Soils - Torres Strait Islands

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Torres Strait Islands

Why are material budgets useful?

The availability of light, water and nutrients determines the capacity of land to produce natural vegetation and agricultural yield. In Australia, long-term availability of resources and the consequent potential for generating yield, can be assessed by examining the mass balances of the key resources: water and nutrients (in this case nitrogen and phosphorus). Mass balance gives a quantitative picture of:

resource inflows or sources;
resource outflows (including both production outputs and unproductive losses or leakages);
the resource stock (the amount available for use); and
the way that the stock changes with time in response to the various inflows and outflows.

The mass balances of water and nutrients are linked by carbon (or biomass) since plant biomass is approximately 50% carbon. Balances and cycles of water, nitrogen, phosphorus and carbon interact and constrain each other.

The figure below provides a schematic of how the couple balances carbon, nutrients and water were constructed and linked to sediment and nutrient transport.

Erosion and sediment transport budgets

The table below presents the key material budget terms modelled or collated as part of the Australian Agriculture Assessment 2001 projects.

The budget terms cover:

water borne erosion and sediment transport.

Detailed separately are:

coupled balances of carbon, water, nitrogen and phosphorus; and
river nutrient transport

Key river basin characteristics such as broad agricultural land use categories and climate are provided for context. All attributes are presented as aggregate mass, rate, ratio or percentage estimate at a river basin scale

Context for understanding the material budgets for Torres Strait Islands

Attribute	Unit	Basin value	Median Australia-wide value
Basin area	km²	566	7208
Improved pasture	%	0	1
Cropping	%	0	0
Horticulture	%	0	1
Total agricultural land proportion	%	0	7
Climate
Rain	mm/y	1775	860
Total evaporation	mm/y	823	584
Runoff	mm/y	952	249

Water borne erosion and sediment transport in Torres Strait Islands

Attribute	Unit	Basin value	Median Australia-wide value
Sediment supplied to rivers	t/yr	no data	166621
Sediment supply	t/ha/y	no data	.5
Hill slope erosion	%	no data	14
Streambank erosion	%	no data	30
Gully erosion	%	no data	32
Length with riverbed depoistion	proportion	no data	0
Eurpoen to Pre-European sediment	ratio	no data	29
Sediment export to coast	t/y	no data	30062
Contribution of sediment to coast	t/ha/y	no data	.1
Sediment delivery	ratio	no data	.34