Nitrogen and phosphorus are essential nutrients for all forms of life. However, high levels of these substances pose an environmental hazard. High concentrations of total nitrogen and total phosphorous are often associated with algal blooms (including toxic blue-green algal blooms), as well as dense aquatic plant growth. This process of high nutrient input and algal growth is know as eutrophication, which can lead to water that does not support aquatic life. Emissions of nitrogen and phosphorus are estimated to be lower to the Derwent catchment than to the Tamar/Esk catchment.
Agriculture and sewage treatment plants are estimated to generate the largest amount of phosphorous to both the Derwent and Tamar/Esk catchments. The highest estimated emissions of nitrogen in to the Derwent and Tamar/Esk catchments, are estimated to be from agriculture, woodland and sewage treatment plants.
ESTIMATED ANNUAL EMISSIONS OF NITROGEN AND PHOSPHORUS, Derwent and Tamar/Esk water catchments(a)
|
 | Derwent(b)
| Tamar/Esk(b)
|
| Total
nitrogen | Total
phosphorus | Total
nitrogen | Total
phosphorus |
| | | |
|
| tonnes/year | tonnes/year | tonnes/year | tonnes/year |
|
| Agriculture | 522.7 | 166.3 | 905.1 | 288.0 |
| Alpine heath | - | - | - | - |
| Alpine scrub | - | - | na | na |
| Bare(c) | 26.2 | 2.1 | 25.1 | 2.0 |
| Buttongrass | 18.3 | 1.2 | 8.6 | 0.8 |
| Fish farm (aquaculture) | 18.8 | 1.8 | na | na |
| Forest | 194.2 | 19.4 | 123.9 | 12.4 |
| Rainforest | 77.4 | 7.7 | 23.2 | 2.3 |
| Scrub | 44.5 | 4.5 | 19.5 | 2.0 |
| Sewage treatment plant(d) | 470.9 | 147.9 | 312.0 | 116.7 |
| Suburb | 11.6 | 2.1 | 11.8 | 2.2 |
| Urban | 16.9 | 3.1 | 22.6 | 4.2 |
| Woodland | 244.6 | 24.5 | 418.1 | 41.8 |
| Non reporting facility(e) | 13.0 | - | na | na |
| Total | 1,659.2 | 380.6 | 1,870.0 | 472.4 |
- nil or rounded to zero
na not available
(a) Data derived using best estimate methodologies, not direct measurement. Accuracy of data will vary according to the estimation technique used.
(b) The National Pollutant Inventory (NPI) is an Internet database designed to provide the community, industry and government with information on the types and amounts of certain substances being emitted to the environment. NPI water catchments cover rectangular areas with the following boundaries:
The Tamar/Esk water catchment extends as far west as Deloraine, as far south as Longford, and as far north-east as East Sandy Point, near Bridport.
The Derwent water catchment extends as far north as Bagdad, as far east as Dodges Ferry, as far south as the southern-most tip of Betsey Island, and as far west as Hayes, near New Norfolk.
(c) No vegetation cover.
(d) Sewage treatment plant data available for 2001-02. All other Derwent estimates were available for 1998-99. All other Tamar/Esk estimates were available for 1999-2000.
(e) A facility that is exempt from or chooses not to report activity.
Source: National Pollutant Inventory Database http://www.npi.ea.gov.au, Department of Primary Industries, Water and Environment. |
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