1115 / 2019-07-24 15:51:22

Impacts of Southeast Asia economic boom on coral reefs - A case study from Taiwan

6、海洋地球科学 > 专题1：珊瑚对多尺度气候变化的记录与响应

Excessive sedimentation transported into coastal seawater induced by human activities has profound detrimental effects on coral reefs. Southeast Asia, possess the highest coral biodiversity on the planet, has undergone rapid economic boom in the past decades which transported amounts of sedimentation into coastal seawater and putted great pressures onto coral reef resources. However, due to the lack of long and continuous records, we cannot evaluate of sedimentation threats on coral reefs now and the status of coral reefs in the near future. Here we present monthly-resolved records of Ba/Ca ratios and δ137/134Ba from the Nanwan coral (NW) in the coastal region of southern Taiwan to establish its response to economic boom since 1980s. This study shows that the coral Ba/Ca baseline increased about 50% during 1987-1996 (3-4 μmol/mol, Period II) compared to 1980-1986 (2-2.5 μmol/mol, Period I). And the Ba/Ca peaks in Period II are abnormally high (5-6 μmol/mol), enrichment up to 100% than Period I and Period III (1997-2004) (2-3.5 μmol/mol). Considering both of terrestrial runoff and upwelled water are enriched in Ba, the primary factor for the increased NW coral Ba/Ca event remains difficult to interpret merely based on Ba/Ca proxy. Stable Ba isotopic analyses can help address these issues as Ba-isotopic compositions of terrestrial runoff and upwelled water are totally different. In addition, δ137/134Ba values of surface and upwelled water have significance differences. The fact of a narrow range of δ137/134Ba proxy (0.24 ± 0.03‰ to 0.30 ± 0.03‰) with the elevated coral Ba/Ca ratio suggests that upwelling is not the driving force for enriching NW coral Ba. Terrestrial Ba input induced by land-based activities accompanied by economic development, with higher Ba concentration and lighter and homogenous δ137/134Ba values than surface water, are likely the primary source for Ba enrichment. In addition, owing to economic boom of Southeast Asia, the increase of land-based terrestrial input has also been documented by corals trace elements in South China and Vietnam. Coral Ba/Ca and Ba isotopes could be used for tracing land-based activities and provide a rigorous scientific background for policy formulation, which in support of protecting these vital nature resources under anthropogenic disturbance.