Effect of Riparian Vegetation on Channel Complexity and Nutrient Processing in a Subtropical Catchment in Queensland, Australia (11573)
In much of Australia, including Southeast Queensland (SEQ), there are two main drivers for river restoration: the protection and improvement of drinking water quality, and general aquatic ecosystem health (Leigh et al. 2013). Improving riparian vegetation condition via rehabilitation projects aims to mitigate these problems through, for instance, shading stream channels, increasing soil strength, reducing erosion rates, slowing down surface flows and dissipating stream energy. However, there is a lack of data to confirm the reduction in stream bank erosion as a consequence of riparian zone revegetation, which may be due to the time required to measure change. Rutherfurd et al. (2004) concluded that some inherently variable parameters would need to be monitored for significant periods of time (e.g. 80 years for turbidity; 65 yrs for phosphorus) to confidently measure a change in condition.
Monitoring the effect of riparian revegetation projects is complex and time consuming and many studies have used the space for time substitution approach with paired catchments that have similar characteristics (Hardie et al., 2011). In this study, paired sites were selected in the Lake Baroon catchment, southeast Queensland in order to explore the role of riparian zones in trapping sediment and nutrients from the catchment and within channel sources. Paired reaches within the catchment were selected on bed slope, stream order, geology, landuse and extent of vegetation. Channel geometry and riparian vegetation characteristics were compared between degraded and natural reaches along with nutrient concentrations from soil samples taken from the riparian area. Subsamples of each of the composite soils were dried at 40˚C (48 h) and then at 105ºC (16 h) to determine air-dry moisture content (ADMC). Subsamples of both field moist and air-dry composite soils were archived for any future determinations. The bulk of the dried (40°C) samples were sieved (<2 mm and <500 µm), and sent for nutrient analysis using standard methods. Rewetting of soil samples was also undertaken to determine nutrient species leaching from the soils under wetted conditions. Initial results show an effect of riparian vegetation on nutrient processing within the riparian zone and an influence on channel form and stability. The results from the pilot study in the Lake Baroon catchment will be presented.
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