Aquatic Ecosystem Function task

Using isotopes to evaluate how freshwater ecosystems function.

Water is a vital resource that is under ever-increasing demand from population and industry growth, agricultural development and environmental allocations that are crucial in sustaining the natural ecosystems upon which we all rely.

Aquatic ecosystems, including rivers and wetlands, are complex systems with numerous dynamic relationships between water, earth, air, plants and animals.

Nuclear techniques provide unique benefits in the study of freshwater ecosystems, and are utilised by ANSTO's Aquatic Ecosytem group to better understand their complex nature and inform decisions for water use.

A key tool utilised at ANSTO is the measurement of the natural abundance of stable isotope ratios (ratio of heavy to light stable isotopes for any element) to determine food web structures, to track changes in ecosystems over time, and to understand the cycling of nutrients and pollutants through aquatic ecosystems.

The ratios of isotopes may vary or change in nature due to physical, chemical and biological processes. This is known as isotope fractionation, and it is based on the fact that heavy isotopes do not respond as quickly to change as light ones do.

Important applications include tracking how these isotope ratios (and thus the ecosystem) change as a result of drought, climate change, human impacts and other events. The research can provide valuable insights as decisions are made about the use and protection of Australia's waterways.

Examples of isotope applications in aquatic ecosystems:

The isotopic composition of living creatures is a reflection of what they eat. The level of nitrogen enrichment tells the researchers where specific organisms sit in the food web, while the carbon isotopes show what plants or prey the organism is consuming, and in what proportion.

Environmental variations in the stable isotope ratios of carbon and nitrogen over time for any organism will reflect diet shifts in response to, for example, water availability changes or the availability of new nutrient sources that may be the result of altered management practices. The same isotopes can help the researchers see changes in age and size ranges in populations because fractionation is age dependent. They can also identify where animals have come from, such as from wild versus aquaculture production.

Stable isotope ratios can also reveal how much transpiration, compared with evaporation is occurring in wetland vegetation, how much floodwater infiltrates the soil, and from which depths in the soil the wetland plants are obtaining their water. This information is important when water for the environment is scarce, and decisions must be made about how much water needs to be allocated to sustain our vital wetlands.

Radioecology

ANSTO uses specialised equipment that can detect a wide range of isotopes, including natural or man-made radioisotopes. Radioactive isotopes have a number of different advantages compared to stable isotopes for biological studies.

One of the main benefits is that they decay with a specific half-life. This factor can tell the researchers how quickly things happen in the environment, particularly in response to disturbance. These kinds of isotopes can be tracked as plants take up minerals and nutrients from soil and water and as animals eat plants. By tracking the course of these tracers, much is revealed about how plants and animals function, and relate to one another.

Radioisotopes are also particularly helpful in studies on the nature of pollution. For example, how heavy metals such as copper, zinc and lead move through aquatic systems and how they bioaccumulate. Many of Australia's wetlands and sediments already contain these metals and ANSTO's studies can help establish under what conditions they will remain in place or become mobile.

Research areas and collaborations

Current research locations include the Macquarie Marshes in central-west NSW, the Gwydir wetlands in north-west NSW, and Yanga, located on the Lower Murrumbidgee River floodplain in south-western NSW. Each of these wetlands has international recognition with listing as Ramsar sites.

This means Australia has an obligation to ensure that their ecological character is maintained over time, and ANSTO's studies are directly related to the success of this treaty. Key aspects of this research are performed in collaboration with the NSW Department of Environment and Climate Change, the University of Canberra, the Australian Catholic University and the University of New England, among others.

Key instruments

Isotope Ratio Mass Spectrometry (IRMS) is used to measure stable isotope ratios in the ecological samples collected by the team. Mass spectrometry relies on differences between the mass of stable isotopes to separate them during the analysis process.

Radioisotopes are measured on a range of instruments at ANSTO, depending on the type of isotope and level of precision needed. ANSTO has a range of gamma ray spectrometers, some with extremely low levels of detection. Also available within ANSTO's Institute for Environmental Research are Accelerator Mass Spectrometry (AMS) and Ion Beam Analysis (IBA) capabilities which present detailed isotopic and materials analysis.

Other functions and research areas

The Aquatic Ecosystem team supports additional research related to the dynamic nature of isotope response to environmental change, species and habitat response to climate change, and impacts of contaminants on aquatic environments. This work helps the researchers better interpret field observations.

The team has a range of laboratory capabilities including a controlled aquarium room used for studying plants, arthropods and fish. Current research includes raising a group of yabbies to determine effects of food selection differences that often occur in the real world as a consequence of seasonal changes, or following events such as floods.

Other laboratories include controlled study areas for radiotracers that provide researchers with insights into how wetlands typically accumulate and release nutrients and contaminants.

Publications

A list of current publications can be found here:

Team members and contacts

Debashish Mazumder Stable Isotope Ecology
Institute for Environmental Research
Australian Nuclear Science & Technology Organisation (ANSTO)
Locked Bag 2001 Kirrawee DC  NSW 2232
T: +61 2 9717 9219
F: +61 2 9717 9260
E:  debashish.mazumder@ansto.gov.au

Dr Mat Johansen, Radioecology
Institute for Environmental Research
Australian Nuclear Science & Technology Organisation
Locked Bag 2001 Kirrawee DC  NSW 2232

T: +61 2 9717 3060
F: +61 2 9717 9260
E: Mathew.johansen@ansto.gov.au
Dr Suzanne Hollins, Isotope Hydrology/Ecohydrology
Institute for Environmental Research
Australian Nuclear Science & Technology Organisation (ANSTO)
Locked Bag 2001 Kirrawee DC NSW 2232
T: +61 2 9717 3701
F: +61 2 9717 9260
E:  Suzanne.hollins@ansto.gov.au