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Dr Simon Mitrovic


I have  dual roles as a Senior Research Scientist with the NSW Office of Water and as a Senior Lecturer in The School of the Environment. As an applied scientist focusing on freshwater ecology, environmental flows and plant ecotoxicology part of my role with the Office of Water is to ensure that students are exposed to industry related issues and undertake research relevant to industry needs.


Scientific Committees and editorial boards

  • Core member of the Centre for Environmental Sustainability, UTS
  • Associate Editor for journal Marine and Freshwater Research
  • Member Cold Water Pollution Interagency Committee
  • Member of the NSW State Algal Advisory Group
  • Member eWater Cooperative Research Centre – Project F1 – Impacts of constituents on in-stream processes and food webs
  • Research Affiliate with National University of Singapore (NUS) Raffles Museum of Biodiversity and Research

Professional society memberships

  • International Society for Theoretical and Applied Limnology (SIL)
  • Association of Scientists in Limnology and Oceanography (ASLO)
  • Australian Society for Limnology (ASL)
  • Society for Environmental Toxicology and Chemistry (SETAC)

International Visiting Expert

  • National University of Singapore (NUS) – Biodiversity group. Invited as a phytoplankton expert to consult on program development and sampling design and to develop their skills.
  • Training courses and publication of methods and taxonomy guide for National University of Singapore (NUS).

Image of Simon Mitrovic
Senior Lecturer, School of the Environment
+61 2 9514 8297

Research Interests

  • Freshwater phytoplankton ecology
  • Environmental flows, dissolved organic carbon delivery to rivers and estuaries and ecosystem responses.
  • Cyanobacterial ecology,
  • Harmful algal ecology and factors influencing toxin regulation (marine and freshwater),
  • Benthic algal ecology,
  • Fate and toxicity of algal toxins,
  • Plant ecotoxicology,

Can supervise: Yes

Graduated Honours students

  1. Alec Davie (2005) Nutrients as factors causing diatom blooms in the Hunter River, NSW, UTS.
  2. James Hitchcock (2005-06) Effects of environmental flow delivery of carbon on productivity in the Hunter estuary, UTS.
  3. Daniela Cortez (2009-2010) Longitudinal trends in water quality and macroinvertebrates - Testing the serial discontinuity concept in the Hunter Catchment, UTS.
  4. Grace Corrigan (2013) Effects of light on responses of different phytoplankton communities to nutrient amendment bioassays UTS (With Prof. David Hamilton, Waikato University NZ).
  5. Richard Carney (2013) Bacterial community changes in response to flow events in the Hunter Estuary UTS (With Dr Justin Seymour).
  6. Steven Leahey (2013) Antimony concentrations in waters and sediments of the Bellinger Estuary (With Dr Simon Apte - CSIRO).

Current Honours students

  1. Carla Thomas (2013) Effects of cyanotoxin exposure on higher plants and the synergistic impacts of other stressors

Graduated Masters students

  1. Patrick Stuart (2011) Evaluation of bioretention systems in Manly catchment for water quality improvement and water re-use, UTS.
  2. Doug Westhorpe (2011) Influence of environmental flows in DOC transport to rivers, and roles of DOC in riverine food webs, UTS.

Current Masters Students

  1. Rachel Gray - Effectiveness of thermal pollution mitigation using a novel thermal curtain.

Completed / submitted PhD Students

  1. Alec Davie - The influence of environmental flows on periphyton communities in the Severn River, NSW, UTS. * Submitted.
  2. Stefanie Mueller - Limitation of phytoplankton and sediment release of nutrients in a shallow reservoir, UTS.

Current PhD Students

  1. Ann-Marie Rohlfs - Role of tributary inflows for carbon supply in environmental flow management of the regulated Snowy Mountains Rivers, UTS*
  2. James Hitchcock - The effect of environmental flows and nutrient and carbon inflows on the planktonic foodweb in the Bega River Estuary, UTS.* 
  3. Rebecca Herron – Algae as bioindicators of herbicide pollution in the Great Barrier Reef catchments.UTS *
  4. Maxine Mowe - Cyanobacterial toxins in Singapore’s Reservoirs; identifying progenitor species, toxin production rates and responses to environmental variables, National University of Singapore. 
  5. Ben Woodward – Mobilisation of carbon on soils in the Gwydir River – Griffith University.

* indicates primary supervisor

Journal articles

Zhao, C., Liu, C., Dai, X., Liu, T., Duan, Z., Liu, L. & Mitrovic, S.M. 2015, 'Separation of the impacts of climate change and human activity on runoff variations', Hydrological Sciences Journal, vol. 60, no. 2, pp. 234-246.
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Abstract: A practical approach to separate the impact of the processes of climate change (CC) and human activities (HA) on streamflow is presented. A non-parametric Mann-Kendall-Sneyers test, combined with moving t test and Yamamoto methods, was used to recognize abrupt change points in the runoff time series to determine a baseline period. A new algorithm to separate CC and HA influence on streamflow was deduced based on the climate elasticity concept. Application to the Chao River, China, shows that CC imposed a positive impact on streamflow in this region (25%, on average), while HA exerted a continuous negative impact of 75% in the period after the 1950s. These results are of great use in understanding the variation of CC and HA impacts under different human development patterns.
Zhao, C.S., Yang, S.T., Liu, C.M., Dou, T.W., Yang, Z.L., Yang, Z.Y., Liu, X.L., Xiang, H., Nie, S.Y., Zhang, J.L., Mitrovic, S.M., Yu, Q. & Lim, R.P. 2015, 'Linking hydrologic, physical and chemical habitat environments for the potential assessment of fish community rehabilitation in a developing city', Journal of Hydrology, vol. 523, pp. 384-397.
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Aquatic ecological rehabilitation is increasingly attracting considerable public and research attention. An effective method that requires less data and expertise would help in the assessment of rehabilitation potential and in the monitoring of rehabilitation activities as complicated theories and excessive data requirements on assemblage information make many current assessment models expensive and limit their wide use. This paper presents an assessment model for restoration potential which successfully links hydrologic, physical and chemical habitat factors to fish assemblage attributes drawn from monitoring datasets on hydrology, water quality and fish assemblages at a total of 144 sites, where 5084 fish were sampled and tested. In this model three newly developed sub-models, integrated habitat index (. IHSI), integrated ecological niche breadth (. INB) and integrated ecological niche overlap (. INO), are established to study spatial heterogeneity of the restoration potential of fish assemblages based on gradient methods of habitat suitability index and ecological niche models. To reduce uncertainties in the model, as many fish species as possible, including important native fish, were selected as dominant species with monitoring occurring over several seasons to comprehensively select key habitat factors. Furthermore, a detrended correspondence analysis (DCA) was employed prior to a canonical correspondence analysis (CCA) of the data to avoid the "arc effect" in the selection of key habitat factors. Application of the model to data collected at Jinan City, China proved effective reveals that three lower potential regions that should be targeted in future aquatic ecosystem rehabilitation programs. They were well validated by the distribution of two habitat parameters: river width and transparency. River width positively influenced and transparency negatively influenced fish assemblages. The model can be applied for monitoring the effects of fish assemblage res...
Growns, I., Chessman, B., Mitrovic, S. & Westhorpe, D. 2014, 'The effects of dams on longitudinal variation in river food webs', Journal of Freshwater Ecology, vol. 29, no. 1, pp. 69-82.
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We examined the effects of two dams on longitudinal variation of riverine food webs using stable isotope and gut contents analyses along four rivers in the Hunter Valley in eastern Australia. Longitudinal 15N enrichment was observed in most invertebrate taxa and food sources but significant longitudinal variation was rare for 13C, and composition of gut contents of invertebrate taxa did not vary significantly with longitudinal position. Most invertebrates and food sources were more 15N-enriched at sites immediately downstream of the dams than expected from their upstream longitudinal position, a result not mirrored by gut contents and 13C. Enrichment of 15N downstream may be attributed to altered water quality as a result of impoundment but further research is necessary to elucidate whether physico-chemical riverine processes or trophic mechanisms are responsible. Our observations regarding the influence of dams on isotope ratios are contrary to the few existing studies, suggesting the small volumes relative to annual inflows of dams in the present study limit downstream impacts by maintaining aspects of flow variability. 2013 2013 Taylor & Francis.
Jardine, T.D., Hadwen, W.L., Hamilton, S.K., Hladyz, S., Mitrovic, S.M., Kidd, K.A., Tsoi, W.Y., Spears, M., Westhorpe, D.P., Fry, V.M., Sheldon, F. & Bunn, S.E. 2014, 'Understanding and overcoming baseline isotopic variability in running waters', River Research and Applications, vol. 30, no. 2, pp. 155-165.
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Natural abundances of stable isotopes in lotic food webs yield valuable information about sources of organic matter for consumers and trophic structure. However, interpretation of isotopic information can be challenging in the face of variability in organisms at the base of food webs. Unionid and dreissenid mussels, commonly used as baseline organisms in lakes, are uncommon in many river settings and can have variable diets, thus making them unsuitable as a universal baseline for many river food web studies and often forcing reliance on more common benthic insects for this purpose. Turnover rates of body carbon and nitrogen in insects are relatively rapid (1 to 50days half-life). These rapid turnover rates in primary consumers can result in considerable temporal variability in ?13C that rivals that of algae (>10 range within a site). This suggests that using primary consumers as a surrogate baseline for algae may not circumvent the problem of temporal variability and the resultant mismatch of sources with longer-lived, slow-growing secondary and tertiary consumers. There are several strategies for reducing the influence of these confounding factors when bivalves with a known diet are not present. These include sampling over large spatial scales and correlating ?13C of consumers with the source of interest (e.g. benthic algae), sampling baseline organisms multiple times in the weeks preceding sampling of larger consumers (particularly in response to large changes in discharge) and using algal-detrital separation methods and multiple tracers as much as possible. Incorporating some of these recommendations and further exploring variability at the base of the food web will potentially provide greater insights into consumer-resource coupling in running waters and more robust conclusions about food web structure and energy flow in these dynamic systems. 2012 John Wiley & Sons, Ltd.
Wood, R.J., Mitrovic, S.M. & Kefford, B.J. 2014, 'Determining the relative sensitivity of benthic diatoms to atrazine using rapid toxicity testing: A novel method', Science of the Total Environment, vol. 485-486, no. 1, pp. 421-427.
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Herbicides pose a potential threat to aquatic ecosystems, especially to phototrophic organisms such as benthic diatoms. Benthic diatoms may be a valuable indicator of the toxic impacts of herbicides in aquatic systems. However, this requires information on the herbicide sensitivity of a wide range of freshwater benthic diatom taxa. Unfortunately this information is only available for a limited number of species as current methods of developing new algae toxicity tests on individual taxa are lengthy and costly. To address this issue, we developed a new rapid toxicity test method to test natural benthic communities, from which the relative herbicide sensitivity of many individual taxa can be derived. This involved the collection of natural benthic communities from rocks in situ, which were placed directly into laboratory toxicity tests. Sensitivity data for several diatom genera in a 48hour exposure toxicity test were produced, without the need for cultures or multiple site visits. After exposure to the highest treatment of atrazine (500?gL-1) there were significant declines of healthy cells in the most sensitive genera: Gomphonema declined by 74%, Amphora by 62%, Cymbella by 54% and Ulnaria by 34% compared to control levels. In contrast, the genera, Eunotia, Achnanthidium and Navicula, had no statistically significant decline in cell health. This method can identify the diatom taxa most at risk of herbicide toxicity within the natural benthic diatom community. The rapid toxicity testing method presented is a simple and effective method to obtain sensitivity data for multiple taxa within a natural benthic diatom community in a relatively short period of time. 2014 Elsevier B.V.
Griffin, C.T., Mitrovic, S., Danaher, M. & Furey, A. 2014, 'Development of a fast isocratic LC-MS/MS method for the high-throughput analysis of pyrrolizidine alkaloids in Australian honey.', Food Addit Contam Part A Chem Anal Control Expo Risk Assess.
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Honey samples, originating from Australia, were purchased and analysed for targeted pyrrolizidine alkaloids (PA) using a new and rapid isocratic LC-MS/MS method. This isocratic method was developed from, and is comparable to, a gradient elution method and resulted in no loss of sensitivity or reduction in chromatographic peak shape. Isocratic elution allows for significantly shorter run times (6min), eliminates the requirement for column equilibration periods and thus has the advantage of facilitating a high-throughput analysis which is particularly important for regulatory testing laboratories. In excess of two hundred injections are possible, with this new isocratic methodology, within a 24 hour period which is a>50% improvement on all previously published methodologies. Good linear calibrations were obtained for all ten PAs and four pyrrolizidine alkaloid N-oxides (PANOs) in spiked honey samples (3.57-357.14gL(-1); R(2)?0.9987). Acceptable inter-day repeatability was achieved for the target analytes in honey with % RSD values (n=4) less than 7.4%. Limits of detection (LOD) and limits of quantitation (LOQ) were achieved with spiked PAs and PANOs samples; giving an average LOD of 1.6gkg(-1) and LOQ of 5.4gkg(-1). This method was successfully applied to Australian and New Zealand honey samples sourced from supermarkets in Australia. Analysis showed that 41 of the 59 honey samples were contaminated by PAs with the mean total sum of PAs being 153gkg(-1). Echimidine and lycopsamine were predominant and found in 76% and 88%, respectively, of the positive samples. The average daily exposure, based on the results presented in this study, were 0.051gkg(-1)bwday(-1) for adults and 0.204gkg(-1)bwday(-1) for children. These results are a cause for concern when compared with the proposed EFSA (European Food Safety Authority), COT (Committee on Toxicity) and BfR (Bundesinstitut fr Risikobewertung - the Federal Institute of Risk Assessment German...
Hitchcock, J.N. & Mitrovic, S.M. 2014, 'Highs and lows: The effect of differently sized freshwater inflows on estuarine carbon, nitrogen, phosphorus, bacteria and chlorophyll a dynamics', Estuarine, Coastal and Shelf Science.
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Freshwater inflows play a key role in the delivery of organic carbon to estuaries. However, our understanding of the dynamics between discharge and carbon globally is limited. In this study we performed a 30-month monitoring study on the Bega and Clyde River estuaries, Australia, to understand the influence that discharge had on carbon, nitrogen, phosphorus, bacteria and chlorophyll a dynamics. We hypothesised that 1) discharge would be the most important factor influencing carbon and nutrient concentrations, though during low flows chlorophyll a would also be positively related to carbon, 2) bacteria would be related to dissolved organic carbon (DOC), and chlorophyll a to temperature, nitrogen and phosphorus, and 3) that concentrations of carbon, nitrogen, phosphorus, bacterial biomass and chlorophyll a would be significantly different between large 'flood flows', smaller 'fresh flows' and base flow conditions. We found that discharge was always the most important factor influencing carbon and nutrient concentrations, and that primary production appeared to have little influence on the variation in DOC concentration even during base flow conditions. We suggest this relationship is likely due to highly episodic discharge that occurred during the study period. Bacteria were related to DOC in the lower estuary sites, but phosphorus in the upper estuary. We suggest this is likely due to the input of bioavailable carbon in the upper estuary leading bacteria to be P limited, which changes downstream to carbon limitation as DOC becomes more refractory. Chlorophyll a was positively related to temperature but not nutrients, which we suggest may be due to competition with bacteria for phosphorus in the upper estuary. Carbon, nitrogen and phosphorus concentrations were different under flood, fresh and base flow conditions, though these differences sometimes varied between estuary locations for different resources. Overall, the results demonstrate that discharge plays an im...
Mller, S. & Mitrovic, S.M. 2014, 'Phytoplankton co-limitation by nitrogen and phosphorus in a shallow reservoir: progressing from the phosphorus limitation paradigm', Hydrobiologia, vol. 744, no. 1, pp. 255-269.
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Phosphorus (P) limitation has been regarded as the rule in freshwater systems and the basis for phytoplankton growth management. We hypothesised that P would be the limiting nutrient for phytoplankton growth in Grahamstown Dam, a shallow, mesotrophic reservoir, across different seasons and on different experimental time scales. Seven fully factorial microcosm assays with additions of nitrogen (N) and P were conducted in situ during different seasons. The influence of longer experimental duration was examined in two 18-day mesocosm assays. Additions of N and P in combination evoked significantly higher phytoplankton biomass and biovolumes of individual algal genera compared with controls and other treatments in both types of experiment. There were some significant responses to P additions in the microcosm assays in winter. Some genera first responded to combined P and N addition and then to P only addition during the mesocoms assays. Our results show that P was not the limiting nutrient across all seasons but that phytoplankton was mostly co-limited by N and P. A longer experimental time scale did not change this outcome at the biomass level. This implies that input of N as well as of P should be considered in the management of phytoplankton growth.
Davie, A.W. & Mitrovic, S.M. 2014, 'Benthic algal biomass and assemblage changes following environmental flow releases and unregulated tributary flows downstream of a major storage', Marine and Freshwater Research, vol. 65, no. 12, pp. 1059-1071.
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A large dam reducing the magnitude of flows regulates the Severn River, Australia. Environmental flows (EFs) are designed to increase the magnitude of flow and improve ecological outcomes such as reducing filamentous algal biomass and re-setting algal succession. The effectiveness of EF releases to alter benthic algal assemblages is poorly understood. We examined benthic algal biomass and assemblage structure at two cobble-dominated riffle sites downstream of Pindari Dam, before and after two EFs. Both EFs had discharges of ?11.6m3 s-1 (velocity of ?0.9ms -1). Neither EF reduced benthic algal biomass, and sometimes led to increases, with density of some filamentous algae increasing (Stigeoclonium and Leptolyngbya). An unregulated flow from a tributary between the two sites increased discharge to 25.2m3 s-1 (velocity of ?1.2ms-1), decreasing biomass and density of filamentous algae. The similarity in flow velocities between scouring and non-scouring events suggests that thresholds may exist and/or suspended sediments carried from unregulated tributaries may contribute to reduce algal biomass. Identifying velocities needed to reduce algal biomass are useful. Accordingly, EFs with flow velocities ?1.2ms-1 may achieve this in river cobble-dominated riffle sections dominated by filamentous algae. Lower flow velocities of <0.9ms-1 may result in no change or an increase in filamentous algae.
Hitchcock, J.N. & Mitrovic, S.M. 2013, 'Different resource limitation by carbon, nitrogen and phosphorus between base flow and high flow conditions for estuarine bacteria and phytoplankton', Estuarine, Coastal and Shelf Science, vol. 135, pp. 106-115.
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Freshwater inflows can deliver substantial inputs of allochthonous organic carbon to estuaries. The role that allochthonous DOC has on structuring bacterial and phytoplankton communities is still not well understood. We performed a series of 1.25L bioassay limitation experiments on the Bega and Clyde River estuaries in NSW, Australia, examining what resources limit bacteria and phytoplankton growth. We hypothesized that during base flow conditions bacteria would be carbon limited, and after high flow conditions they would be nutrient limited. A full factorial design was used with additions of carbon (glucose), nitrogen (KNO3) and phosphorus (KH2PO4). During the experiments that took place during base flow conditions bacteria were always primarily C-limited. After high flow conditions, bacteria were P-limited on the Clyde River, and remained C-limited on the Bega River. Phytoplankton growth was limited at all times in each estuary, tending toward N-limitation on the Bega River and P-limitation on the Clyde river. During high flow conditions on the Clyde River, when bacteria and phytoplankton were both primarily P-limited, it appeared that bacteria was able to outcompete phytoplankton for nutrients. These results suggest that freshwater inflows and allochthonous DOC maybe important in structuring estuarine microbial ecosystems and individual estuaries may behave differently in terms of their limiting resources. 2013 Elsevier Ltd.
Zhao, C.S., Liu, C.M., Sun, Y., Yang, G., Mitrovic, S.M. & Wang, H. 2013, 'Heterogeneity of water quality in Huai River, China by using bio-monitoring data', Water Science and Technology: Water Supply, vol. 13, no. 6, pp. 1524-1533.
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A new approach by combining bioindicators (BiI) and biotic indices (BIs) for evaluating water quality is presented in this paper. It is then applied to the Huai River Basin (HRB), China, which is well-known globally for its heavy anthropogenic influences. Results indicate that the spatial distribution of BI-indicated water quality has roughly the same pattern as that shown by BiI, but the pollution level using BI was, on average, greater than that by BiI; the northern plain area has a degraded water quality (ranging from 'a-mesosaprobic' to 'a-polysaprobic' in a wet season) while the southern mountain area and the southern part of the East Line of the South-North Water Transfer Project has a better water quality ('?-mesosaprobic'). Water quality is worse in the dry season than in the wet season. We concluded that zoobenthos and zooplankton are more reliable indicators of water quality; biological indices are more sensitive to water quality but less reliable than BiI. These results will be of use in the ecological restoration of the Huai River and benefit water resource management in HRB in the future. IWA Publishing 2013 Water Science and Technology: Water Supply.
Cortez, D.P., Growns, I.O., Mitrovic, S.M. & Lim, R.P. 2012, 'Effects of a gradient in river regulation on the longitudinal trends in water quality and benthic algal and macroinvertebrate assemblages in the Hunter River, Australia', Marine and Freshwater Research, vol. 63, no. 6, pp. 494-504.
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River regulation impacts lotic ecosystem processes; however, the effect of a gradient of regulation on these attributes has rarely been studied. This study examined the effects of a river regulation gradient on longitudinal trends in water quality and benthic algal and macroinvertebrate assemblages in three tributaries of the Hunter River, New South Wales, Australia. Longitudinal patterns were expected to differ across rivers, with recovery being proportional to its regulation gradient. Significant differences in longitudinal trends were tested using permutational multivariate analysis of variance (PERMANOVA) through exploration of the river by distance from source interaction. Multi-dimensional scaling (MDS) ordination plots identified sites responsible for any significant interaction observed. Similarity percentage analysis (SIMPER) analyses identified variables/taxa responsible for differences at sites below dams. BEST analyses identified environmental variables best explaining biological assemblage patterns. Significant differences in longitudinal trends were observed for all attributes. Increases in the regulation gradient most affected macroinvertebrate assemblages, followed by water quality and benthic algal assemblages respectively. Downstream recovery was absent in the heavily regulated river at its most downstream site, whereas recovery was observed on corresponding sites of the moderately regulated river. The study suggests that a gradient in river regulation increases the magnitude of disruption of lotic ecosystems, with recovery dependent on this gradient. 2012 CSIRO.
Westhorpe, D.P. & Mitrovic, S.M. 2012, 'Dissolved organic carbon mobilisation in relation to variable discharges and environmental flows in a highly regulated lowland river', Marine and Freshwater Research, vol. 63, no. 12, pp. 1218-1230.
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The relationships between discharge and dissolved organic carbon (DOC) have been extensively studied in rainfall runoff-driven stream systems. Less is known about discharge and DOC relationships in river systems dependent on floodplain inundation. We examined DOC dynamics and mobilisation over low discharge periods and several larger discharge events in the highly regulated lowland Namoi River, Australia. Stable isotope signatures (? 13C) of various water-column fractions (e.g. 200?m, fine particulate organic matter) were used to determine the sources of DOC. DOC concentrations over low discharge periods were fairly similar among sites and ranged between 5 and 10mgL-1. Concentrations during a high-discharge event increased substantially with a mean of 20.4mgL-1 and a maximum of 44mgL-1. Significant positive linear relationships were found between DOC concentrations and discharge (P<0.001, r2?0.45). The 13C composition of DOC sampled across the three sites (e.g.-26.2) suggests a mixture of terrestrial and aquatic sources, with little downstream variation; however, we would envisage that during periods of high discharge allochthonous sources would dominate. Environmental flows (that are ecologically beneficial, potentially reversing changes brought about by flow regulation) have been allocated to the river, with the intention to increase the amount of DOC delivered to the river. The relationship between DOC and discharge was used to estimate DOC loads to the river under different modelled flow-management scenarios, including without environmental flow, with environmental flow, and simulated natural (low development) flow. On the basis of the modelling results, environmental flows should increase the amount of allochthonous DOC transported within the river in years with moderate and large flow events. Years with low flows did not deliver large loads of allochthonous DOC. The present results showed the potential variability in DOC delivery in relation to floodplain ...
Roelke, D.L., Spatharis, S. & Mitrovic, S.M. 2012, 'A new hydrology: Effects on ecosystem form and functioning', Canadian Journal of Fisheries and Aquatic Sciences, vol. 69, no. 8, pp. 1377-1379.
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Water cycles are changing because of human population growth and climate change. Such changes will affect fundamental system-level characteristics that in turn will greatly influence ecosystem form and functioning. Here, a collection of papers is offered that furthers our understanding of cause and effect relationships between altered hydrology and various ecosystem properties. Combined, these papers address issues related to inflows, connectivity, and circulation and vertical mixing. In regards to altered inflows, this collection of papers addresses how seagrass bed communities, incidence of some haptophyte harmful algal blooms, and biodiversity of intermittently flowing streams might respond. These papers also address factors that influence connectivity in wetlands, and in the case of a lake and its neighboring wetland, how connectivity between systems can profoundly affect ecosystem form and functioning. Finally, the effects of altered circulation and vertical mixing are addressed as they relate to the spread of some cyanobacteria blooms to higher latitudes. The reader of this collection of papers gains a better appreciation of how ecosystem form and functioning is influenced by hydrologic processes and can conclude that there is a need for continued research in this area to better understand the impacts of human population growth and climate change.
Westhorpe, D.P., Mitrovic, S.M. & Woodward, K.B. 2012, 'Diel variation of dissolved organic carbon during large flow events in a lowland river', Limnologica, vol. 42, no. 3, pp. 220-226.
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Diel variation in dissolved organic carbon (DOC) within lotic systems has been reported on numerous occasions. However, to our knowledge there has been no published work on diel DOC variation within lowland rivers during high flow events. We sampled DOC at 4h intervals from two sites across two distinct flow regimes in the regulated lower Namoi River, Australia. This included a large flood (mean flow 224m 3s -1 and a peak flow of 376m 3s -1) sampled every 4h for 10 consecutive days. DOC concentrations were significantly greater at night than during the day (P<0.05) and the mean DOC concentration was 23.4mgL -1 at night compared to 18.9mgL -1 during daylight hours. The magnitude and duration of flow within this lowland river system and the mobilisation of large quantities of allochthonous carbon appeared to play a role in increasing DOC concentration and the diel difference. 2012.
Davie, A.W., Mitrovic, S.M. & Lim, R.P. 2012, 'Succession and accrual of benthic algae on cobbles of an upland river following scouring', Inland Waters, vol. 2, no. 2, pp. 89-100.
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Flow releases from dams can be used to scour benthic algae, simulating the effects of natural spates and maintaining benthic algae in an early successional stage for increased grazer palatability. The timing of releases needs to consider the natural periodicity of flow events and the speed of regrowth and community succession changes. We studied benthic algal regrowth and succession using manipulative field experiments during summer and winter in the upland regulated Severn River, New South Wales, Australia. Benthic algal biomass accrual as chlorophyll a and community changes were determined after artificially scoured cobbles were returned to the river. In summer, algal biomass and diversity on scoured cobbles took 2 weeks to return to levels similar to reference cobbles and 5 weeks in winter. Chlorophyll a during summer was initially 0.24 0.06 mg m-2 on scoured cobbles, but by day 16 had increased to 9.74 1.97 mg m-2 and was no longer significantly different from reference cobbles. In winter, chlorophyll a was initially 0.47 0.13 mg m-2 on scoured cobbles, but by day 37 had increased to 44.7 10.9 mg m-2 and was no longer significantly different from reference cobbles. Peak chlorophyll a accrual during summer and winter was 1.64 and 2.63 mg m-2 d-1, respectively. Early succession in both experiments was dominated by diatoms such as Cocconeis, Synedra, and Fragilaria. A proliferation of the filamentous green alga Stigeoclonium was indicative of a late succession community. The implications for flow management based on resetting of benthic algae by scouring in riffle reaches of rivers are discussed. International Society of Limnology 2012.
Mitrovic, S.M., Lorrainehardwick & Forughdorani 2011, 'Use of flow management to mitigate cyanobacterial blooms in the Lower Darling River, Australia', Journal of Plankton Research, vol. 33, no. 2, pp. 229-241.
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The growth of planktonic cyanobacteria in a weir pool on the Lower Darling River, Australia, downstream of the major regulated Menindee Lake system was examined. Blooms of the saxitoxin producing freshwater cyanobacterium Anabaena circinalis occurred for two summers out of four studied. Large cell numbers of other cyanobacteria including Aphanizomenon, Planktolyngbya and Merismopedia also occurred during the same summer periods as the Anabaena blooms. The growth events also coincided with periods of improved light climate. Flow releases from the regulated Menindee Lakes System were assessed for their ability to either suppress bloom development or to mitigate pre-existing blooms over this period. A discharge of 300 ML/day (flow velocity of 0.03 m/s) was found to be sufficient to prevent prolonged periods of persistent thermal stratification, which also suppressed the development of A. circinalis blooms. A flow release of 3000 ML/day was effective at removing an established cyanobacterial bloom, and total cyanobacterial numbers declined from over 100 000 to <1000 cells/mL within a week. In two summers without blooms, higher flows and decreased light availability prevented the development of cyanobacterial blooms. Flow releases were effective at mitigating cyanobacterial growth through either the suppression of persistent thermal stratification or through dilution and translocation of cells. Greater discharges also increased turbidity, which diminished the growth of cyanobacteria through reduced light availability under the mixed conditions, which also reduced the ability for surface migration through buoyancy regulation. The volume of water required for different management strategies varied and is considered in terms of environmental allocations. The Author 2010.
Mitrovic, S.M., Hitchcock, J.N., Davie, A.W. & Ryan, D.A. 2010, 'Growth responses of Cyclotella meneghiniana (Bacillariophyceae) to various temperatures', Journal of Plankton Research, vol. 32, no. 8, pp. 1217-1221.
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The growth of Cyclotella meneghiniana was examined at temperatures between 13 and 28C at 3C intervals. Growth increased linearly with temperature to a growth maximum at 25C, with growth decreasing at 28C. The Author 2010.
Hitchcock, J.N., Mitrovic, S.M., Kobayashi, T. & Westhorpe, D.P. 2010, 'Responses of estuarine bacterioplankton, phytoplankton and zooplankton to dissolved organic carbon (DOC) and inorganic nutrient additions', Estuaries and Coasts, vol. 33, no. 1, pp. 78-91.
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The response of planktonic bacteria and phytoplankton to various additions of dissolved organic carbon (DOC) as glucose, with and without inorganic nutrients (nitrogen and phosphorus), was tested in the upper to mid Hunter Estuary, Australia. In situ microcosms (1.25 L) were performed at two sites with varying salinities over three seasons. Analysis of variance showed a significant difference among control and treatments for all seasons for the bacterial, dissolved oxygen and chlorophyll a responses (P < 0.05). A significant interaction between treatment and site was found in autumn for dissolved oxygen, autumn and spring for bacterial and spring for chlorophyll a responses. At both sites for each season, and on nearly all occasions, bacterial surface area was enhanced by DOC addition as indicated by both increased bacterial abundance and dissolved oxygen utilisation. DOC in combination with inorganic nutrients sometimes further enhanced the bacterial response compared to DOC alone. Inorganic nutrients alone did not enhance growth of the heterotrophic bacterioplankton. Addition of DOC alone led to decreased chlorophyll a relative to the control, probably due to competition for limited inorganic nutrients with the bacterioplankton DOC non-limiting conditions. Results suggest that the heterotrophic community was limited by DOC at both sites and across seasons. An experiment with a larger volume (70 L), performed over a longer time, compared a control with DOC addition. Increased bacterial biomass as a result of DOC addition occurred at day 2. Chlorophyll a did not significantly differ between treatments. An increase in zooplankton density was recorded in the DOC treatment relative to the control at day 10. This study supports the contention that increased DOC delivery with river inflows through environmental flow allocations will stimulate heterotrophic bacterioplankton production in the upper Hunter Estuary. Coastal and Estuarine Research Federation 2009.
Oliver, R.L., Mitrovic, S.M. & Rees, C. 2010, 'Influence of salinity on light conditions and phytoplankton growth in a turbid river', River Research and Applications, vol. 26, no. 7, pp. 894-903.
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A turbid lowland river in Australia was studied to describe factors influencing the light conditions for phytoplankton growth. Vertical attenuation coefficients correlated with nepholometric turbidity enabling estimation of euphotic depths (z eu) from long term turbidity monitoring. Light conditions were assessed from the ratio of z eu to the maximum water depth (z m). Predominantly z eu/z m ratios were below 0.2, a value indicating the minimum light conditions required to support phytoplankton growth. A transitional state with z eu/z m between 0.2 and 0.35 occurred 15% of the time, while light sufficiency occurred for 30% of the time. Peaks in eukaryotic phytoplankton biomass developed when z eu/z m was at or above transitional values. Large increases in cyanobacterial numbers (Anabaena sp.) only occurred when z eu/z m exceeded 0.35. Turbidity increased quickly with elevated flows but did not decline substantially as flows reduced and light limiting conditions extended into low flow periods otherwise conducive to phytoplankton growth. However, during extended periods of reduced flows conductivity increased causing a substantial reduction in turbidity with concomitant improvements in light penetration. A turbidity of ca. 100 NTU marked the transition to light sufficiency at the study site and occurred at a conductivity of ca. 300?Scm -1 demonstrating that small changes in salinity can have major effects on light penetration. These results show that flow, salinity and turbidity all play a part in determining the growth conditions for phytoplankton in turbid rivers. 2009 John Wiley & Sons, Ltd.
Hadwen, W.L., Fellows, C.S., Westhorpe, D.P., Rees, G.N., Mitrovic, S.M., Taylor, B., Baldwin, D.S., Silvester, E. & Croome, R. 2010, 'Longitudinal trends in river functioning: Patterns of nutrient and carbon processing in three Australian rivers', River Research and Applications, vol. 26, no. 9, pp. 1129-1152.
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Understanding longitudinal trends in the processing of carbon in rivers represents a much conceptualised, but infrequently tested, issue in aquatic ecology. In this study, we conducted concurrent longitudinal examinations of three very different rivers in eastern Australia to determine whether general principles in river functioning exist across broad geographic and hydrologic scales. Specifically, we examined trends in ambient basic water chemistry, nutrient concentrations, dissolved organic carbon (DOC), extracellular enzymes and food web structure and functioning and conducted bioassays to examine the degree to which DOC and nutrients limit heterotrophic bacterial respiration. These parameters revealed striking similarities across all sites. For metazoan communities, stable isotope analysis showed that algal carbon was the dominant basal resource utilised by consumers in all three rivers, suggesting that in-stream primary producers strongly underpin trophic pathways regardless of the position within a catchment or catchment condition. Analyses of extracellular enzymes revealed that microbial communities are actively utilising DOC at all sites. In fact, heterotrophic microbial respiration was strongly limited by DOC at all sites, with nutrient additions resulting in only relatively minor increases in respiration. Ultimately, this study demonstrates that DOC and algal carbon are critically important drivers of ecosystem processes in Australian riverine ecosystems. Furthermore, across all of our sites and rivers, ambient nutrient concentrations did not influence carbon processing. The consistent longitudinal trends in river function identified in this study provide useful insights for catchment managers and modellers with respect to identifiying key principles that underpin ecosystem functioning in Australian rivers. Copyright 2009 John Wiley & Sons, Ltd. Copyright 2009 John Wiley & Sons, Ltd.
Westhorpe, D.P., Mitrovic, S.M., Ryan, D. & Kobayashi, T. 2010, 'Limitation of lowland riverine bacterioplankton by dissolved organic carbon and inorganic nutrients', Hydrobiologia, vol. 652, no. 1, pp. 101-117.
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Flow regulation in lowland rivers has reduced the amount of allochthonous dissolved organic carbon (DOC) entering main channels through less frequent wetting of benches, flood runners and floodplains. The hypothesis tested was that lowland riverine bacterioplankton are DOC limited when flow events are absent and simulating an increase in assimilable DOC similar to that expected during an environmental flow will lead to heterotrophic dominance. Experiments took place in the Namoi River, a highly regulated lowland river in Australia. Specifically, in situ microcosms were used to examine the responses of bacterioplankton and phytoplankton to various additions of DOC as glucose or leaf leachate, with and without additions of inorganic nutrients. The results indicated that ambient DOC availability limited the bacterioplankton for the three seasons over which we conducted the experiments. When DOC was added alone, dissolved oxygen concentrations decreased primarily because of increased bacterial respiration and bacterioplankton growth generally increased relative to controls. Additions of DOC alone led to a pattern of decreased chlorophyll a concentration relative to controls, except for willow leachate. Additions of inorganic nutrients alone increased chlorophyll a concentrations above controls, indicating limitation of phytoplankton. These findings support our hypothesis. Based on the present results, environmental flows should increase the duration of allochthonously driven heterotrophic dominance, thus shifting regulated lowland rivers to more natural (pre-regulation) conditions for greater periods. 2010 Springer Science+Business Media B.V.
Chessman, B.C., Westhorpe, D.P., Mitrovic, S.M. & Hardwick, L. 2009, 'Trophic linkages between periphyton and grazing macroinvertebrates in rivers with different levels of catchment development', Hydrobiologia, vol. 625, no. 1, pp. 135-150.
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Stable isotope signatures (?13C and ?15N) were used to compare trophic linkages between epilithic periphyton and three families of macroinvertebrates (Baetidae, Leptophlebiidae and Gripopterygidae) in riffles of two rivers with developed catchments (including agriculture, urbanization, impoundment and flow regulation) and two with undeveloped catchments (native forest with no major impoundments) in the Murrumbidgee River system, New South Wales, Australia. Periphyton had much higher average ?15N values and lower average C:N ratios in the developed rivers than in the undeveloped rivers, probably because of the combined effects of nutrient enrichment, upstream impoundment and alteration of riparian vegetation. The invertebrates were generally slightly depleted in 13C and 15N relative to expected values if they were assimilating whole periphyton alone, which suggests that they were assimilating periphyton components selectively or also consuming other foods. The match in isotope signatures between periphyton and invertebrates was only slightly weaker in the developed than in the undeveloped rivers, suggesting that development did not greatly disrupt trophic linkages between periphyton and these invertebrates. 2009 Springer Science+Business Media B.V.
Mitrovic, S.M., Chessman, B.C., Davie, A., Avery, E.L. & Ryan, N. 2008, 'Development of blooms of Cyclotella meneghiniana and Nitzschia spp. (Bacillariophyceae) in a shallow river and estimation of effective suppression flows', Hydrobiologia, vol. 596, no. 1, pp. 173-185.
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Diatom blooms in the middle reaches of the shallow, freshwater, Hunter River, Australia, are a frequent nuisance to river users. During a 4-year study, blooms of Cyclotella meneghiniana and Nitzschia spp. coincided with water temperatures above 23C and flows below 400 Ml d-1 that lasted for more than 12 days. Redundancy analysis showed that water temperature was positively related, and antecedent flow was negatively related, to the abundance of both taxa. Addition experiments indicated that nutrients are seldom limiting to growth. It is suggested that a combination of faster growth rates at higher temperatures and longer retention times at low flows allows bloom populations to develop. Simulation modelling showed that flow regulation and water extraction have decreased flows in the river during summer, and consequently have probably increased the number of diatom blooms. Environmental flows have been provided to the river, but are not sufficient to prevent blooms. Discharges required for bloom suppression are described. 2007 Springer Science+Business Media B.V.
Ryan, N.J., Mitrovic, S.M. & Bowling, L.C. 2008, 'Temporal and spatial variability in the phytoplankton community of Myall Lakes, Australia, and influences of salinity', Hydrobiologia, vol. 608, no. 1, pp. 69-86.
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The variability in the phytoplankton communities of the Myall Lakes, a series of four interconnected coastal lakes on the lower north coast of New South Wales, was studied between 1999 and 2002. There was considerable spatial variability across the lake system. Bombah Broadwater experienced blooms of Anabaena in 1999 and early 2000, but these were replaced from late 2000 onwards by Chroococcus and a variety of eukaryotic taxa, particularly flagellates and diatoms. In comparison, the phytoplankton community of Myall Lake was dominated for much of the study period by Chroococcus, Merismopedia and chlorophyte taxa. The sites located midway between these two main lakes represent an ecotone, with elements of the phytoplanktonic flora of both main lakes being present. Changes in phytoplankton community composition in Bombah Broadwater occurred fairly frequently. In contrast, the phytoplankton community in Myall Lake changed little during the course of the study and can be considered as being at long-term equilibrium. The reasons for this lie in the morphology and hydrology of the lake system, which in turn create gradients in a number of physico-chemical water quality attributes. Bombah Broadwater is influenced by episodic and stochastic freshwater inflows from the upper Myall River catchment, and in times of drought by saline marine incursions via the lower Myall River. Myall Lake however represents a cul-de-sac, with only a small hydraulic connection to the remainder of the lake system. As it has little input from its small catchment, the limnological conditions within this lake remain relatively constant for long periods of time. Although no patterns of seasonal succession were discernable in any of the lakes, some longer-term (annual) changes did occur, and certain taxa displayed enhanced growth in summer. Salinity was found to be an important factor in determining phytoplankton community composition and abundance. Canonical Correspondence Analysis of phytoplankton...
Mitrovic, S.M., Chessman, B.C., Bowling, L.C. & Cooke, R.H. 2006, 'Modelling suppression cyanobacterial blooms by flow management in a lowland river', River Research and Applications, vol. 22, no. 1, pp. 109-114.
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Growth and dominance of the cyanobacterium Anabaena circinalis in weir pools of the Barwon-Darling River, Australia, are related to persistent vertical thermal stratification between October and March, when discharge is low. We determined critical velocities and discharges required to suppress bloom formation at three sites, and modelled the occurrence of sub-critical discharges in order to predict the frequency of blooms under different management scenarios. Our model suggests that the frequency of blooms was about double that expected under near-natural flows (without major impoundment or water extraction) for 1990-2000. Flow management, through Environmental Water Provisions that limit water extraction when river levels are low, has been in place since July 2000. Our model suggests that these provisions are unlikely to have had an effect on bloom frequency for 2000-2003. In the longer term, however, they could reduce bloom frequency at some sites by up to one-third. Copyright 2005 John Wiley & Sons, Ltd.
Mitrovic, S.M., Allis, O., Furey, A. & James, K.J. 2005, 'Bioaccumulation and harmful effects of microcystin-LR in the aquatic plants Lemna minor and Wolffia arrhiza and the filamentous alga Chladophora fracta', Ecotoxicology and Environmental Safety, vol. 61, no. 3, pp. 345-352.
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Although the toxic effects of cyanotoxins on animals have been examined extensively, little research has focused on their effects on higher plants and macroalgae, and the potential for bioaccumulation in the food web through plants. Two aquatic plants, Lemna minor and Wolffia arrhiza, and one filamentous alga, Chladophora fracta, were exposed to the cyanotoxin microcystin-LR. Growth of L. minor (as weight and frond number) and root length were significantly reduced and peroxidase activity was significantly increased after 5 days of exposure to concentrations of 10 and 20 ?g mL-1 microcystin-LR. Growth of W. arrhiza (as frond number) was significantly reduced after 5 days of exposure to 15 ?g mL-1 microcystin-LR. Growth and peroxidase activity of C. fracta were not affected by microcystin-LR at concentrations up to 10 ?g mL-1. L. minor also accumulated microcystin-LR up to a concentration of 0.2880.009 ng mg-1 wet wt. plant material over the 5 days of the experiment, equivalent to an accumulation rate of 0.058 ng mg-1 day-1. C. fracta accumulated a microcystin-LR concentration of 0.0420.015 ng mg-1 wet wt. plant material over the 5 days of the experiment, equivalent to an accumulation rate of 0.008 ng mg-1 day-1. 2004 Elsevier Inc. All rights reserved.
Mitrovic, S.M., Hamilton, B., McKenzie, L., Furey, A. & James, K.J. 2005, 'Persistence of yessotoxin under light and dark conditions', Marine Environmental Research, vol. 60, no. 3, pp. 397-401.
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The change in concentration of the disulfated polyether yessotoxin (YTX) produced by a culture of the marine dinoflagellate Protoceratium reticulatum was measured in laboratory experiments under light and dark conditions. Experimental cultures were inoculated and grew at a growth rate of 0.14 d -1 until stationary phase was reached, after approximately 21 days. Cultures were maintained in the stationary phase until 31 days after inoculation. Cells of P. reticulatum contained a concentration of approximately 10-15 pg YTX cell-1 during stationary phase but this was considerably lower (<5 pg cell-1) during the growth phase. Low amounts of 45-hydroxy-YTX were also detected. At day 32, P. reticulatum was killed by cooling to 1C (confirmed microscopically) and YTX concentrations were measured periodically under light and dark conditions. YTX concentrations decreased rapidly to approximately 10% of the initial concentration within the first 3 days and depleted to near zero within a week in the light treatment. In the dark environment, YTX persisted longer with approximately 10% of the initial YTX concentration still remaining after 18 days. 2005 Elsevier Ltd. All rights reserved.
James, K.J., Gillman, M., Amandi, M.F., Lpez-Rivera, A., Puente, P.F., Lehane, M., Mitrovic, S. & Furey, A. 2005, 'Amnesic shellfish poisoning toxins in bivalve molluscs in Ireland', Toxicon, vol. 46, no. 8, pp. 852-858.
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In December 1999, domoic acid (DA) a potent neurotoxin, responsible for the syndrome Amnesic Shellfish Poisoning (ASP) was detected for the first time in shellfish harvested in Ireland. Two liquid chromatography (LC) methods were applied to quantify DA in shellfish after sample clean-up using solid-phase extraction (SPE) with strong anion exchange (SAX) cartridges. Toxin detection was achieved using photodiode array ultraviolet (LC-UV) and multiple tandem mass spectrometry (LC-MSn). DA was identified in four species of bivalve shellfish collected along the west and south coastal regions of the Republic of Ireland. The amount of DA that was present in three species was within EU guideline limits for sale of shellfish (20 ?g DA/g); mussels (Mytilus edulis), <1.0 ?g DA/g; oysters (Crassostrea edulis), <5.0 ?g DA/g and razor clams (Ensis siliqua), <0.3 ?g DA/g. However, king scallops (Pecten maximus) posed a significant human health hazard with levels up to 240 ?g DA/g total tissues. Most scallop samples (55%) contained DA at levels greater than the regulatory limit. The DA levels in the digestive glands of some samples of scallops were among the highest that have ever been recorded (2820 ?g DA/g). 2005 Elsevier Ltd. All rights reserved.
Mitrovic, S.M., Fernndez Amandi, M., McKenzie, L., Furey, A. & James, K.J. 2004, 'Effects of selenium, iron and cobalt addition to growth and yessotoxin production of the toxic marine dinoflagellate Protoceratium reticulatum in culture', Journal of Experimental Marine Biology and Ecology, vol. 313, no. 2, pp. 337-351.
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The marine dinoflagellate Protoceratium reticulatum has been recently identified as a source for the disulfated polyether toxin, yessotoxin (YTX), and may pose a risk to human health, aquaculture development and coastal environments. The requirements of P. reticulatum for selenium, iron and cobalt were assessed in culture. P. reticulatum was grown in nutrient enriched seawater (1/10 GP medium) without selenium or with 0.003 and 0.0003 ?M selenium added; without iron or with 0.076 and 0.0076 ?M iron added; and without cobalt or with 0.008 ?M cobalt added. Test flasks were monitored for growth rate, cell yield and YTX production. P. reticulatum was found to exhibit a strong requirement for both selenium and iron. Growth rate and cell yield in treatments without added selenium were significantly (P<0.05) reduced to 60.2% (?=0.15 day -1) and 20.2% (4942 cell ml -1), respectively, of those with selenium added (?=0.23 day -1 and 24, 387 cell ml -1). YTX production was significantly increased by addition of selenium in two of three transfers tested. Cells of P. reticulatum subjected to medium without selenium added showed morphological changes observable at the light microscope level which included enlarged cell size. The diameter of cells in medium without selenium added were significantly (P<0.05) enlarged to 36.70.90 ?m compared to cells in the medium with selenium added, 27.51.25 ?m. Growth rate and cell yield in treatments without added iron were also significantly reduced to 70.1% (?=0.16 day -1) and 34.2% (8003 cells ml -1), respectively, of those with iron added (?=0.23 day -1 and 23,416 cells ml -1). No significant effect on YTX production was measured. In contrast to selenium and iron, no limitation of growth or cell yield or differences in YTX production were o...
Mitrovic, S., Pflugmacher, S., James, K.J. & Furey, A. 2004, 'Anatoxin-a elicits an increase in peroxidase and glutathione S-transferase activity in aquatic plants', Aquatic Toxicology, vol. 68, no. 2, pp. 185-192.
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Although the toxic effects of cyanotoxins on animals have been examined extensively, little research has focused on their effects on macrophytes and macroalgae. To date only microcystins have been found to be detrimental to aquatic plants. Peroxidase activity of the free floating aquatic plant Lemna minor and the filamentous macroalga Chladophora fracta was measured after exposure to several concentrations of the cyanotoxin, anatoxin-a. Peroxidase activity (POD) was significantly (P<0.05) increased after 4 days of exposure to an anatoxin-a concentration of 25 g mL-1 for both L. minor and C. fracta. Peroxidase activity was not significantly increased at test concentrations of 15 g mL-1 or lower. In another experiment, the effects of various concentrations of anatoxin-a on the detoxication enzyme, glutathione S-transferase (GST) in L. minor were investigated. GST activity was significantly elevated at anatoxin-a concentrations of 5 and 20 g mL-1. Photosynthetic oxygen production by L. minor was also found to be reduced at these concentrations. This is the first report to our knowledge of the cyanotoxin anatoxin-a being harmful to aquatic plants.
Mitrovic, S.M., Oliver, R.L., Rees, C., Bowling, L.C. & Buckney, R.T. 2003, 'Critical flow velocities for the growth and dominance of Anabaena circinalis in some turbid freshwater rivers', Freshwater Biology, vol. 48, no. 1, pp. 164-174.
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From measurements at several weir pool sites along the turbid and freshwater Barwon-Darling River, Australia, the development of persistent stratification (for periods of >5 days) was related to river discharge. For the sites examined, the required discharge to allow the development of persistent stratification was between 100 and 450 ML day-1 during the hotter months. High discharge during the hotter months did not allow the formation of persistent stratification, although diel stratification did occur. Low discharge through the cooler months resulted in diel stratification, although persistent stratification lasting for a few days could occur at times. 2. The growth and dominance of Anabaena circinalis at these sites was closely related to the establishment and maintenance of persistent and strong thermal stratification. Growth only occurred during extended periods (>5 days) of persistent stratification. These conditions not only restrict the displacement of A. circinalis downstream, they also allowed the alga to accumulate in surface waters. 3. The discharge levels required to suppress the formation of persistent stratification at the study sites were variable because of large differences in channel cross-sectional area. To compensate for this variation, the discharges were converted to flow velocities. A critical velocity of 0.05 ms-1 was sufficient for the suppression of persistent thermal stratification and concurrent A. circinalis growth for all sites. The turbulent velocity (u*) under weak wind mixing at the study locations varied between 2.66 10-3 and 2.91 10-3 ms-1 at the critical flow velocities. These values may have potential to be applied to other rivers in similar climatic zones to suppress nuisance cyanobacterial growth.
Mitrovic, S.M., Howden, C.G., Bowling, L.C. & Buckney, R.T. 2003, 'Unusual allometry between in situ growth of freshwater phytoplankton under static and fluctuating light environments: Possible implications for dominance', Journal of Plankton Research, vol. 25, no. 5, pp. 517-526.
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The effects of fluctuating light fields on the growth of phytoplankton are not well understood and conclusions in the literature have been equivocal. Most studies have examined responses such as productivity and chlorophyll a content (laboratory culture and field tests) or growth rates (laboratory' culture tests). In this study we examined the in situ growth rates of different types of phytoplankton within two natural populations. Comparisons were made between populations grown in a static environment (suspended in a fixed position in the water column) and an equivalent population moving through the water column simulating the mixing of entrained phytoplankton. Growth under fluctuating light fields in this experiment only significantly (P < 0.05) increased the growth of the diatom Skeletonema and decreased the growth of Anabaena circinalis, Microcystis aeruginosa and Scenedesmus sp. All other phytoplankton, including the genera Nitzschia, Fragilaria and Dactylococcopsis, did not have growth rates that were significantly different between static and fluctuating light treatments. A general pattern where diatoms grew best, followed by chlorophytes with the toxicogenic cyanophytes M. aeruginosa and A. circinalis growing least well, was distinguished under fluctuating irradiance. This seems consistent with the common occurrence of these groups of phytoplankton in the natural environment. The cyanophytes Dactylococcopsis and Aphanothece did not follow this pattern, with the former growing better under fluctuating light and the latter exhibiting an unusual growth pattern where growth was higher under lower light intensities.
Mitrovic, S., Bowling, L.C. & Buckney, R.T. 2001, 'Responses of phytoplankton to in-situ nutrient enrichment: Potential Influences on Species Dominance in a River', International Review of Hydrobiology, vol. 86, no. 3, pp. 283-296.
The Hawkesbury River at Sackville, New South Wales, Australia is fresh and vigorously mixed by tidal movement. The location has frequent blooms of Microcystis aeruginosa, which have been recorded occurring throughout the year, including winter temperatures as low as 13 C. Nutrient enrichment tests were performed in-situ on the natural phytoplankton population in 1997 and 1998 while Microcystis aeruginosa dominated (covering both summer and winter periods). These experiments compared population changes under the ambient nutrient regime with those after additions of ortho-phosphate, nitrate, ammonia and various combinations of these nutrients. Under ambient conditions, the Microcystis population was able to grow significantly (P < 0.05) while most non-cyanobacterial phytoplankton did not. Nutrient additions induced a variety of nutrient limitation responses that often varied between genera of major groups i.e. in the Chlorophyceae (Actinastrum sp. responded to phosphorus while Psephonema sp. responded to nitrogen). The possibility that shifts in population dominance from Chlorophyceae to the Cyanobacteria (M. aeruginosa) at Sackville are in response to competition for limiting nutrients is discussed
Mitrovic, S.M., Bowling, L.C. & Buckney, R.T. 2001, 'Quantifying potential benefits to Microcystic aeruginosa through disentrainment by buoyancy within an embayment of a freshwater river', Journal of Freshwater Ecology, vol. 16, no. 2, pp. 151-157.
Vertical profiles of Microcystis aeruginosa and other phytoplankton were measured on several occasions within the main channel and an embayment of a freshwater tidal river. The cyanobacteria M. aeruginosa and Anabaena circinalis were able to migrate to surface waters within the embayment but not within the main channel. Using a quantitative estimate of primary productivity (over a 24 hour period), the potential benefits through disentrainment by buoyancy were determined for M. aeruginosa within the embayment and compared to the main channel. The population within the embayment had a daily integral of photosynthesis of 603.13 mmol of O2m-2, nine times greater than the evenly distributed main channel population with a daily integral of 62.08 mmol of O2m-2. It is likely that embayments along the tidally mixed reaches of the Hawkesbury River may be areas where M. aeruginosa can disentrain through buoyancy and enhance primary productivity rates.
Mitrovic, S.M., Bowling, L.C. & Buckney, R.T. 2001, 'Vertical disentrainment of Anabaena circinalis in the turbid, freshwater Darling River, Australia: Quantifying potential benefits from buoyancy', Journal of Plankton Research, vol. 23, no. 1, pp. 47-55.
The migration patterns of phytoplankton through time and depth were measured in the Darling River at Trevallyn, New South Wales, Australia during a bloom of Anabaena circinalis. Anabaena circinalis was able to disentrain and maintain position within surface waters during the early morning, coinciding with the diel period of least wind speeds and a state of no detectable thermocline (0.1C detection limit). Anabaena circinalis concentrations were up to 10 times higher in the surface waters than in the bottom waters during the morning sampling periods. Afternoon and midnight sampling periods revealed either a small amount of surface accumulation or none. All other phytoplankton were found to have a relatively even distribution throughout the water column at all time periods measured (except Aulacoseira on one occasion). These vertical distribution data were used to determine the potential benefit buoyant A.circinalis could gain over an evenly distributed population using a quantitative estimate of primary productivity. The buoyant population was found to have a daily integral of photosynthetic O2 production of 3.63 mol m-2 five times greater than that for the evenly distributed population. Losses due to respiration were greater for the evenly distributed population (29.5%) than the buoyant population (4.8%), probably due to the amount of time cells spent outside the euphotic zone. It is suggested that buoyancy may offer considerable advantage to A.circinalis in gaining dominance in turbid freshwater rivers. Further, buoyancy may offer some advantage even without strong thermal gradients.