concentrations measured at the treatment and control sites ( p = 0.363 ) which is interesting given that both sites have very different catchment areas . Despite these catchment differences , the amount of rainfall and runoff at both sites was also very similar . The sediment loads ( t / y ) were much higher at the treatment site , but on a per unit area basis , the control site had higher sediment loads .
( A ) ( B ) Figure 32 . ( A ) TSS concentration and ( B ) TN concentrations at Havilah for the 2020-21 wet season .
The very limited particle size data ( Figure 18 ) collected to date indicates that the sediment in runoff is very fine , around 7 µ M , making it a high priority for management . It is also interesting to note that Havilah has much lower TSS and TN concentrations than the other alluvial gully sites ( Glen Bowen and Mt Wickham ).
4.3.6
Key learnings from gully monitoring
The section below documents some of the additional findings from the study and the implications of these findings for management , policy , further gully rehabilitation and additional areas of research . These conclusions are extracted directly from Bartley et al . ( 2021 ) and included here as they are of direct relevance to this final year of reporting for the LDC Project .
● Across the monitoring sites , annual average soil loss from gullies is strongly dependent on the drainage or catchment area above the gully head-cuts . Catchment area is a surrogate for runoff volume or energy and is the strongest predictor of sediment yield found in this study ; however , other studies have also found soil properties and vegetation condition to be important . Therefore , the land above gullies should continue to be a focus of grazing management or remediation interventions .
● The TSS concentrations varied considerably between control sites with the highest median concentrations measured at Glen Bowen ( 61,000 mg / L ) and Mt Wickham (~ 37,000 mg / L ). Havilah had a median TSS of ~ 18,000 mg / L at the control and 5,800 mg / L at the treatment site . Strathbogie control was 4,500 mg / L and treatment 1,200 mg / L . The lowest median concentrations were at Mt Pleasant control site ( 93 mg / L ).
● The TN concentrations are highly variable between monitoring sites , and between events within sites , and not as responsive as sediment to rehabilitation treatment . This is most likely due to the different drivers of nutrient losses which are not being specifically targeted . Often the introduction of vegetation and organic material used to stabilise the soil and reduce erosion will have the effect of increasing TN and DIN loss from a site . TN concentrations show a similar pattern of variation between sites although the differences are of smaller magnitude than for TSS . The highest TN
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