I’m an aquatic ecologist in the Freshwater and Estuarine Research Group. My work focuses on the management and restoration of aquatic ecosystems. I'm particularly interested in understanding how food webs are impacted by anthropogenic activities. My current research addresses how miroplastics, eutrophication, and altered flow regimes influences zooplankton and trophic dynamics. I’ve previously worked for the state government implementing water quality and ecological aspects of the Basin Plan. I have a growing interest in the role of ecology in broader interdisciplinary approaches to environmental problems.
Professional soceity memberships:
- Australian Freshwater Sciences Society (AFSS)
- Association of Scientists in Limnology and Oceanography (ASLO)
- Aquatic foodwebs
- Plankton ecology
- Carbon biogeochemistry
- Environmental flows
- Aquatic Ecology 91121
- Stream and Lake Assessment 91155
© 2020 Microplastic (MP) pollution is an emerging issue in aquatic sciences. Rain and storm events are responsible for the mobilization and transport of a range of pollutants in aquatic systems, yet to date no study has examined how microplastic abundance changes in waterways during such events. The aim of this study was to determine how microplastic concentrations changed over the course of the storm event in an urban estuary. Sampling was conducted at high frequency before, during, and after a storm event that caused flooding in the Cooks River estuary, Australia. Microplastic abundance increased during two days of heavy rain from 400 particles m3 before storm event to up to 17,383 particles m3 after the event. Variation in microplastic abundance was positively related to five-day average antecedent rainfall. The results highlight the importance of rain and storm events as key moments of microplastic contamination in aquatic systems. The results have implications for considering the maximum number of microplastics that aquatic life may be exposed to and the importance of strategies to manage stormwater to minimize the input of microplastics to aquatic ecosystems.
Michie, LE, Hitchcock, JN, Thiem, JD, Boys, CA & Mitrovic, SM 2020, 'The effect of varied dam release mechanisms and storage volume on downstream river thermal regimes', LIMNOLOGICA, vol. 81.View/Download from: Publisher's site
Pearse, R, Hitchcock, JN & Keane, H 2019, 'Gender, inter/disciplinarity and marginality in the social sciences and humanities: A comparison of six disciplines', Women's Studies International Forum, vol. 72, pp. 109-126.View/Download from: Publisher's site
Gray, R, Jones, HA, Hitchcock, JN, Hardwick, L, Pepper, D, Lugg, A, Seymour, JR & Mitrovic, SM 2019, 'Mitigation of cold-water thermal pollution downstream of a large dam with the use of a novel thermal curtain', River Research and Applications, vol. 35, pp. 855-866.View/Download from: Publisher's site
© 2019 John Wiley & Sons, Ltd. Hypolimnial releases from dams during periods of thermal stratification modify the downstream riverine thermal regime by decreasing water temperature and reducing natural diel thermal variability. This cold-water thermal pollution in rivers can persist for hundreds of kilometres downstream of dams and impact important ecological processes such as fish spawning. To mitigate this problem, a first-of-its-kind thermal curtain was fitted to the large bottom release Burrendong Dam on the Macquarie River, Australia. The thermal curtain acts by directing warmer, near-surface epilimnial water to the low-level hypolimnial offtake. This study aimed to test the efficacy of the thermal curtain by measuring temperatures before and after the curtains installation, quantifying the magnitude and extent of cold-water thermal pollution along the Macquarie River downstream of Burrendong Dam. Epilimnial releases with use of the curtain increased diel temperature ranges and the mean monthly water temperature below the dam. Epilimnial releases with use of the curtain increased diel temperature ranges from 0.9°C to 2.5°C and reduced the difference between the mean monthly water temperature of an upstream control and a downstream site by up to 3.5°C. A comparison of the monthly temperature means along the river, indicated that thermal recovery, whereby temperatures returned to within the natural range of upstream temperatures occurred 45 km downstream of the dam during summer when the thermal curtain was deployed, compared with approximately 200 km prior to deployment of the curtain. Our study suggests that the use of thermal curtains can reduce cold-water thermal pollution and improve ecological outcomes for river ecosystems downstream of dams.
Hitchcock, JN & Mitrovic, SM 2019, 'Microplastic pollution in estuaries across a gradient of human impact.', Environmental pollution (Barking, Essex : 1987), vol. 247, pp. 457-466.View/Download from: Publisher's site
Microplastic (MP) pollution is an emerging issue in aquatic sciences. Little comparative information currently exists about the problem in coastal systems exposed to different levels of human impact. Here we report a year-long study on the abundance of MP in the water column of three estuaries on the east-coast of Australia. The estuaries are subject to different scales of human impact; the Clyde estuary has little human modification, the Bega estuary has a small township and single wastewater treatment works discharging to its waters, and the Hunter estuary which has multiple townships, multiple wastewater treatment plants, and heavy industry. MP abundance followed an expected pattern with the lowest abundance in the low-impact Clyde estuary (98 part. m3), moderate levels of MP in the moderately impacted Bega estuary (246 part. m3), and high MP abundance in the highly impacted Hunter estuary (1032 part. m3). The majority of particles were <200 μm and fragment-like rather than fiber-like. MP abundance was positively related to maximum antecedent rainfall in the Bega estuary, however there are no clear environmental factors that could explain MP variation in the other systems. MP were generally higher in summer and following freshwater inflow events. On the Hunter estuary MP abundance was at times as high as zooplankton abundance, and within the range of numbers reported in other highly impacted systems globally. The results confirm that higher levels of human impact lead to greater plastic pollution and highlight the need to examine aquatic ecosystems under a range of conditions in order to adequately characterize the extent of MP pollution in rivers and coastal systems.
Hitchcock, JN, Mitrovic, SM, Hadwen, WL, Growns, IO & Rohlfs, A-M 2016, 'Zooplankton responses to freshwater inflows and organic-matter pulses in a wave-dominated estuary', MARINE AND FRESHWATER RESEARCH, vol. 67, no. 9, pp. 1374-1386.View/Download from: Publisher's site
Hitchcock, JN, Mitrovic, SM, Hadwen, WL, Roelke, DL, Growns, IO & Rohlfs, AM 2016, 'Terrestrial dissolved organic carbon subsidizes estuarine zooplankton: An in situ mesocosm study', Limnology and Oceanography, vol. 61, no. 1, pp. 254-267.View/Download from: Publisher's site
© 2016 Association for the Sciences of Limnology and Oceanography. Freshwater inflows play an important role in delivering dissolved organic carbon (DOC) to estuaries. Episodic inputs of DOC may support increased bacterial production. However, the role of DOC in supporting zooplankton production is widely deb ated. To evaluate this role we performed an in situ mesocosm experiment in the Bega River estuary, Australia. We added a DOC leachate derived from terrestrial vegetation to 400 L mesocosm bags as treatments of +1.5, +3, and +16 mg C L -1 and monitored changes in carbon, nitrogen, phosphorus, bacteria, chlorophyll a (Chl a), and zooplankton over 22 d. Bacterial biomass peaked at day 2 and was highest in the +16 mg C L -1 treatment. Chl a was not significantly different between treatments. Mesozooplankton was dominated by copepodites of Gladioferens pectinatus and Sulcanus conflictus between days 5-9 and by adults between days 9-15. Significantly higher numbers of copepods were present in the +16 treatment followed by the +3 mg C L -1 treatment compared with the controls. Stable carbon isotope signatures of copepods in the +16 mg C L -1 treatment were significantly different from the control and showed leachate carbon supported between 29.3% and 55.8% of copepod biomass. These results suggest that the impact of allochthonous DOC loading events on estuarine zooplankton occurs over short periods, and that the magnitude of response is, in part, controlled by the quantity of bioavailable DOC loaded to the system. Our findings underscore the importance of microbial dynamics stimulated by DOC loading events from freshwater inflows as a trophic path in estuarine food webs.
Rohlfs, A-M, Mitrovic, SM, Williams, S, Hitchcock, JN & Rees, GN 2016, 'Dissolved organic carbon delivery from managed flow releases in a montane snowmelt river', AQUATIC SCIENCES, vol. 78, no. 4, pp. 793-807.View/Download from: Publisher's site
Hitchcock, JN & Mitrovic, SM 2015, 'After the flood: changing dissolved organic carbon bioavailability and bacterial growth following inflows to estuaries', BIOGEOCHEMISTRY, vol. 124, no. 1-3, pp. 219-233.View/Download from: Publisher's site
Hitchcock, JN & Mitrovic, SM 2015, '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, vol. 156, pp. 71-82.View/Download from: Publisher's site
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...
Mitrovic, SM, Westhorpe, DP, Kobayashi, T, Baldwin, DS, Ryan, D & Hitchcock, JN 2014, 'Short-term changes in zooplankton density and community structure in response to different sources of dissolved organic carbon in an unconstrained lowland river: evidence for food web support', Journal of Plankton Research, vol. 36, no. 6, pp. 1488-1500.View/Download from: Publisher's site
Hitchcock, JN & Mitrovic, S 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, no. 1, pp. 106-115.View/Download from: Publisher's site
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 1.25 L 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.
Hitchcock, JN, Mitrovic, S, Kobayashi, T & Westhorpe, DP 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.View/Download from: Publisher's site
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 mic
Mitrovic, S, Hitchcock, JN, Davie, AW & Ryan, D 2010, 'Growth Responses Of Cyclotella Meneghiniana (Bacillariophyceae) To Various Temperatures', Journal Of Plankton Research, vol. 32, no. 8, pp. 1217-1221.View/Download from: Publisher's site
The growth of Cyclotella meneghiniana was examined at temperatures between 13 and 28°C at 3°C intervals. Growth increased linearly with temperature to a growth maximum at 25°C, with growth decreasing at 28°C.
- Department of Primary Industries
- Hunter Water
- Water NSW
- Snowy Valleys Council