Final LDC WQ Report | Page 56

Table 10 . A , B , C , D Land condition results for Mt Wickham ( pre and post 2018-19 , 2019-20 and 2020-21 wet seasons ).
Land condition (%)
A
B
C
D
Mt Wickham
Treatment : pre-wet ( Nov 2018 )
100
Treatment : post wet ( April 2019 )
78
22
Control : pre-wet ( Nov 2018 )
100
Control : post-wet ( April 2019 )
9
91
Treatment : pre-wet ( Nov 2019 )
6
51
21
23
Treatment : post wet ( April 2020 )
1
42
57
Control : pre-wet ( Nov 2019 )
12
88
Control : post wet ( April 2020 )
4
96
Treatment : post-wet season ( April 2021 )
17
62
20
Control : post-wet season ( April 2021 )
8
92
Water Quality outcomes Installation of the monitoring instrumentation occurred in February 2018 , allowing the collection of baseline ( pre-treatment ) samples prior to works . The results for the 2017-18 ( baseline ), 2018-19 , 2019-20 and 2020- 21 wet seasons are summarised in Table 11 and shown in Figure 15 . Site rainfall varied over the sampling period with the greatest rainfall in 2017-18 (~ 1,100mm ), compared to ~ 650mm in 2020-21 which is close to the long-term average .
In 2018-19 , the unit area sediment yields were much lower at the treatment site (~ 12 t / ha ) compared to the control (~ 52 t / ha ). The low rainfall over the 2019-20 wet season led to only a few small events at both the control and treatment sites , and runoff was generally very low ( Figure 15 ). As a result , the 2019-20 yields were orders of magnitude lower in both the treatment ( 0.09 t / ha / y ) and control ( 0.56 t / ha ) sites . In 2020-21 , the sediment yields were very low at just 0.04 t / ha for the treatment site and 0.43 t / ha for the control site and analysed as being significantly different . When the data were compared across control / treatment both before and after the rehabilitation ( Figure 16 ) the TSS concentrations are still significantly different ( p = 0.012 ). This suggests that the change is greater than would be expected due to changes in climate .
In 2018-19 the unit area total nitrogen ( TN ) loads were lower on the treatment site , but the flow adjusted annual mean concentration of TN and total load was still higher on the treatment site , which is not surprising given that of fertiliser was added to this site to support the establishment of pasture . However , in 2019-20 the total TN loss was considerably lower and comparable between the treatment and control sites ( 1.2 kg / y and 1.7 kg / y respectively ). In 2020-21 , the TN loss was further reduced to 0.5 kg / ha at the treatment site and 0.3 kg / ha at the control site .
56