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Brisbane, Australia

Olley J.,Griffith University | Burton J.,Griffith University | Smolders K.,Seqwater | Pantus F.,Griffith University | Pietsch T.,Griffith University
Hydrological Processes | Year: 2013

Previous studies using fallout radionuclides (137Cs and 210Pbex) to determine the relative contributions of surface-soil and channel erosion (including gullies and channel banks) to stream sediments have used a relatively small number of composite samples (<25) to characterize the source end members, and concentrations in each of the source end members have, through the use of means and standard errors, been assumed to be normally distributed. Here, we examine 137Cs activity concentrations to determine the erosion processes supplying sediment in seven water supply catchments in South-east Queensland. First, we test some of the underlying assumptions in the method using concentrations of 137Cs and 210Pbex in composite samples collected from 109 surface-soil sites and 39 channel-bank sites. Paired composite samples, each consisting of 20 subsamples, from five sites are used to demonstrate that this sampling approach was sufficient to average out any local variations in surface-soil 210Pbex and 137Cs concentrations across the 300m2 sampled. We derive probability distributions for 137Cs and 210Pbex concentrations in the group of samples from each of the end members and show that only the distribution of 210Pbex in samples from surface soils is normally distributed. We use the probability distributions for 137Cs, which provides the greatest discrimination between sources, to show that the 137Cs concentrations on the river sediment samples are consistent with channel erosion being the dominant source. Conservation works aimed at reducing the supply of sediments in these catchments should therefore focus on rehabilitation of the channel network and decreasing the runoff to the channel network. These findings are consistent with other similar studies on tropical Australian rivers. © 2012 John Wiley & Sons, Ltd. Source

Cao H.,University of Adelaide | Recknagel F.,University of Adelaide | Orr P.T.,Seqwater
Ecological Modelling | Year: 2013

This paper presents the functionality of the newly designed hybrid evolutionary algorithm (HEA) applied for synthesizing predictive rules from complex ecological data by providing the options for: (a) modelling single or multiple rules and (b) optimizing model parameters by Hill Climbing (HC) or Differential Evolution (DE). The effectiveness of the improved HEA is tested by predictive modelling of chlorophyll-a and the tropical cyanobacteria Cylindrospermopsis monitored in the Wivenhoe Reservoir in Queensland (Australia) from 1998 to 2009. The paper validates results of the alternative optimization algorithms and model structures, and provides insights into ecological relationships captured by the models by means of sensitivity analyses. © 2012 Elsevier B.V. Source

Kerr J.G.,Griffith University | Burford M.A.,Griffith University | Olley J.M.,Griffith University | Bunn S.E.,Griffith University | Udy J.,Seqwater
Water Research | Year: 2011

This study examined the link between terrestrial and aquatic phosphorus (P) speciation in the soils and sediments of a subtropical catchment. Specifically, the study aimed to identify the relative importance of P speciation in source soils, erosion and transport processes upstream, and aquatic transformation processes as determinants of P speciation in lake sediments (Lake Wivenhoe). Using a sequential extraction technique, NH4Cl extractable P (NH4Cl-P; exchangeable P), bicarbonate-dithionite extractable P (BD-P; reductant soluble P), NaOH extractable P (NaOH-rP; Al/Fe oxide P), HCl extractable P (HCl-P; apatite-P), and residual-P (Res-P; organic and residual inorganic P) fractions were compared in different soil/sediment compartments of the upper Brisbane River (UBR) catchment, Queensland, Australia. Multidimensional scaling identified two distinct groups of samples, one consisting of lake sediments and suspended sediments, and another consisting of riverbed sediments and soils. The riverbed sediments and soils had significantly higher HCl-P and lower NaOH-rP and Res-P relative to the lake and suspended sediments (P < 0.05). Analysis of the enrichment factors (EFs) of soils and riverbed sediments showed that fine grained particles (<63 μm) were enriched in all but the HCl-P fraction. This indicated that as finer particles are eroded from the soil surface and transported downstream there is a preferential export of non-apatite P (NaOH-rP, NaOH-nrP, BD-P and Res-P). Therefore, due to the preferential erosion and transport of fine sediments, the lake sediments contained a higher proportion of more labile forms of inorganic-P relative to the broader soil/sediment system. Our results suggest that a greater focus on the effect of selective erosion and transport on sediment P speciation in lakes and reservoirs is needed to better target management strategies aimed at reducing P availability, particularly in P-limited water bodies impacted by soil erosion. © 2011 Elsevier Ltd. Source

Kerr J.G.,Griffith University | Burford M.,Griffith University | Olley J.,Griffith University | Udy J.,Seqwater
Biogeochemistry | Year: 2011

Phosphorus (P) is often a key limiting nutrient in freshwater systems, and excessive P can result in algal blooms, with flow-on effects to aquatic food webs. P sorption is an important process in aquatic and terrestrial ecosystems whereby phosphate (PO4 3-) is exchanged between liquid and solid phases. This study shows that differences in the concentration of PO4 3- in a subtropical river system during high and low flow can be attributed to differences in P sorption characterises of its catchment soils and sediments. The sediments have lower Equilibrium Phosphate Concentrations (EPC0) and higher binding energy (Kd); the surface soils have higher EPC0 and higher easily desorbed P (NH4Cl-P). A comparison of filterable reactive phosphorus (frP) in water samples collected at high and low flows, with soil and sediment EPC0, suggested that during event flows, the high EPC0 and NH4Cl-P of surface soils is producing a net movement of PO4 3- from the soil/sediment system into runoff and stream flow. At baseflow, there is more likely a net movement of PO4 3- into the riverbed sediments. This has important implications for management actions aimed at reducing P loads to river systems and downstream water storages, namely the need to increase the infiltration of rainfall to decrease the amount of PO4 3- being flushed from the surface soil. © 2010 Springer Science+Business Media B.V. Source

Bertone E.,Griffith University | Stewart R.A.,Griffith University | Zhang H.,Griffith University | O'Halloran K.,Seqwater
Journal of Hydrology | Year: 2015

This paper presents an extensive investigation of the mixing processes occurring in the subtropical monomictic Advancetown Lake, which is the main water body supplying the Gold Coast City in Australia. Meteorological, chemical and physical data were collected from weather stations, laboratory analysis of grab samples and an in-situ Vertical Profiling System (VPS), for the period 2008-2012. This comprehensive, high frequency dataset was utilised to develop a one-dimensional model of the vertical transport and mixing processes occurring along the water column. Multivariate analysis revealed that air temperature and rain forecasts enabled a reliable prediction of the strength of the lake stratification. Vertical diffusion is the main process driving vertical mixing, particularly during winter circulation. However, a high reservoir volume and warm winters can limit the degree of winter mixing, causing only partial circulation to occur, as was the case in 2013. This research study provides a comprehensive approach for understanding and predicting mixing processes for similar lakes, whenever high-frequency data are available from VPS or other autonomous water monitoring systems. © 2015 Elsevier B.V. Source

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