Extended dry seasons over several years combined with changed cattle production systems have placed increased pressure on native pastures across northern Australia. Over the past twenty years stocking rates in some areas have begun to exceed 'safe' carrying capacities resulting in undesirable changes in pasture composition, and soil degradation. The increases in grazing pressure have coincided with an increasing awareness that the changed processes in the land that lead to pasture and soil degradation, can also affect water quality of the catchment. There is particular concern about the off-shore effects that changes in river water quality may be having. Such effects may involve, for example, increased sediment and nutrient inputs degrading the estuarine breeding grounds of commercia! fisheries or changing the ecology of coral reefs. This concern is illustrated by the several conferences and workshops that have been held to discuss the changes in, and effects of, terrigenous inputs to the Great Barrier Reef lagoon, and by the formation in Queensland of the Downstream Effects of Agricultural Practices (DEAP) committee.
There is also increasing awareness of the need for Australian industries to be productive and economically viable, but not at the expense of degrading our natural resources so as to impair their capacity for use, including use by future generations. This need has been enunciated in the principles of ecologically sustainable development. As a result of the increased awareness within the community of the need to maintain the productivity of our natural environment, there are increasing requirements for agricultural commodities to be produced so as not to cause degradation of our biota, and land and water resources. It is becoming more and more incumbent on agricultural industries to demonstrate that their management practices are not degrading the environment.
It is now well understood that catchment water quality and its implications for downstream biota and water use, are the result of all activities within a catchment. This has lead to the concept of Integrated or Whole Catchment Management and the development of catchment management groups. The aim of these groups is to develop catchment management strategies and plans to ensure that management is integrated and that the different land uses are not detrimentally affecting other industries. While the management of grazing lands must take place within a whole catchment framework, it is also essential that the off-site effects attributable to particular grazing practices be separated from those caused by other industries, or which occur naturally. By being in possession of the facts, the industry can take proper and realistic responsibility, and develop a strategic position for the future which will enhance its competitiveness, particularly internationally.
These issues are of concern to the Meat Research Corporation and the Land and Water Resources Research and Development Corporation and are being addressed in Phase 3 of the North Australia Program (NAP3). Phase 3 follows Phases I and 2, and extends from mid 1996 to mid 200 I. The North Australia Program, which is jointly funded by the Meat Research Corporation and the Land and Water Resources Research and Development Corporation, seeks to "improve the profitability, international competitiveness and ecological sustainability of beef production in northern Australia".
International competitiveness has been addressed by examining the determinants of competitiveness and concluding, among other things, that adoption of acceptable environmental standards will be fundamental to the future of the industry. Subprogram 2 ofNAP3, Improving Resource Management, aims to increase international competitiveness and hence profitability, by improving the development and adoption of ecologically sustainable resource management systems and their profitable utilization by the northern Australian beef industry.
To assist in developing a relevant program of research for NAP3, the Meat Research Corporation and the Land and Water Resources Research and Development Corporation jointly commissioned a broad overview of current information on the effects of catchment use and management in the grazing lands of northern Australia, on water and nutrient cycles and the downstream fluxes of water, sediment and nutrients. Interactions between grazing management (primarily stocking rates and their variation in time and space), drought, clearing and pasture improvement in producing these effects were regarded as particularly important. Also important were the effects of these changes on the ecological status of riverine, estuarine and marine ecosystems, although the review was not concerned with impacts upon biological diversity more generally as this has been the focus of another project within NAP3. As well as reviewing current knowledge, the commissioned review was also required to recommend work which might appropriately be funded by NAP3 and to prepare a draft report for review by a forum of northern Australian beef producers and others \\;th responsibilities in natural resource management.
A large amount of research relevant to this topic has been undertaken and it was not possible in the time- frame available to comprehensively review all material. The aim has been to identify major gaps in understanding and kno\'/ledge. Most research to date has involved understanding the effects of particular stocking regimes on pasture composition and water, sediment and sometimes nutrient fluxes. Generally, this work has been for plots or small catchments. There has also been some work identifying the effect of clearing and pasture improvement on components of the water balance. The terrestrial inputs from catchments flowing into the Great Barrier Reef lagoon, the fate and effect of these inputs, has also received some attention. Estimations of terrestrial inputs and their change follo\\;ng the introduction of grazing, have been based on fluxes measured for plots or small catchments or on extrapolations from rivers and streams for which sediment concentration and flow data are available. A very limited amount of work is currently unden\'ay using coral and sediment cores to investigate temporal changes in terrestrial inputs from catchments on the east coast of Queensland. The issue of the degree to which the introduction of grazing has increased sediment and nutrient fluxes to the marine environment over and above natural inputs, and the effect of this increase, particularly on the Great Barrier Reef remains equivocal.