Percent of agricultural land

The percentage of catchment area under intensive agriculture (cropping, improved pastures) in Australia's Intensive Landuse Zone was used as an indicator in the assessment catchment condition, during the National Land and Water Resources Audit [1].

Photo 1. View of agricultural areas in the Tweed River catchment (photo by David Heggie).

Issues arising from intensive agriculture

'Percentage land area under intensive agriculture' was developed to address habitat loss and biodiversity issues in catchments [2].

Nitrogen export to coastal waterways should also increase as the proportion of cropping and grazing land in a catchment increases. This has been shown to be the case in the watersheds of Chesapeake Bay, and is mainly due to fertiliser usage [3]. Coastal waterways with a significant proportion of agricultural land in their catchments should also be subject to diffuse loads of pathogenic organisms (from animal manures) and pesticides, and to eroded soils transported as suspended sediment (especially if agriculture is on steep slopes).

Therefore, issues that may arise in coastal waterways with significant agricultural areas in their catchments are:

• eutrophication and related problems such as algal blooms, anoxic & hypoxic events, fish kills and shellfish closures;
• increased loads of fine sediment; and
• exposure of organisms to toxicants.

These factors, and the physical removal critical habitat areas, can contribute to an overall reduction in biodiversity.

Existing information and data

More information and maps of 'Intensive Agriculture' can be found at the Catchment Condition Online Maps website [2]. Appendix I (pp. 311-312) in Volume 2 of the Australian Catchment, River and Estuary Assessment, 2002 contains a map of Australia's River Basins and Drainage Divisions in which each river basin has been assigned a number. These catchment numbers can be matched to a large number of coastal waterways in pages 316-363 of the same document. The percent are under 'Intensive Agriculture' for a large number of river basins are available in Appendix B (pg 65-76) of the Assessment of Catchment Condition in Australia's Intensive Land Use Zone: A biophysical assessment at the national scale [1].

References

1. The assessment of catchment condition was conducted as a partnership between the Audit, the Bureau of Rural Sciences and CSIRO Land and Water with support and involvement of State and Territory natural resource management agencies. The final report (Project 7/8) to the National Land and Water Resources Audit by Walker, J., Veitch, S. Braaten, R., Dowling, T., Guppy, L., Herron, N (2001) is entitled Assessment of Catchment Condition in Australia's Intensive Land Use Zone: A biophysical assessment at the national scale and is found at the following website: www.affa.gov.au/content/publications.
2. Catchment Condition Online Maps website at Agriculture, Fisheries & Forestry Australia.
3. Jordan, T.E., Correll, D.L. and D.E. Weller. 1997. Effects of agriculture on discharges of nutrients from coastal plain watersheds of Chesapeake Bay. Journal of Environmental Quality 26, 836-848.