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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.

Recknagel F.,University of Adelaide | Orr P.T.,Seqwater | Cao H.,University of Adelaide
Harmful Algae | Year: 2014

Seven-day-ahead forecasting models of Cylindrospermopsis raciborskii in three warm-monomictic and mesotrophic reservoirs in south-east Queensland have been developed by means of water quality data from 1999 to 2010 and the hybrid evolutionary algorithm HEA. Resulting models using all measured variables as inputs as well as models using electronically measurable variables only as inputs forecasted accurately timing of overgrowth of C. raciborskii and matched well high and low magnitudes of observed bloom events with 0.45≤r2>0.61 and 0.4≤r2>0.57, respectively. The models also revealed relationships and thresholds triggering bloom events that provide valuable information on synergism between water quality conditions and population dynamics of C. raciborskii. Best performing models based on using all measured variables as inputs indicated electrical conductivity (EC) within the range of 206-280mSm-1 as threshold above which fast growth and high abundances of C. raciborskii have been observed for the three lakes. Best models based on electronically measurable variables for the Lakes Wivenhoe and Somerset indicated a water temperature (WT) range of 25.5-32.7°C within which fast growth and high abundances of C. raciborskii can be expected. By contrast the model for Lake Samsonvale highlighted a turbidity (TURB) level of 4.8 NTU as indicator for mass developments of C. raciborskii. Experiments with online measured water quality data of the Lake Wivenhoe from 2007 to 2010 resulted in predictive models with 0.61≤r2>0.65 whereby again similar levels of EC and WT have been discovered as thresholds for outgrowth of C. raciborskii. The highest validity of r2=0.75 for an in situ data-based model has been achieved after considering time lags for EC by 7 days and dissolved oxygen by 1 day. These time lags have been discovered by a systematic screening of all possible combinations of time lags between 0 and 10 days for all electronically measurable variables. The so-developed model performs seven-day-ahead forecasts and is currently implemented and tested for early warning of C. raciborskii blooms in the Wivenhoe reservoir. © 2013 Elsevier B.V.

Thompson J.,University of Queensland | Roach A.,Office of Environment and Heritage | Eaglesham G.,39 Health | Bartkow M.E.,SEQWater | And 2 more authors.
Marine Pollution Bulletin | Year: 2011

Perfluorinated alkyl compounds (PFCs) including perfluorooctane sulphonate (PFOS) and perfluorooctanoate (PFOA) were measured in environmental samples collected from around Homebush Bay, an urban/industrial area in the upper reaches of Sydney Harbour and Parramatta River estuary. Water, surface sediment, Sea Mullet (Mugil cephalus), Sydney Rock Oyster (Saccostrea commercialis) and eggs of two bird species; White Ibis (Threskiornis molucca), and Silver Gull (Larus novaehollandiae) were analysed. In most samples PFOS was the dominant PFC. Geometric mean PFOS concentrations were 33. ng/g. ww (wet weight) in gull eggs, 34. ng/g. ww in ibis eggs, and 1.8. ng/g. ww and 66. ng/g. ww in Sea Mullet muscle and liver, respectively. In sediment the PFOS geometric mean was 1.5. ng/g, in water average PFOS and PFOA concentrations ranged from 7.5 to 21. ng/L and 4.2 to 6.4. ng/L, respectively. In oysters perfluorododecanoic acid was most abundant, with a geometric mean of 2.5. ng/g. ww. © 2011 Elsevier Ltd.

Sinha R.,University of New South Wales | Pearson L.A.,University of New South Wales | Davis T.W.,Griffith University | Burford M.A.,Griffith University | And 2 more authors.
Water Research | Year: 2012

The bloom-forming, toxic cyanobacterium, Cylindrospermopsis raciborskii exhibits global distribution. In recent years both the occurrence and dominance of this species, particularly in temperate regions, has increased. Whilst this may be due to increased sensitivity of analytical detection methods or more rigorous sampling routines, it is possible that this expansion has been assisted by a number of changing conditions in these environments. The geographical expansion of both the organism and toxin production can be attributed to phenomena such as eutrophication and climate change. In this review, we discuss the occurrence of C. raciborskii with respect to current literature against the backdrop of increasing global temperatures. Critically, we identify a concerning trend between the geographical spread of this organism and global climate change. © 2011.

Three drinking water storage reservoirs in subtropical southeast Queensland, Australia have regular blooms of the toxic cyanobacterium Cylindrospermopsis raciborskii that can produce cylindrospermopsins. We tested water samples from 16 sites in 3 reservoirs on 2 sampling occasions during a bloom of C. raciborskii in the austral summer and autumn of 2007. Using a range of parameters including quantitative real-time PCR, microscope cell counts and HPLC-MS/MS we correlated the 16S ribosomal RNA gene with total cyanobacteria, the rpoC1 gene with C. raciborskii cell concentrations, and the cyrC gene with cylindrospermopsin concentrations to assess spatial and temporal variability within and between reservoirs. While the correlation between cyrC and cylindrospermopsin cell quotas was good (mean r2 = 0.61 for February samples and 0.75 for March samples), the correlation between total cyanobacteria and the 16S ribosomal RNA gene, and between C. raciborskii and the rpoC1 gene were poor indicating that further work is needed to develop these novel molecular methods. Spatial and temporal analysis of the distribution of rpoC1, cylindrospermopsin cell quotas, and a range of physical and chemical water quality parameters showed the greatest variation occurred between reservoirs, and within the largest and most spatially diverse reservoir. This suggests that populations of C. raciborskii strains with inherently different cylindrospermopsin cell quotas may be an important driver of toxicity in these reservoirs. An outcome of this study was the observation that deoxycylindrospermopsin always exceeded the cylindrospermopsin cell quota by up to 5-fold, and that a peak cell quota of 60 fg (cylindrospermopsin + deoxycylindrospermopsin) cell-1 was measured. Crown Copyright © 2009.

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.

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.

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.

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.

Grinham A.,University of Queensland | Dunbabin M.,CSIRO | Gale D.,Seqwater | Udy J.,Seqwater
Atmospheric Environment | Year: 2011

Accurately quantifying total freshwater storage methane release to atmosphere requires the spatial-temporal measurement of both diffusive and ebullitive emissions. Existing floating chamber techniques provide localised assessment of methane flux, however, significant errors can arise when weighting and extrapolation to the entire storage, particularly when ebullition is significant. An improved technique has been developed that compliments traditional chamber based experiments to quantify the storage-scale release of methane gas to atmosphere through ebullition using the measurements from an Optical Methane Detector (OMD) and a robotic boat. This provides a conservative estimate of the methane emission rate from ebullition along with the bubble volume distribution. It also georeferences the area of ebullition activity across entire storages at short temporal scales. An assessment on Little Nerang Dam in Queensland, Australia, demonstrated whole storage methane release significantly differed spatially and throughout the day. Total methane emission estimates showed a potential 32-fold variation in whole-of-dam rates depending on the measurement and extrapolation method and time of day used. The combined chamber and OMD technique showed that 1.8-7.0% of the surface area of Little Nerang Dam is accounting for up to 97% of total methane release to atmosphere throughout the day. Additionally, over 95% of detectable ebullition occurred in depths less than 12 m during the day and 6 m at night. This difference in spatial and temporal methane release rate distribution highlights the need to monitor significant regions of, if not the entire, water storage in order to provide an accurate estimate of ebullition rates and their contribution to annual methane emissions. © 2011 Elsevier Ltd.

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