Abstract
This report is a summary of the 2024 Winter activities in the Blue Heart region which provides preliminary data and interpretations. This report provides evidence that the outcomes for Phase 2 have been completed. The outcomes, from Schedule 2, include: 1) the installation of RSET stations, marker beds and water level monitoring wells in the Phase 2 (River Road) site; 2) carbon measurements of cores taken in the River Road site: and 3) RSET and water level monitoring wells measurements in the Phase 1 (Coolum Creek) site.
A total of 24 RSET stations (and 72 marker beds) have now been installed in the River Road site, Coolum Creek Site and the two reference sites (Maroochy River Environment Reserve and Coolum Creek Island). Baseline measurements of nine RSET stations have been completed at the River Road (Phase 2) site in Winter 2023. Additional measurements were taken from Phase 1 Coolum Creek site and the two reference sites (15 RSET stations). The average elevation change in Phase 1 area is 11.14, 16.32 and 11.65 mm/year for the lower, moderate and higher elevation sites, respectively. This is an average of 13.03 mm/year across all three sites which is above the 10 mm/year that is estimated for sea level rise over the next 80 years. A total of 72 marker beds have been installed and up to 45 marker beds have been cored (some were still bare and not cored). These marker beds provide direct measurement of sediment accumulation thicknesses (over a given amount of time) and sedimentation rates were calculated. The average sediment accumulation rates in Phase 1 sites are 25.66, 13.62 and 6.05 mm/year for the lower, moderate and upper elevations, respectively. The reduction in sedimentation rates with higher elevation is expected with sediment being sourced from high tide flooding events and the magnitude of these flooding event will reduce with higher elevation. The average sedimentation rate is 15.11 mm/year and appears to be high enough to fill the increase in accommodation space by rising sea level (10 mm/year). The average accumulation rate exceeds the elevation change as sediment compaction will occur as more sediment weight is added to soil (subsidence = -2.08 mm/year).
A total of 16 water level monitoring wells have been install at all sites. Six new water wells were installed in the Phase 2 area and are recording hydrological conditions prior to tidal gate opening (scheduled for end of 2023). These monitors should provide insights on the initial tidal inundation once the gates are opened.
A total of 24 cores have been taken from all sites. Nine cores were taken from the Phase 2, River Road site and show carbon stock measurements of 84, 97 and 125 Mg C per hectare-metre for the lower, moderate and higher elevations, respectively. The carbon stock estimates are lower than the Phase 1 site (181 to 307 Mg C per hectare-metre) which is expected as the Coolum Creek rehabilitation site has been undisturbed for over 10 years while River Road has only recently been acquired by SCC as was pasture land (carbon poor soil compared to blue carbon). Maroochy River Environment Reserve reference site has an average carbon stock estimate of 410 Mg C per hectare-metre and this is a similar estimate as seen in other sub-tropical mangrove sites of Australia. It is expected that both Phase 1 and 2 rehabilitation areas, if mangrove forests can establish, will be able to store similar carbon stock as seen at the Maroochy River Environment Reserve reference site.
The final report is scheduled to be completed by end of May 2024, but due to the timing of 2024 winter field season, the health risk of vector borne diseases and other risks doing field work in the hotter months, we request that the final report deadline to be shift by four months to the end of September, 2024.