Australian Natural Resources Atlas

Rivers - Nutrient Loads and Transport - Northern Territory

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Northern Territory

Rivers - nutrient loads and transport

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:

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:

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 Northern Territory

    River basin name

    Total nitrogen exported (t/yr)

    Total Phosphorus exported (t/yr)

    Nitrogen delivered to estuaries (%)

    Phosphorus delivered to estuaries (%)

    Adelaide River3,232476No DataNo Data
    Barkly940164No DataNo Data
    Bathurst and Melville Islands4,043738No DataNo Data
    Blyth River2,108385No DataNo Data
    Buckingham River2,535492No DataNo Data
    Burt1,225208No DataNo Data
    Calvert River1,378243No DataNo Data
    Daly River2,267353No DataNo Data
    East Alligator River2,413422No DataNo Data
    Finke River895147No DataNo Data
    Finniss River3,234515No DataNo Data
    Fitzmaurice River1,988336No DataNo Data
    Georgina River695125No DataNo Data
    Goomadeer River2,048370No DataNo Data
    Goyder River2,100372No DataNo Data
    Groote Eylandt1,898361No DataNo Data
    Hay River49790No DataNo Data
    Keep River1,431245No DataNo Data
    Koolatong River2,482484No DataNo Data
    Limmen Bight River1,011191No DataNo Data
    Liverpool River1,791328No DataNo Data
    Mackay706143No DataNo Data
    Mary River (WA)2,787430No DataNo Data
    McArthur River1,040196No DataNo Data
    Moyle River2,959450No DataNo Data
    Nicholson River1,114194No DataNo Data
    Ord River1,158201No DataNo Data
    Robinson River1,206223No DataNo Data
    Roper River1,513260No DataNo Data
    Rosie River1,133221No DataNo Data
    Settlement Creek1,685276No DataNo Data
    South Alligator River2,183357No DataNo Data
    Todd River831141No DataNo Data
    Towns River1,107218No DataNo Data
    Victoria River1,516245No DataNo Data
    Walker River1,662321No DataNo Data
    Warburton856160No DataNo Data
    Wildman River3,132515No DataNo Data
    Wiso868164No DataNo Data

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

    Map of NT's river basins

    Further Information

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