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Basin Theme: Food webs & water quality

Food webs show how food and energy resources such as microbes, algae and reeds are connected with consumers such as waterbugs, fish and waterbirds. Water quality and stream metabolism provide the oxygen and environment for aquatic plants and animals to thrive, and both respond to flow management to provide the energy that fuels riverine food webs. Our work will investigate how Commonwealth environmental water impacts food webs and water quality in the rivers, floodplains and wetlands of the Murray-Darling Basin.

Murray River system near Albury, NSW.  Photo credit: Paul McInerney

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Why focus on food webs & water quality?

Water for the environment is often used to support native fish recruitment and successful waterbird breeding. But how many fish and waterbirds can be sustained by a flow event? And for how long? To answer these questions we need to understand how water for the environment can provide the water quality and food resources of the right quality in the right amounts for these native organisms to thrive.

Our aim is to understand, and be able to predict how Commonwealth environmental water influences water quality (nutrients, temperature, light, and salinity), which in turn can regulate rates of metabolism and productivity (energy availability).  We will explore how this energy fuels the carrying capacity (how many waterbugs, fish and birds) of food webs that support fish and waterbird recruitment.

Energy is a fundamental requirement for all organisms. Without energy, organisms have no capacity for growth or reproduction. Food webs describe the pathways along which energy is transferred from resource to consumer, and the strength and direction of these pathways are sensitive to impacts from changes to river flows and their landscapes. Although complex, food web studies can identify critical parts of an ecosystem that influence energy production and transfer and which, in turn, influence how many iconic native fish and waterbirds can be supported.

Just like humans, the diet of aquatic animals is as much about the quality of food, as the quantity. Quality food resources for aquatic animals is mostly about nutrition. For healthy growth, function, and reproduction, we need to understand how water for the environment can be delivered to provide native animals with the essential micro and macronutrients they need, as well as sufficient energy.

Our work will inform the efficient and strategic use of water for the environment to deliver water quality and food webs to support thriving and sustainable communities of plants, native fish and waterbirds.

Interplay of food web and flow models. Source: EWKR Power Supply (full story below)

Our approach

Our activities aim to establish links between water quality and environmental water delivery. Understanding these links will enable us to then make the connection between environmental water and energy production. We are focusing on in-stream channel environments in each of the seven Selected Areas. Data from Selected Areas will provide us with information about how water quality factors such as nutrients, temperature and light may differ across parts of the Basin.

The evaluation component of this Theme will build on the activities of the Long Term Intervention and Monitoring (LTIM) project to describe the response of ecosystem energetics to Commonwealth environmental water in both the short (<1year) and longer (1-7 years) term. We will broaden the data currently available, and develop new approaches to deliver a Basin scale assessment of the influence of Commonwealth environmental water on water quality and energy production. In addition, we aim to design river scale energetics models by directly linking evaluation outcomes with food web energetics research.

This research will aim to address:

Our research will focus on developing an energetics response model which will enable us to predict the trophic (food and nutrition) carrying capacity of rivers and wetlands in response to environmental water delivery.  The primary question this project aims to address is what did Commonwealth environmental water contribute to the production of energy, quality of food resources, and transfer into river channel and floodplain wetland food webs to support native fish and water bird recruitment?

This research program is designed to fill gaps identified in the development of the Environmental Water Knowledge and Research (EWKR) project food webs model and improve the certainty of our predictions for ecological outcome.   We will organise our research in the following areas:

  • Building channel and wetland scale food web structures – this will involve a review of existing data, molecular ecology and environmental-DNA of trophic resources and food webs dynamics in wetlands, flood channels and rivers.
  • Investigating trophic transfer efficiencies: energetic requirements of key biota.
  • Analysing in-situ response of basal resources (microbes/fungi, algae, cyanobacteria, diatoms, biofilm, dissolved organic carbon, macrophytes) and their quality (fatty acids as food ‘quality’ biomarkers) to food webs to watering.
  • Developing energy budgets (from Metabolism indicator) at reach, catchment and basin scales.

Current activities

We are undertaking a mix of evaluation and research activities:

Evaluation

We will undertake a review of the Standard Methods and Foundation Reports for Water Quality and Metabolism in consultation with Selected Area Theme Leaders. From this we will develop a new ‘value statement’ and message for the Theme that identifies the intrinsic value of food webs and demonstrates clear links to other Themes. For example, food webs means many things to many people; our communication of water quality, metabolism and food webs within and outside Flow-MER will be most effective with clear statements of our meaning and scope.

We will scope the availability of water quality and dissolved oxygen data from our State Agency collaborators so that we extract, collate and include this information in Flow-MER Basin scale Evaluation reports. Our evaluation efforts will also seek to develop modelling and scaling tool(s) to support Basin scale evaluation.

Image: Adding water to floodplains releases nutrients that build the food webs to support the boom in aquatic life. Photo credit: Darren Ryder

Research: Building channel and wetland scale food web structures

This work will involve reviewing existing data, molecular ecology and environmental-DNA analyses of trophic resources and food web dynamics in wetlands, flood channels and rivers. There will be close links with research being undertaken in the Biodiversity Theme’s Refugia research project, and fieldwork will be carried out at Selected Area sites in the Gwydir, Darling and Lachlan Rivers.

To assess the health of zooplankton and fish and the nutritional quality of their diets we will use stable isotope analyses and interrogate fatty acid dynamics in zooplankton, juvenile fish and their food items, to compare how patterns differ between floodplain wetlands, flood channel/refuges and the river channel. This work will improve our understanding of how environmental water can be used to promote the transfer of important molecules through food webs is a key next step from the work carried out in EWKR.

Image: With a big enough food supply the floodplains of the Murray-Darling Basin become a soup of highly productive invertebrates as seen by the mass of shrimp from the Warrego floodplain. Photo credit: Gavin Butler

Research: Measuring the energetic requirements of key biota

Small scale laboratory experiments will be undertaken to determine growth rates and ingestion/clearance rates for zooplankton and juvenile fish. Rates determined from these experiments are critical to the development of the energetics model.

Image: Wetlands are important breeding grounds for waterbirds and fish, but how do we know how much water is needed to optimise breeding outcomes? Photo credit: Daryl Albertson

Research: Response of basal resources and their quality to food webs

We are observing in-situ responses of basal resources (microbes/fungi, algae, cyanobacteria, diatoms, biofilm, DOC, macrophytes) and their quality (Fatty acids as food ‘quality’ biomarkers) to food webs to watering. Work carried out by the EWKR food web theme showed that floodplain habitats could provide higher quality basal food resources for fish larvae than the river channel. Knowledge gaps remain, however, in our understanding of how managed flows can be manipulated to maximise these food resources.

Image: Exploring river and wetland food webs is often best done in mesocosms where we can control environmental factors such as temperature, depth and food sources. Photo credit: Ivor Growns

Research: Food web model

By incorporating data generated from the above activities, we will develop a bioenergetic food web model using Ecopath with Ecosim software. The model will be used to demonstrate rates of carbon transfer and production in the food web under different environmental flow scenarios to illustrate the changes in productivity (phytoplankton and zooplankton) and fish outcomes.

Image: Monitoring at reach scale will provide input data for new models. Photo credit: Darren Ryder

Reed beds in a Millewa Forest wetland.
Photo credit: Heather McGinness

Our team

Dr Paul McInerney

Paul’s research focus areas include food webs, how energy flow in ecosystems may be changed by both biotic and abiotic disturbance, or by man-made intervention, and how invasive species alter the structure and function within freshwater ecosystems. He is also interested in the responses of basal resources to altered ecosystem conditions, and how this influences food webs.

Professor Darren Ryder

Darren is a Professor in aquatic ecology and Leader of the Aquatic Ecology and Restoration Research Centre at the University of New England. He has over 18 years’ experience in research in aquatic ecosystems in coastal and inland rivers and wetlands of eastern Australia. His research expertise has a focus on the effective management and restoration of freshwater ecosystems.

Gavin Rees

Gavin trained as a microbiologist and has worked on projects as diverse as waste water treatment and using microbes to clean up hydrocarbon-contaminated soils.  He focuses on understanding the many roles microbes play in rivers and wetlands including how organisms respond to a variety of environmental conditions, whether natural or man-made, and the consequences of those responses.

Dr Joanne Bennett

Joanne is a community and spatial ecologist. Her primary research goal is to discover the general principles that are essential to effectively manage biodiversity under global changes particularly land-use and climate change. She has worked on a wide range of taxa including mammals, reptiles, invertebrates, birds and vegetation in a wide of ecosystems.

James Hitchcock

James is an aquatic ecologist and post-doctoral research fellow at the University of Canberra. His research focuses on food webs, water quality, and ecosystem productivity. He is interested in understanding how human activity is disrupting aquatic food webs and assessing potential management interventions.

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