Year

2016

Degree Name

IBSc Hons

ANZSRC / FoR Code

05 ENVIRONMENTAL SCIENCES, 0503 SOIL SCIENCES

Department

School of Earth & Environmental Sciences

Advisor(s)

Tim Cohen

Abstract

Anthropogenic influences and land use practices in eastern Australia over the past 200 years have resulted in vastly altered channel and catchment conditions. This has not only reduced geomorphic diversity but also vegetation diversity and ecological functioning. As such, identifying the impact of various land use regimes is highly important when developing future riparian zone management strategies. To investigate the influence land use (specifically grazing) has on the riparian zone and river system, 12 in-channel river deposits were studied on the Hunter River between Muswellbrook and Aberdeen. Three land use types were selected — i) never grazed, ii) crash grazed and iii) perennially grazed — and samples were taken at three study reaches (Aberdeen, Downstream Aberdeen and Dart Brook Mine). One hundred and eleven (111) soil samples were collected from bars and benches in order to determine organic carbon content and fine sediment retention. The soil samples were analysed using loss-on-ignition (LOI) testing to determine the percentage (%) of organic carbon (OC). The Malvern Mastersizer was used to analyse average grain size and to determine the dominant sediment fraction within each soil sample. Hand sieves (-4 phi and -1 phi) were used to determine the main sediment fractions as a measure of bar variability. Spatial and hydrologic analyses were undertaken to determine historical and recent changes in both vegetation and river geomorphology. Results from the sample analysis showed that sites that had never been grazed had an average increased OC concentration of 6.43% and were also comprised of the finest sediment (FS), at 108.7m. Study locations that had been subjected to controlled grazing (3.02% OC and FS 324.4m) fell on average between permanently grazed (2.68% OC and FS 376.4m) and never-grazed locations across most variables analysed. Riparian zone management is a prevalent and important topic and these results provide guidance for developing management strategies. It has been found that stock may be useful in removing exotic vegetation as part of a larger weed management program, however in doing so they may decrease the amount of carbon sequestered and fine sediment retained. Decreased organic carbon can affect the nutrient cycling and the removal of nitrogen and phosphorus from water prior to entering the stream. In addition, decreased fine sediment retention may result in increased turbidity and therefore decreased light availability throughout the water column. These results may also have implications on global carbon storage through the riparian zone and its associated role in mitigating climate change.

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