Mangrove Sedimentation and Response to Relative Sea-Level Rise

Abstract

Mangroves occur on upper intertidal shorelines in the tropics and subtropics. Complex hydrodynamic and salinity conditions, related primarily to elevation and hydroperiod, influence mangrove distributions; this review considers how these distributions change over time. Accumulation rates of allochthonous and autochthonous sediment, both inorganic and organic, vary between and within different settings. Abundant terrigenous sediment can form dynamic mudbanks, and tides redistribute sediment, contrasting with mangrove peat in sediment-starved carbonate settings. Sediments underlying mangroves sequester carbon but also contain paleoenvironmental records of adjustments to past sea-level changes. Radiometric dating indicates long-term sedimentation, whereas measurements made using surface elevation tables and marker horizons provide shorter perspectives, indicating shallow subsurface processes of root growth and substrate autocompaction. Many tropical deltas also experience deep subsidence, which augments relative sea-level rise. The persistence of mangroves implies an ability to cope with moderately high rates of relative sea-level rise. However, many human pressures threaten mangroves, resulting in a continuing decline in their extent throughout the tropics.

The state of the world’s mangroves in the 21st century under climate change

“…This prediction was recently borne out by large diebacks of mangroves along Australia's Gulf of Carpentaria (Duke et al, 2017) and the coast of Western Australia (Lovelock et al, 2017b) in response to a prolonged drought. Mangroves are also expected to decline along riverine systems as a result of reduced sediment supplies, increased salinities, and higher sea levels (Alongi, 2015), as have already been observed in many mangrove systems (e.g., Lovelock et al, 2015;Woodroffe et al, 2016;Meeder et al, 2017). This impact is already causing coastal erosion in the IndoPacific and the Caribbean (Lovelock et al, 2015).…”

Mangroves, fishers, and the struggle for adaptive comanagement: applying the social-ecological systems framework to a marine extractive reserve (RESEX) in Brazil

“…Landward shifts of the mangrove/marsh in the Bragança region to higher ground have been observed since 1972 and have been linked to increases in mean sea level (Lara et al 2010). Mangroves are moderately resilient to sea-level rise, but this can be compromised by human activities that disturb sedimentation processes (Krauss et al 2014, Woodroffe et al 2016. In Bragança, disturbances include the removal of crabs, altering river flows around settlements, forest degradation due to wood harvesting (Glaser et al 2003), and infrastructure development such as the road construction through the middle of the Caeté peninsula causing considerable erosion.…”

Modelling Hydrodynamic Impacts of Sea-Level Rise on Wave-Dominated Australian Estuaries with Differing Geomorphology

“…In consequence, floodplains in estuaries similar to the Shoalhaven Estuary may see considerable changes in the landscape through migration of tidal wetlands such as saltmarshes or mangroves. The broad floodplains may provide accommodation space for wetland migration [40], whereas estuaries with narrow floodplains or highly urbanised floodplains may prohibit the migration of tidal wetlands (coastal squeeze) and thus cause a loss of these valuable ecosystems [41,42]. Floodplain management in mature estuaries should consider the above and allow floodwater to enter low-lying areas in order to reduce the height of water levels in the channelised river and provide potential accommodation space for the migration and colonisation of tidal wetlands and their ecosystem services such as the mitigation of coastal flood risk [43,44].…”