Derwent Estuary program
After the colonisation of Tasmania in 1803, the British established themselves on the Derwent Estuary, with the first official ferry crossing in 1814.
Colonisation had significant impacts on the Derwent Estuary, particularly through whaling and industrial pollution.
In 1856 the last whale to be seen in the estuary was harpooned. It would be a hundred years before whales came back to the River Derwent.
The early 1900s saw industrialisation grow along the riverbanks, with the establishment of an electrolytic zinc smelter and later a paper mill.
Heavy metals entered the Derwent estuary due to industrial practices, before modern environmental standards were established.
Sadly, environmental contamination levels in the Derwent have been recorded as amongst the highest in Australia. However, whilst this pollution remains high, recent monitoring has revealed a gradual reduction and improvement.
The Derwent Estuary Program, starting in 1999, was a partnership between state and local government and is focused on the restoration and promotion of the Derwent Estuary and its unique habitats and species that reside there.
It is designed to mitigate further losses and work with the community to build the overall health of the estuary, with hopes of recovering what was lost.
There have been four central themes identified to help achieve a restored and promoted Estuary, including:
- Managing human pressures,
- Protecting ecosystems,
- Enhancing human uses,
- Promoting understanding,
- awareness and participation.
The successful outcomes of the Derwent Estuary Program so far have been to manage and reduce pollution and improve the water quality at beaches.
Microphyte beds
The macrophyte beds of the mid to upper Derwent Estuary are dense and extensive, covering an area of over 600 hectares. These macrophyte beds provide important ecosystem services including nutrient cycling, water-column filtration, sediment stabilisation, coastal protection and sequestration of atmospheric carbon. They are the main food source for the large population of Black Swan and other waterbirds that inhabit the area. The macrophyte beds are important habitat for recreationally and ecologically important fishes including Black Bream, Brown Trout, whitebait, Yelloweye Mullet, and the threatened Australian Grayling.
The macrophyte beds are dominated by the rare aquatic macrophyte Ruppia megacarpa, which prefers shallower, lower salinity areas. Species diversity is greatest at Dromedary Marsh and Murphys Flat, other species of macrophyte observed include Ruppia polycarpa, Lepilaena clyindrocarpa, Lepilaena patentifolia (described once in the Derwent) and Nitella hyaline (only the second observation in Tasmania). The brackish seagrass Zostera mulleri, is observed in small patches on the edge of the river channel.
Seasonally in spring and summer when water temperatures increase and there are elevated nutrients in the water column these macrophyte beds can be covered in epiphytic algal growth. This smothering of the macrophyte plants can lead to significant dieback of the beds. Routine monitoring of upper estuary macrophyte bed condition by the Derwent Estuary Program found that despite stressors and several significant die back events in recent years these macrophyte beds are resilient and able to recover back to dense levels of cover.
For more information visit:
References:
- Murray. M. 2024. Black Swan. https://australian.museum/learn/animals/birds/black-swan/.
Derwent Estuary Program. Species of the Derwent. - https://www.derwentestuary.org.au/species/black-swan/. Accessed on 17 Sept. 2024.