Control Options

Maintain/Restore Ecosystem

Submerged macrophytes

Submerged macrophytes include aquatic plants and plant-like macroalgae such as charophytes. Where they are present, macrophytes perform several important functions within a wetland, including the removal and storage of nutrients from the water column and sediment which decreases the nutrients available for phytoplankton growth, reduction of sediment re-suspension which reduces nutrient release into the water column (Carpenter and Lodge 1986) and provision of a structural habitat for fish and macroinvertebrates, including those that prey on midge. Eutrophication has been implicated in the decline of submerged macrophytes and an increase in nutrients can result in a switch from a clear water, macrophyte-dominated system to a turbid, phytoplankton-dominated system (Scheffer 1989). In wetlands where macrophytes occur, preservation should be an important management priority. Recognition of the importance of macrophytes in wetland systems has led to recent work on the restoration of submerged macrophytes in southern Western Australian rivers and wetlands. Mykytiuk (2003) identified substrate type, poor water quality, competition with exotic species such as Typha orientalis and grazing by birds as important factors affecting macrophyte restoration in wetlands on the Swan Coastal Plain. Novak (2004) reported that macrophyte re-establishment may be possible in south west rivers in association with nutrient remediation using Phoslock™.

Fringing vegetation

Fringing vegetation is an important component of freshwater ecosystems. Shading of the littoral zone by fringing vegetation decreases the amount of light and subsequent algal production in the water column and inhibits elevated temperatures that favour accelerated midge production. Emergent vegetation such as rushes and sedges help to filter nutrients and provide habitat for macroinvertebrates, frogs and fish. Fringing vegetation is also an important source of humic substances. These consist of dissolved organic carbon and give many of the wetlands located on areas of Bassendean sand, on the Swan Coastal Plain their characteristic ‘dark tea’ colour. Coloured wetlands on the Swan Coastal Plain typically have a low phytoplankton biomass despite high nutrient concentrations (Davis et al. 1993) which is primarily due to light limitation. Davis (1993) suggested that there is a potential to add colour (humic substances) to clear, eutrophic wetlands to control or reduce algal blooms. Delfs (2002) and Da Silva (2003) investigated the use of MIEX regenerant, a by-product of water treatment produced by the Water Corporation of Western Australia, to restore colour to clear eutrophic wetlands. However, MIEX in its present form was found to have nutrient concentrations that promoted phytoplankton growth (Delfs 2002), and to have levels of salts that were unacceptable for the addition to freshwater ecosystems (Da Silva 2003).

Back to Control Option Model

Updated : 23 June, 2009