( A ) ( B ) Figure 30 . ( A ) TSS concentration and ( B ) TN concentrations at Strathbogie for four wet seasons .
The limited particle size data ( Figure 18 ) collected to date indicates that the sediment in runoff is very fine , around 6 µ M , making it a high priority for management .
In summary , the results show that there has been a reduction in the concentration of sediment ( TSS ) and nitrogen ( TN ) at the treatment site , compared to the control site , following the second year of treatment . However , this change is not significant when all the data are combined to compare control and treatment sites across years .
The condition of the landscape in terms of cover and biomass has also changed between treatment and control site for most of the vegetation attributes in 2020 / 21 , however , these are not significantly greater than differences between the control and treatment site prior to the remediation . Further years of higher rainfall will help to assess whether these preliminary improvements can be sustained .
As the treatment site had no runoff or samples in the 2019 / 20 wet season , the effectiveness value was ~ 1.0 , as the treatment appeared to ‘ cut off ’ all runoff and water quality for that year . This year the treatment was no longer significant relative to previous years , and we assigned an effectiveness rating of 0 . These two years together give an effectiveness value of ~ 0.5 or 50 %. The dramatic changes in data between years at this site highlight the benefits of long-term temporal monitoring to assess treatment effectiveness .
Treatment
This year represented the first year of baseline data collection at the Havilah site . The treatments are planned for the second half of 2021 . It is unknown whether grazing management will form a part of the treatment at this site , however , pasture surveys have been set up above the gullies anticipating that this will be part of the approach for this site .
There were some challenges in selecting a control and treatment gully at this site , as the gullies that were comparable in terms of gully form and soil type , were either too small to gauge , were all under-going treatment or had significantly different catchment areas . The latter being the case with final sites selected , with the treatment site draining a much larger area ( 1770 ha ) compared to the control gully ( 94 ha ).
Onsite vegetation , runoff and water quality data was collected by CSIRO , commencing in 2021 .
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