All Content © CRC for Forestry 2007

Uptake - Issue 1 - Plantation management in riparian zones

This research aims to determine the effects of plantation establishment in a stream-side buffer on various water quality attributes so that regulators and NRM managers can be better informed about the environmental costs and benefits of this practice. The research is being conducted by CSIRO for the CRC for Forestry and the Landscape Logic CERF hub. Planning commenced in 2005, and water quality monitoring commenced in 2007.

Willow Bend Farm

Fig. 1: The paired catchments at Willow Bend Farm. The treated catchment is shown to the left with the 2008-planted buffer. Acacia melanoxylon (blackwood) was planted in the saturated riparian zone, Eucalyptus globulus was planted in the upper third of the buffer, and remainder is planted with E. nitens. The control catchment is immediately to the right of the treated catchment. Below these two catchments, and in the gully to the left of the treated catchment, buffers planted in 2007 are also shown.

 

transect of buffer

Fig. 2. This photo shows a transect across the buffer with spot cultivation by a scoop-and-mound method that increased surface roughness and retained about 50% of grass coverage. Note that the saturated riparian zone (indicated by tussocks) was planted to blackwoods, but not cultivated. Seedlings were planted on the mounds and protected from wildlife browsing by white tree-guards. The buffers will be fenced to exclude stock.

In August this year a stream-side buffer plantation of eucalypts and acacias was established in about 6% of the treated catchment (buffered) of the Willow Bend Farm paired-catchment study. So far, we have not detected any deterioration of water quality. For example, despite steep slopes, soil disturbance due to cultivation, and cultivation as close as 1 m from the saturated riparian zone, a turbidity signal was not detected during concurrent and subsequent storms. In both the treated and untreated catchments, turbidity during baseflow was less than 10 NTUs compared to 20-30 NTUs during storm events. This lack of turbidity during the establishment phase is probably due to the retention of grass, and the creation of surface roughness by the scoop-and-mound spot-cultivation method used. Continued monitoring will indicate if this result is maintained during subsequent storms, and if turbidity increases in the un-buffered catchment relative to the buffered catchment when grazing recommences.

The site of this experiment, which is near Cygnet, Tasmania, has also become the focus of a detailed nitrogen study, which aims to quantitatively model the transport of nitrogen from the grazed hill-slopes, through the stream-side buffer, and into the headwater stream. This research, and its expansion to provide more information on the water budget, involves detailed soil-water monitoring, which has kept our team busy during the past few months (Figs 3 and 4). If this research is successful, the methodology will enable quantitative evaluation of nitrogen buffering effectiveness in a range of contrasting conditions, which would be valuable for guiding NRM investments in this practice. The HYDRUS model is being used to simulate water and solute movement, while detailed nitrogen dynamics is provided by a module designed for constructed wetlands. Our research is the first attempt to apply this modelling combination to a hill-slope situation. Collaboration with the Austrian architect of this module, Dr Guenter Langergraber, has already produced a prototype simulation of nitrogen buffering. Current modelling is using HYRDUS to generate concentration-discharge patterns over timescales ranging from a few minutes to several months (Fig. 5).

dale worledge

Fig. 3. Dale Worledge installing a piezometer

 


TDR water monitoring equipment

Fig. 4. From left, Nico Marcar, Craig Baillie, Vijay Koul and Tivi Theiveyanathan installing TDR water monitoring equipment (or are they watching TV?).





hydrus simulated nitrate dilution

Fig. 5. Example of HYDRUS-simulated nitrate dilution in stream water during a storm. This pattern is similar to published patterns. 

For more information contact Phil Smethurst.