Freshwater and mangrove habitats: issues in GBR catchments and the Torres Strait - Damien Burrows

Freshwater coastal wetlands and mangrove habitats provide a variety of ecosystem services include flood protection, erosion control, wildlife food and habitat, commercial fisheries, water quality, recreation and carbon sequestration1. An ecosystem service may be defined as “the benefits people obtain from ecosystems”2.

Unfortunately these areas are under threat World-wide, from rural development and agriculture as well as erosion and inundation from sea level rise and increasing storm frequency3.

Dr Damien Burrows of TropWATER4 (JCU) gave an overview of the issues facing GBR and Torres Strait wetlands and mangroves, particularly as a result of anthropogenic changes. Pesticides, excess nutrients and sediments flow into these areas, altering the habitat and ecology and, within wetlands, road and bund development creates barriers to water flow and fish passage. Loss of native riparian vegetation and the rise of introduced floating and emergent aquatic weeds were discussed, as was damage caused by feral animals (fish and mammals).

The Burdekin coastal wetlands were used as an example with one of the main threats the coverage of lagoons by floating weeds such as water hyacinth. This Class 2 Pest Plant was originally introduced to Australia as an aquatic ornamental but has since become a major pest of rivers and dams5. Mats of the weed destroy native habitat, decreasing biodiversity, seriously depleting water of oxygen, increasing water loss and providing breeding grounds for mosquitoes6. Dr Burrows suggested that removal was the only effective means of control; killing the weed and leaving it to decay only exacerbates the problem.

The conversion of grazing land to agriculture was also seen as a threat allowing weeds such as paragrass and Hymenachne to dominate adjacent wetlands. Here Dr Burrows suggested that wetlands could be restored through grazing and fire management and displayed examples showing the effectiveness of grazing as a weed management tool.

Dr Burrow’s and his team have also been working in Torres Strait, in collaboration with Torres Strait Regional Authority Land and Sea Management Unit (TSRA LMSU) Rangers. Surveys (NERP TE Hub project 2.2) have been undertaken and knowledge exchanged with Island communities. The research shows that shoreline mangroves have been badly affected by human and other impacts. The main human-related drivers of change were seen to be clearing and cutting, the burial of roots with dredge spoilage, pollutants and fire, the latter particularly in freshwater wetlands. Other factors included shoreline erosion, mangrove upland migration, storm damage (wind, lightning and sediment deposition) and damage by feral animals (pigs and deer) and weeds (pond apple6).

As part of the NERP TE Hub program, Dr Burrows and his team have refined their method for rapidly assessing the condition of mangrove habitats over large spatial scales (tens to hundreds of kms in days). This is achieved using boats and/or helicopters and is often conducted with the help of local community members or indigenous rangers. Dr Burrows concluded with a recent example of this, assessing the shorelines of the Burnett River in response to the recent floods where mangrove habitats have suffered extensive damage.

1  http://water.epa.gov/type/wetlands/cwt.cfm#why_imp
2  http://www.unep.org/maweb/en/Synthesis.aspx
3  http://water.epa.gov/type/wetlands/cwt.cfm#what_loss
4  https://research.jcu.edu.au/research/tropwater
5  http://www.daff.qld.gov.au/documents/Biosecurity_EnvironmentalPests/IPA-Water-Hyacinth-PP6.pdf
6  http://www.daff.qld.gov.au/documents/Biosecurity_EnvironmentalPests/IPA-Pond-Apple-PP58.pdf

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