对珠江口外和粤西沿海的两个具百余年沉积历史的柱状样进行了基于支链与 类 戊二烯甘油 四醚 (glycerol dialkyl glycerol tetraether , GDGT) 化合物比值的 BIT( branched and isoprenoid tetraether ) 指标分析 , 该指标指示的是沉积有机质中陆源土壤来源有机质的相对输入贡献。结果发现 , BIT 值在两个柱状样中都小于 0.26, 显示水生有机质是沉积有机质的主要来源。 BIT 时间序列在两个柱状样中表现出一致的变化趋势 : 大约在 1940 年代以前 , BIT 保持在相对稳定的高值 , 此后表现出逐渐下降趋势 , 1990 年以来下降趋势显著。这一下降趋势表明 , 半个多世纪以来沉积有机质中陆源有机质的相对贡献是持续减少的 , 或者水生有机质的相对贡献是持续增加的。在分析了陆源和水生有机碳沉积通量变化序列的基础上 , 认为水生生产力对沉积有机质的相对贡献持续增大是 BIT 指数持续降低的主要原因。水生有机碳输出通量半个多世纪来的上升趋势及其与广东省 GDP 变化趋势的相似性表明 , 陆地人类活动的不断增强导致了沿海水域营养化水平的不断升高。
Two sediment cores, covering histories of ca. one hundred years and located in coastal waters off Guangdong province, were analyzed for branched and isoprenoid tetraether (BIT) index based on glycerol dialkyl glycerol tetraether (GDGT) biomarkers. The index is an indicator of relative contribution of terrestrial soil organic carbon (SOC) to the total organic carbon (TOC) in the sediment. Our results revealed that BIT values were lower than 0.26 in the core sediments, indicating major contributions of aquatic organic carbon (AOC) to the TOC. BIT time series from the two cores showed similar patterns with stable and higher values before the 1940s, a gradual decreasing trend after the 1940s and a prominent decreasing trend since 1990. The decreasing trend suggests either a decrease in SOC or an increase in AOC. Based on the time series of the sedimentation flux of SOC and AOC, increasing contribution of AOC was inferred to be the main cause. The increasing sedimentation flux of AOC showed a similar pattern to that of the economic rise in Guangdong province, implying that the suggested rise of nutrient levels of coastal waters off Guangdong province could have been caused by the enhanced human activities.
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