digital elevation model,
land use rasters, and soil type rasters. Riparian buffers that are relatively
low in the landscape, have a flat topography, and have medium hydraulic conductivity
soils that allow sufficient residence time and a relatively shallow water table
are most conducive to denitrification. In this paper we describe the technique
and present maps for targeted riparian restoration from a trial implementation
for the Maroochy catchment, South East Queensland, Australia.