Improving The Efficient Use of Environmental Flows
National Environmental Research Program (NERP) - Improving the efficient use of environmental flows
The connection of rivers to their floodplain allows for dispersal of organisms, as well as promoting biogeochemical processes on the floodplain. As a consequence, flood return waters may contain large amounts of organic material and nutrients. Much of the dissolved carbon is biodegradable (albeit different types of carbon are degraded over different time frames), and can lead to increased activity and biomass of microbial and algal communities, which in turn can potentially fuel food webs. The project contained four major components, each designed to examine the benefits and disbenefits of environmental watering:
The Commonwealth Government is investing a large amount of money and resources in securing and delivering water to protect and restore the condition of water-dependent ecosystems, particularly in lowland rivers within the Murray-Darling Basin (MDB). The purpose of the project described here is to improve our understanding of how this water can be used to benefit the ecology of lowland river systems while minimizing disbenefits.
A series of models exist in the scientific literature that describe how the biological components of rivers respond to physical and environmental conditions. The key to each these models is understanding the sources of carbon and energy that drive the food webs in rivers, and determining whether carbon and energy generated within a river through algal production or carbon returned through floodplain inundation is important in fueling food webs. Specific details of models seek to describe how these change along the length of rivers (including the role of weir pools and reservoirs) and how changes may occur when rivers and floodplains become connected.
Current understanding of the function of rivers of the lower MDB suggests that in-stream processes are the major source of carbon and energy for food webs. However, many of these studies were carried out during periods of low flows in the MDB, (e.g. during the millennium drought), so contributions of flooding were not always included in such studies. Similarly, such work has not always been carried out over very long time frames, so floods have not generally been captured as part of monitoring programs.
Connectivity between the river and its floodplain not only alters foodwebs, but also extends the habitat over which native fish can move. There have been a number of monitoring programs throughout the MDB that have examined fish movement, but few have extended over multiple years and good understanding of the annual variability in fish movement is lacking.
The effectiveness of environmental flows depends on the response of ecosystem functions such as hydrological connectivity, as acknowledged in the Murray-Darling Basin Plan (Basin plan). Lateral hydrological connectivity is important due to the exchange of material, including nutrients and organic matter, and dispersal of animals and plants. Knowledge of the outcomes of lateral connectivity is developing, but considerable uncertainty remains. It is important to reduce this uncertainty so that risks can be minimised and trade-offs dealt with explicitly.
This project examined several aspects of lateral connectivity, including the exchange of organic matter and fish dispersal and showed some clear benefits of blackwater to the aquatic ecosystems. Some biota responded in a positive way to the blackwater, others were temporarily affected, whereas some biota (plants) showed no response either way. In summary findings include:
1. Riverine biofilms and macroinvertebrates showed a range of positive responses to waters rich in carbon and nutrients.
2. Aquatic plant communities showed different responses, depending on species and the state of growth.
3. In contrast to aquatic plants, hypoxic blackwater conditions had significant negative affects on microinvertebrate emergence from sediments.
4. Connectivity also provided an opportunity for young catfish to move out of the wetland.
View clips of Dr Daryl Nielsen and Rob Cook from MDFRC presenting some of the findings of this project at the Barmah-Millewah conference hosted by the Goulburne Broken CMA in 2013 (on our YouTube tab).
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