Mangrove Trail #2 Human Impacts Traditional Cache

Time to pack the Kayak, Sunscreen, Insect repellent, plenty of water and enjoy day on the water Kayaking along the Port River Mangroves enjoying the sights and sounds and smells, This trail will take you towards St Kilda looping back and ending back close to the beginning, with luck you will see the Fish and Animals mentioned in the series, each listing will cover information on the Mangroves and different animals that live in or can be found around the Mangroves.

HUMAN IMPACTS

The close proximity of human settlement with mangroves often creates problems that result in further loss of mangrove area. Most tidal wetlands in the northern ends of the Gulfs, and Barker Inlet in Port Adelaide, are severely altered by coastal development. Over 90% of the population live near the coast with the majority in the Adelaide region where mangroves occur. Increased sedimentation associated with coastal strip development may explain the mangrove expansion at around five hectares per year in Barker Inlet. There has been contamination of marine sediments by heavy metals from the lead smelter in Port Pirie and the Whyalla steelworks, with further contamination from salt and chemical works near Adelaide and northern Spencer Gulf. Eutrophication has resulted from urban stormwater runoff and sewage discharges, especially around Adelaide and northern Spencer Gulf, causing the proliferation of nuisance macroalgae (Ulva) that smothers mangrove roots and seedlings. Around 250 ha of mangroves have died near the outfall of Adelaide’s Bolivar sewage treatment plant, and since 1954, 25% of mangroves were lost in Gulf St. Vincent. Oil spills, notably that in 1992 near Port Bonython in northern Spencer Gulf, have affected nearly 100 ha of mangroves and 23 ha have died. Uncontrolled public access to mangrove areas has resulted in severe stem damage from trampling of roots and this will take several decades to recover, if at all.

NATURAL CHANGES

Seaweed covering pneumataphoresSeagrass detritus covering and smothering pneumatophores of Avicennia marina. Photo: Sabine DittmannSouth Australian mangroves are exposed to various extreme conditions by: a dry climate, high salinities in coastal waters, and broad coastal areas exposed to large waves. Various natural factors are indicative of changes taking place. In the case of sea level rise, levee banks and salt ponds may prevent the landward retreat of mangroves in some areas. Seagrass detritus washed into mangroves areas will smother pneumatophores and juvenile plants. Coastal erosion, saltation and dune encroachment have lead to the some loss of mangroves.