Rivers - Nutrient Loads and Transport - Tasmania

Tasmania

Increases in river nutrient loads generally lead to increases in the production of algae and aquatic plants, with follow-on effects up the aquatic food chain. Large nutrient increases typically favour a small number of species at the expense of others, and so while overall system productivity is increased, biodiversity is reduced. The reduced diversity of species is often associated with reduced system resilience, and catastrophic collapses are common. Such collapses may include the death and decay of large algal blooms, thereby increasing biological oxygen demand, lowering dissolved oxygen levels and leading to massive fish kills and high mortality amongst other river fauna (see Australian Catchment, River and Estuary Assessment 2001 for the Audit river and estuary assessment).

River nutrient budgets for phosphorus and nitrogen allow determination of:

major sources of nutrients to rivers;
major loss pathways for nutrients transported through river systems; and
major loss pathways for nutrients transported through river systems; and

They are linked to landscape nutrient budgets, because erosion and surface run-off are important pathways for nutrient loss from the landscape. An understanding of the fate of nutrient lost from landscapes and ecological responses to nutrient loads in the receiving waters, can help guide land and water planning and management.

Use of a modelling approach, combines outputs from erosion and river sediment transport modelling, with landscape? plant? soil? atmosphere? nutrient flux modelling and point source discharge data. River nutrient transport modelling considers dissolved nutrients that are associated with suspended sediments. Exchanges between these forms are modelled for phosphorus. Losses from transport include:

fine sediment deposited in reservoirs and on floodplains; and
denitrification of dissolved nitrogen to nitrogen gas.

Rivers nutrient loads and transport assessment

Agricultural and urban disturbance within a catchment leads to increases in nutrient exported to the river systems. These increased nutrient loads affect river ecosystems, usually in undesirable ways. Assessing changes in nutrient loadings is therefore an important aspect for assessing river condition, and one that highlights the linkages between a river and its catchment.

Assessing river nutrient load is complex, either using measured data or by modelling, because of the complex processes involved in nutrient sourcing and transport, and the high temporal variability of river flow. Process modelling is usually carried out in conjunction with detailed daily hydrology modelling. However, this is not required for broad-scale assessments of changes, and in any case sufficient data are often not available.

A model of river nutrient transport (Annual Network Nutrient Export or ANNEX?see next section) was developed to predict current and pre-disturbance nutrient loads in Australian rivers

Annual Network Nutrient Export (ANNEX)

Sums nutrient sources delivered to each link of a river network, and accumulates the consequent loads to determine average annual exports.

Combines soil nutrient concentrations from Australian Soil Resources Information System with estimates of average annual sediment loads from SEDNET modelling to estimate the average annual nutrient loads to rivers associated with water erosion.

Combines estimates of average annual nutrient loads for surface run-off from BIOS modelling with point source data from the National Pollutant Inventory (www.environment.gov.au/epg/npi/database/database.html) to estimate the average annual loads of dissolved nutrient to rivers.

Annual Network Nutrient Export considers the following nutrient source terms at each network link:

sediment-attached nutrients from hillslope erosion (from SEDNET)

sediment-attached nutrients from gully erosion (from SEDNET)

sediment-attached nutrients from river channel bank erosion (from SEDNET)

dissolved nutrients in surface run-off and sub-surface drainage (from BIOS)

point source nutrient discharges (from National Pollutant Inventory database)

Nutrients are transported in both dissolved and sediment-attached forms. The model assumes that the:

sediment-attached nutrient load is associated with the clay fraction of the sediment being transported entirely in suspension; and

capacity for transport of nutrients both in dissolved forms and associated with suspended sediments is unlimited.

Rivers nutrients in Tasmania

River basin name	Total nitrogen exported (t/yr)	Total Phosphorus exported (t/yr)	Nitrogen delivered to estuaries (%)	Phosphorus delivered to estuaries (%)
Arthur River	33,010	4,489	99	99
Coal River	17,280	2,233	79	74
Derwent River	29,500	3,733	88	85
East Coast	22,610	3,116	92	87
Flinders - Cape Barren Islands	11,020	1,764	No Data	No Data
Forth River	42,640	5,264	90	94
Gordon River	25,960	3,466	91	94
Huon River	26,620	3,345	99	99
King Island	12,350	2,211	No Data	No Data
King-Henty Rivers	36,330	4,283	94	96
Kingston Coast	21,420	2,710	99	100
Mersey River	43,300	5,516	96	96
Pieman River	34,890	4,258	91	99
Piper-Ringarooma Rivers	27,610	3,787	95	94
Rubicon River	27,940	3,972	97	95
Sandy Cape Coast	15,570	2,359	99	99
Smithton-Burnie Coast	31,850	4,537	98	98
South-West Coast	16,680	2,428	98	99
Tamar River	30,900	4,051	91	88

Click on the river basin name or map below to view a report on the nutrient - sediment - landscape budget terms.

Map of TAS's river basins

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

Key

Links to an another web site
Opens a pop-up window

Australian Natural Resources Atlas

Rivers - Nutrient Loads and Transport - Tasmania

Tasmania

On this page