Evaluation of mangrove rehabilitation project at Carey Island coast, Peninsular Malaysia based on long-term geochemical changes

Abstract

A project for mangrove rehabilitation purpose has been carried out at intertidal area of Carey Island, Peninsular Malaysia in early 2009. As part of the project, a detached low-crested breakwater has been constructed near the bare degraded mangrove area to reduce wave energy and storm surges forcing the site. The breakwater is also expected to trap the sediment behind its structure as well as soil nutrients needed for mangrove seedling. This study attempts to evaluate the changes of seabed elevation and geochemical in soil around the degraded mangrove area after 6 years implementation of the breakwater's structure. Seabed elevations at degraded mangrove area (rehabilitated area) and concentration of soil nutrients at three locations (rehabilitated area, non-rehabilitated area and natural forest area) were monitored on October 2015. The seabed elevations on October 2015 are compared to the seabed elevation in January 2009 to determine the seabed level changes. In addition, the values of soil nutrients at rehabilitated area were compared to soil nutrients at non-rehabilitated area and natural mangrove forest to evaluate the geochemical condition of soil at mangrove degradation area for preparation of mangrove seedling planting. The results present that there is an increment of seabed elevations at the degraded mangrove area after 6 years construction of the breakwater (approximately 32 cm in average). The results also show a significant increase in the amount of soil nutrients on the top soil (approximately 0 to 20 cm depth) especially carbon, nitrogen and potassium at degraded mangrove area with almost similar to soil nutrients in natural mangrove forest. It demonstrate that the condition of degraded mangrove area after 6 year implementation of the breakwater is conducive for replanting the mangrove seedlings to restore the endangered mangroves at intertidal area of Carey Island, Peninsular Malaysia.