Mary River Wetlands
The Mary River is located 90kms east of Darwin in the Northern Territory with a catchment that covers an area of 8100 km2 with predominately freshwater wetlands extending over approximately 1,300 km2.
It is a highly productive area which supports multiple land uses as well as providing habitat for a large range of wildlife, including saltwater crocodile Crocodylus porosus, magpie goose Anseranas semipalmata and barramundi Lates calcarifer. The freshwater floodplains are a variable environment with seasonal changes in vegetation cover and species composition due to the contrasts between freshwater inundation during the wet season and retreating water levels during the dry season.
The wetlands provide an important spatial and temporal mosaic of wildlife habitats and for this reason the Mary River wetlands is listed in the Directory of Important Wetlands (ANCA 1996). Compared to most other coastal rivers in the Northern Territory, the Mary River displays uniqueness in not having any major tidal estuary as a river outlet for at least the last 2,000 years.
Until recently the wet season runoff from the river’s 8,000 km2 catchment emptied into extensive lowland and floodplains which are dissected by deep unconnected billabongs and braided channels. The floodplains and billabongs were separated from the sea by a series of parallel narrow sandy chenier ridges which are a legacy of the receding shoreline over the last 6,000 years.
The Mary River wetland supports a variety of land use activities including pastoralism, recreational and commercial fishing, tourism, mining and defence force training. Pastoralism is the main activity which accounts for more than 60% of the catchment area. The pastoral industry on the lower floodplains, both for buffalo and cattle grazing has an estimated value of $17.5m per annum.
The saltwater damaged floodplains have resulted in an estimated cost to the pastoral industry of approximately $4.9M per annum. The area is also particularly important to recreational fisherman due to its close proximity to Darwin and its high barramundi population. The recreational fishing industry has an estimated value of $5m per annum.
The productivity of the fishery is directly proportional to the abundance of freshwater nursery habitat and any negative impacts from salt water intrusion are detrimental to its productivity. Tourism is another major activity with an estimated value of $6m. A base value of 11,000 visitors to the Mary River was used to calculate net worth but forecasts for tourist growth are for a two fold increase in visitation to the area over the next decade.
A Cost-Benefit Analysis of Mary River Salinity Mitigation was undertaken in June 2003, funded by the Australian Greenhouse Office and managed by the Northern Territory Greenhouse Unit. To date the stimated value of ecosystem services is in the order of $6m.
