Saltmarsh Mangroves are characterised by depositional coastal environments where fine sediments collect in areas protected from high energy wave action. Factors driving Saltmarsh Mangrove ecosystems are 3-fold - geological (rock, sand and sediment), Hydrological (nearshore currents, tides) and continental proximity (nutrient Imput and anthropogenic impacts).
The NSW Coast is a high wave energy coastline, so mangroves are confined within sheltered embankments and estuaries. Of the 133 estuaries and coastal creeks in the state, 69 contain mangroves, covering a combined area of 107km2. The Central Coast region is characterised by sandstone bedrock coastlines with numerous drowned river valleys, including the Hawkesbury River (and tributaries). The geology in this area comprises Of Terrigal Formation and Hawkesbury Sandstone formations of the Triassic age; and the soil is mostly of the Erina soil landscape type, all of which have High erosion potential once exposed. The Narara Creek catchment is within a generally sandstone mountainous/hilly area with numerous creeks draining the hills, flowing into the valley. The long term alluvial sediment accumulation, and the nearby tidal creeks have created the conditions for a Mangrove community to thrive in this area. On close examination, the basins of the valley have been found to have a deep mantle of soil materials with varying amounts of ironstone gravel, secondary quartz and siderite. Where once it was possible to enter the mouth of Narara Creek here, sediment rich run off in the creek catchments has created a dense area of mangroves, consisting mostly of Avicennia Marina and Aegiceras Corniculatum.
Mangroves and tidal communities are amongst the most endangered marine wetland habitats worldwide. The shift from saltmarsh to mangrove dominance on subtropical and temperate shorelines has important implications for ecological structure, function and global change adaptation. Erosion undercuts the mangrove trees and shrubs resulting in their loss, and the deposition of sediments buries the breathing roots, resulting in suffocation of trees.
For this reason, please remain on the boardwalk, and if you are willing and able, please perform CITO where possible in this area.
EarthCache - Logging Requirements:
Please visit the site and walk the length of the boardwalk - please take note of the 3 information boards along the way.
If you would like to, please post a photo (or several) with your log - either of the mangroves, or the view from the posted coordinates.
Please email the CO with your answers to the following questions:
1. What made it impossible to pass through the mouth of Narara Creek?
2. What geological characteristics make the Central Coast region suitable for Mangrove Communities?
3. What creates the high salinity in the Saltmarsh?
Please also comment on the condition of the mangroves in your log - can you see the damage from the oil spill, or evidence of further damage to the mangroves?
*Please note, you do not have to wait for approval from the CO to log your find, and you may do so as soon as you have sent your email, however logs may be deleted if no verification email is received.