Land use on the Murrumbidgee River

Full Title

Determining the impact of land use on wetlands through an examination of organic matter dynamics and secondary production in floodplain wetlands of the lower Murrumbidgee River

Contact Person 

Suzanne Watkins

Project Team

Daryl Nielsen, Ben Gawne

Funding Body

Department of Environment and Climate Change

Duration

March 2008 - May 2009

Outcomes 

This project will contribute to our understanding of organic matter dynamics within floodplain wetlands, and allow wetlands of the lower Murrumbidgee floodplain to be managed to maximise secondary productivity and biodiversity, and maximise food resources for higher consumers such as birds and fish.

Summary

The transfer of organic carbon and flow of nutrients in aquatic systems largely determines the structure of food webs and the abundance and biodiversity of biota. Changes to the amount and type of organic matter entering aquatic systems can alter biogeochemical processes, water quality and primary production (Robertson et al., 1999), which in turn impacts secondary producers, potentially altering the food web (Bunn, 1986).

Floodplain wetlands support a great diversity of flora and fauna and are significant habitats and areas of productivity in floodplain systems (Hillman, 1986), however, little is known about the effects of changing the management of the landscape in which wetlands are imbedded. One potentially significant impact of changed land use is alterations to organic matter and nutrient input. Allochthonous organic matter inputs into wetlands can be significant (Briggs & Maher, 1983), characteristically accumulating in large quantities in some systems (Glazebrook & Robertson, 1999).

A large proportion of the Murray-Darling Basin floodplain has been highly developed since European settlement, and is predominantly used for grazing and cropping. As a consequence, large-scale clearing of floodplain forest has occurred (Dexter, 1978), and the water requirements of irrigated agriculture have altered flow and floodplain inundation regimes (Walker & Thoms, 1993). These changes to land use have resulted in increased erosion, algal blooms and changes in aquatic macrophyte communities in wetlands (Robertson, 1997; Crosslé & Brock, 2002) and are usually coupled with clearing and the loss of riparian vegetation, which further compounds these impacts since riparian vegetation acts to buffer aquatic systems from the effects of the surrounding landscape (Naiman & Decamps, 1997). Consequently, modification to floodplain land use can greatly alter organic matter quality and quantity and nutrient cycling within wetlands (Robertson, 1997) which in turn impacts on aquatic biota that depend on organic matter as a food resource and habitat. Clearing riparian vegetation has been shown to alter invertebrate community structure (Delong & Brusven, 1998), potentially as a consequence of a reduction in organic matter input.

This project proposes to determine the organic matter dynamics of wetlands on floodplains of differing land uses, and the community structure of primary consumers which rely on these resources. The major land use types within the lower Murrumbidgee River floodplain will be identified, and wetlands within these land use types will be selected along with reference sites in relatively undisturbed areas. These wetlands will be assessed to determine the differences in the quality (C:N:P ratio) and quantity of organic matter and nutrients available to the aquatic food web, and the community structure of primary consumers. Links between the diversity of these biota and organic matter dynamics will enable us to develop a model of energy transfer in these systems according to land use type.

This project will generate knowledge that will facilitate the management of floodplains to optimise environmental outcomes for wetlands. Improved knowledge of the impacts of changed land use on wetlands will enable greater prioritisation of rehabilitation actions to maximise the environmental outcomes within limited budgets.

Objectives:

The aim of this project will be to determine the organic matter dynamics of floodplain wetlands within areas of differing land use, and the impact of this on primary consumers. Specifically, the project will achieve the following:

1. Determine the major land use types within the lower Murrumbidgee floodplain.
2. Determine the quality (C:N:P ratio), quantity and source of organic matter within wetlands of varying floodplain land use types.
3. Quantify the abundance and richness of primary consumers within floodplain wetlands.
4. Recommend management strategies for maximising the biodiversity of secondary producers.

Site selection:

Sites will be selected in the lower Murrumbidgee floodplain following an initial assessment of major land use types. Wetlands in several land use categories will be selected and surveyed seasonally over approximately 6 months (summer/spring). 

References:

Briggs, S.V. & Maher, M.T. (1983) Litter fall and leaf decomposition in a river red gum (Eucalyptus camaldulensis) swamp. Australian Journal of Botany, 31, 308-316.

Bunn, S.E. (1986) Origin and fate of organic matter in Australian upland streams. In: Limnology in Australia (eds P. De Deckker & W.D. Williams). CSIRO, Melbourne.

Crosslé, Katharine & Brock, Margaret A. (2002) How do water regime and clipping influence wetland plant establishment from seed banks and subsequent reproduction? Aquatic Botany, 74, 43-56.

Delong, M. D. & Brusven, M. A. (1998) Macroinvertebrate community structure along the longitudinal gradient of an agriculturally impacted stream. Environmental Management, 22(3), 445-457.

Dexter, B.D. (1978) Silviculture of the river red gum forests of the central Murray floodplain. Proceedings of the Royal Society of Victoria, 90, 175-191.

Glazebrook, H.S. & Robertson, A.I. (1999) The effect of flooding and flood timing on leaf litter breakdown rates and nutrient dynamics in a river red gum (Eucalyptus camaldulensis) forest. Australian Journal of Ecology, 24, 625-635.

Hillman, T.J. (1986) Billabongs. In: Limnology in Australia (eds P. De Deckker & W.D. Williams). CSIRO, Melbourne.

Naiman, R.J. & Decamps, H. (1997) The Ecology of Interfaces: Riparian Zones. Annual Review of Ecology and Systematics, 28, 621-658.

Robertson, A.I. (1997) Land-water linkages in floodplain river systems: the infleunce of domestic stock. In: Frontiers in Ecology: building the links (eds N. Klomp & I. Lunt). Elesevier Science, Oxford.

Robertson, A.I., Bunn, S.E., Boon, P.I. & Walker, K.F. (1999) Sources, sinks and transformations of organic carbon in Australian floodplain rivers. Marine & Freshwater Research, 50, 813-829.

Walker, K. F. & Thoms, M. C. (1993) Environmental effects of flow regulation on the lower River Murray, Australia. Regulated Rivers: Research and Management, 8, 103-119.