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150 Years of Mangrove Development in Southern China

Paper Reviewed
Xia, P., Meng, X., Li, Z., Feng, A., Yin, P. and Zhang, Y. 2015. Mangrove development and its response to environmental change in Yingluo Bay (SW China) during the last 150 years: Stable carbon isotopes and mangrove pollen. Organic Geochemistry 85: 32-41.

Writing as background for their work, Xia et al. (2015) note that mangrove forests are highly productive ecosystems with an average daily global carbon productivity of 2500 mg per square meter (Clough, 1998; Jennerjahn and Ittekkot, 2002), resulting in an annual accumulation of 26.1 Tg of organic carbon (Breithaupt et al., 2012). Consequently, mangroves play "an important role in controlling atmospheric CO2 on longer geologic time scales, due to the substantial amounts of organic matter buried in mangrove sediments (Jennerjahn and Ittekkot, 2002; Burdige, 2007; Alongi, 2008)." However, in recent years mangrove forests have declined significantly -- approximately 30 percent since 1980 -- and some projections indicate they may decline an additional 25 percent over the next decade or so as a result of human activity and climate change. And that consequence could hold still other important consequences for the global carbon cycle.

In light of the above, Xia et al. write it is important to understand the dynamics of mangrove communities and how they respond to the environmental and human development pressures they face. Focusing solely on environmental influences, therefore, the team of six Chinese researchers set out to investigate the temporal evolution of a mangrove forest community in the Shankouy Mangrove National Nature Reserve by performing a series of analyses on two sediment cores retrieved off the coast of the Shatian Peninsula, southern China (109.62-109.78°E, 21.47-21.62°N). Specifically, the aim of their study was, among other things, "to provide information on the adaptation or mortality of mangroves with past environmental change, including temperature, precipitation and sea level fluctuation" in a location "considered natural, i.e., not greatly influenced by human activity." And what did their study reveal?

According to the authors, there were two main stages of mangrove development over the past 150 years. The first stage occurred between 1870 and 1930 and represented a period of degradation. The second stage occurred between 1930 and the end of the record in 2011 and represented "a flourishing period" in mangrove development. Seeking to understand the cause of the two contrasting stages, Xia et al. compared data from their two sediment cores with climatic records, finding that the period of degradation corresponded with colder temperatures, while the flourishing period corresponded with warmer temperatures. Consequently, Xia et al. conclude that "temperature may be a key factor for the distribution and succession of mangrove communities in this region," and that factor is one in which warmer temperatures are better for mangrove development.

Alongi, D.M. 2008. Mangrove forests: resilience, protection from tsunamis, and responses to global climate change. Estuarine, Coastal and Shelf Science 76: 1-13.

Breithaupt, J.L., Smoak, J.M., Smith III, T.J., Sanders, C.J. and Hoare, A. 2012. Organic carbon burial rates in mangrove sediments: strengthening the global budget. Global Biogeochemical Cycles 26: GB3011, doi:10.1029/2012GB004375.

Burdige, D.J. 2007. Preservation of organic matter in marine sediments: controls, mechanisms, and an imbalance in sediment organic carbon budgets? Chemical Reviews 107: 467-485.

Clough, B. 1998. Mangrove forest productivity and biomass accumulation in Hinchinbrook Channel, Australia. Mangroves and Salt Marshes 2: 191-198.

Jennerjahn, T.C., Ittekkot, V. 2002. Relevance of mangroves for the production and deposition of organic matter along tropical continental margins. Naturwissenschaften 89: 23-30.

Posted 16 October 2015