Coastal terrestial systems and sea-level rise: appendix 7

Abstract

Based on limited monitoring, experiments and modelling of climate change outcomes, relative sealevel rise may be the greatest future threat to tidal wetlands and beaches. Reduced coastal ecosystem area and condition will increase coastal hazards to human settlements, reduce coastal water quality, release large quantities of stored carbon, and eliminate nesting, nursery and forage habitat for numerous species groups, including fish, shellfish, seabirds, waterbirds, sea turtles, crocodiles, manatees and dugongs. n Rising seas will likely have the greatest impact on coastal wetlands experiencing net relative lowering in sediment elevation, and where there is limited area for landward migration due to the physiographic setting or obstacles from development. The majority of mangrove sites studied have not been keeping pace with current rates of relative sea-level rise, this exceeding the observed mean change in mangrove sediment surface elevation of +1 mm a–1. As a result, 0.2% annual reductions in Pacific Islands region mangroves are predicted over this century, contributing about 10 to 20% of total estimated losses. n Longer-term monitoring of coastal ecosystem changes from a larger number of regions is needed for evaluation of ecosystem resistance. There is a need for reliable predictive sediment elevation models and models of coastal ecosystem erosion. There is also a need for improved understanding of the synergistic effects of multiple climate change and other anthropogenic and natural stressors on coastal ecosystems. n Adaptation options, to offset anticipated coastal ecosystem losses and improve resistance and resilience to rising seas, include: coastal planning to facilitate landward migration; ‘no regrets’ reduction of stressors, including catchment management to minimize disturbance to sedimentation processes; rehabilitation of degraded areas; and increases in protected areas that include functionally linked coastal ecosystems. Establishing coastal ecosystem monitoring through regional networks using standardized techniques enables the separation of site-based influences from global changes, improving the understanding of coastal ecosystem responses to sea level and global climate change, and alternatives to mitigate adverse effects.