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Rivers - Nutrient Loads and Transport - South Australia

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Millicent Coast Rivers - nutrient loads and transport

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.

River nutrient loads and 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:

• River nutrient loads and transport
• Detailed separately are:
• Couple balances of carbon, nutrients, water and productivity
• Water borne erosion and sediment 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 Millicent Coast

Attribute	Unit	Basin value	Median Australia-wide value
Basin area	km2	34,346	7,208
Improved pasture	%	41	1
Cropping	%	9	0
Horticulture	%	3	1
Total agricultural land proportion	%	53	7
Climate
Rain	mm/y	533	860
Total evaporation	mm/y	352	584
Runoff	mm/y	186	249

Nutrients delivered to rivers, floodplains, reservoirs and estuaries in Millicent Coast

Attribute	Unit	Basin value	Median Australia-wide value
Phosphorus from fine sediments	%	54	76
Phosphorus from point sources	%	0	0
Phosphorus dissolved from diffuse sources	%	46	17
Phosphorus deposited on floodplain	%	48	30
Phosphorus deposited in reservoirs	%	0	0
Phosphorus delivered to estuaries	%	52	65
Phosphorus - total basin export	tP/y	14	46
Phosphorus - export rate	kgP/ha/yr	0	0
Phosphorus load - times pre-European	ratio	2	2
Phosphorus - dissolved to total	ratio	24	21
Nitrogen from sediments	%	17	44
Nitrogen from point sources	%	0	0
Nitrogen - dissolved from diffuse sources	%	83	51
Nitrogen deposited on floodplain	%	10	16
Nitrogen deposited in reservoirs	%	0	0
Nitrogen denitrified	%	16	4
Nitrogen delivered to estuary	%	74	76
Nitrogen - total basin export	t/y	301	451
Nitrogen - export rate	kg/ha/y	0	1
Nitrogen load - times pre-European	ratio	2	2
Nitrogen - dissolved to total	ratio	83	65

Further Information

• View the Australian Agriculture Assessment 2001 report.
• View the river nutrient loads and transport chapter of the Australian Agriculture Assessment 2001 (theme) report.
• Technical reports have been prepared by CSIRO division of Land and Water in the development of this work on river nutrient loads and transport:
• View or download a technical report on " Modelling nutrient loads in large-scale river networks " by W.J. Young, I.P. Prosser, and A.O. Hughes (PDF 0.6 MB)
• a technical report on the " Regionalisations of flow variables used in modelling riverine material transport " by W.J. Young, P. Rustomji, A. O. Hughes, D. Wilkins (PDF 896 KB)
• Link to the Map Maker to make a map using this information.
• Link to the Australian Natural Resources Data Library