Evaluation of the threat from sea-level rise to the mangrove ecosystems in Tieshangang Bay, southern China

Study Number

106

Author

Shasha Li, Xianwei Meng, Zhenming Ge, and Liquan Zhang

Abstract

Sea-level rise caused by global climate change has significant impacts on coastal zones. Mangrove ecosystems occur in the intertidal zone along tropical and subtropical coasts and are particularly sensitive to sea-level rise. We used the coastal zone of Tieshangang Bay, southern China, as a case study to evaluate the threats from sea-level rise to the mangrove ecosystems. The evaluation based on the projection of sea-level rise rates from present trend (2.9 mm/yr) and RCP4.5 scenario (0.53 m sea-level rise by 2100) of the Intergovernmental Panel on Climate Change’s Fifth Assessment Report, were performed for 2025, 2050 and 2100 using Sea Level Affecting Marshes Model. The results showed that the scenario using the present trend in the rate of sea-level rise would result in a 9.3%, 9.6% and 18.2% loss of mangrove habitats at the study area in 2025, 2050 and 2100, respectively. Under the IPCC’s RCP4.5 scenario, however, the higher sea-level rise rate could result in a 11.1%, 12.2% and 25.2% loss of mangrove habitats in 2025, 2050 and 2100, respectively. The SLAMM employed was able to project the spatially explicit threats of sea-level rise on the coastal mangroves in the study area. Without proper mitigation options, the potential decrease and loss of mangrove habitats and ecosystem services in Tieshangang Bay is inevitable. Based on the results of this study, mitigation measures should be considered for securing the mangrove ecosystems, including managing sedimentation and controlling reclamation and rehabilitation.

Main Results and Conclusions

• Mangrove ecosystems, which provide ecological services including coastal protection from storms and high tides, nursery habitat for ecologically and economically vital fish species, and carbon sequestration, are becoming increasingly threatened by rising sea levels resulting from climate change.
  • “[…Sea levels on the Guangxi coast in China have been rising at a rate of 2.9 mm/yr over the past 40 years, and the process is predicted to increase 60 – 120 mm in the next 30 years” (1).
  • “Using the upper limit of the IPCC scenarios of sea-level rise (0.23 – 0.59 m by 2100), Gilman et al. (2006) predicted a 13% decline in the extension of mangrove forests of the Pacific islands by 2100. Similarly, Alongi (2008) projected that climate change might lead to a global loss of 10 – 15% of mangrove forests” (1).
• Short-term projections of mangrove loss (2007-2025) suggest that ecosystems in the high intertidal zone will become inundated by water in areas where sedimentation rates are relatively low.
  • “By 2025, the change percentage of the mangrove communities located in the lower, middle and higher intertidal zones is predicted to be 9.2%, 8.2% and 12.9%, respectively, under the present trend scenario” (3).
  • “Under the RCP4.5 scenario, the change percentage of the mangrove communities located in the same zones will reach 11.6% (lower), 8.6% (middle) and 13.3% (higher), respectively, which will result in a 11.1% area loss of mangrove habitats” (3).
• Medium-term projections of mangrove loss (2007-2050) reveal a similar pattern.
  • “By 2050, the change percentage of the mangrove communities located in the lower, middle and higher intertidal zones is predicted to be 9.6%, 8.3% and 13.0%, respectively, under the present trend scenario” (3).
  • “Under the RCP4.5 scenario, the change percentage of the mangrove communities located in the same zones will reach 11.9% (lower), 11.4% (middle) and 16.1% (higher) respectively, which will result in a 12.2% area loss of mangrove habitats (Table 3)” (4).
• Long-term projections of mangrove loss (2007-2100) showed the greatest loss of area particularly at sites with little uplift and sediment deposit.
  • “By 2100, the change percentage of the mangrove communities located in the lower, middle and higher intertidal zones is predicted to be 19.7%, 13.4% and 19.5%, respectively, under the present trend scenario” (5).
  • “Under the RCP4.5 scenario, the change percentage of the mangrove communities located in the same zones will reach 21.2% (lower), 33.5% (middle) and 34.0% (higher), respectively, which will result in a 25.2% area loss of mangrove habitats (Table 3)” (5).
• Local preservation efforts are being implemented with the help of the Chinese government.
  • “In 1990, a national nature reserve (Shankou National Mangrove Nature Reserve) was established, and this plays an important role in protecting mangroves and preventing reclamation” (7).
  • “The dredged sediment can be used to recreate mudflats and establish pioneer mangrove vegetation, to promote sedimentation by slowing flow and reducing wave energy (Lin, 1997; Kumara et al., 2010)” (7).
• The continued construction of sea walls and reclamation for aquaculture prevents mangroves from migrating further up the intertidal zone in response to sea level rise and alters natural sedimentation and erosion rates along the coastline.
  • “Without proper mitigation, the potential decrease and loss of mangrove habitats and their associated ecosystem services in TB is inevitable” (7).
  • “This large-scale reclamation has exacerbated the loss of coastal mangroves and has made the remainder more vulnerable to sea-level rise” (7).