渤海湾沉积地球化学记录及其对环境变迁的指示

Sedimentary geochemical records and their indications for environmental variations in Bohai Bay

为了解渤海湾营养环境的长周期变化特征及关键影响因素,于2018年4月和6月在渤海湾湾口外侧海域(BH47)及渤海湾湾口(BH15)采集沉积物柱状样,对沉积物柱状样中总有机碳(TOC)、总氮(TN)、磷(P)、生物硅(BSi)的含量以及碳、氮稳定同位素组成(δ^(13)C、δ15N)进行了分析,并结合气候和周围人类活动变化讨论以上参数的变化诱因。研究结果显示,两柱状样中TN含量自1980s起随时间呈现增加的变化趋势,与水体溶解无机氮(DIN)的长周期变化一致。污水排放、化肥施用和海水养殖是渤海湾氮的主要来源,其中农业化肥氮输入自2007年起有所下降,海水养殖和生活污水入海排放呈现持续上升的趋势。无机磷(IP)是沉积物中磷的主要存在形式,湾内的BH15柱中IP含量自1990s中期起呈现下降的趋势,湾口的BH47柱中IP含量呈现1970s后先减少,1990s起缓慢增加的变化趋势,两者均体现出明显的陆源输入特征。TOC/TN比值、δ^(13)C值以及δ^(13)C二端元混合模型对有机质来源的指示结果表明,渤海湾口及临近海域沉积物有机质受陆源输入和海洋自生共同影响,总体以海源有机质为主,自1990s起海源有机质贡献有所下降。与湾口的BH47柱相比,BH15柱更靠近近岸地区,受陆源输入的影响更显著,TN含量和陆源有机质贡献相对更高。本研究表明,为实现渤海湾水环境的有效治理,在对农业化肥的使用进行管制的同时,今后还需重点加强对海水养殖和生活污水入海排放的管控。

In order to understand the long-term variations in the nutritional environment and the key influencing factors of Bohai Bay,sediment cores from the mouth of the bay(BH15)and the outer area of the bay(BH47)were collected in April and June 2018 separately.The contents of total organic carbon(TOC),total nitrogen(TN),phos-phorus(P),biogenic silica(BSi),and stable isotopes of carbon and nitrogen(δ^(13)C,δ15N)were analyzed,and the causes of the changes of the above parameters were discussed in combination with the changes of climate and sur-rounding human activities.The results showed that the TN content in both sediment cores exhibited an increasing trend since the 1980s,which is consistent with the long-term variations in dissolved inorganic nitrogen(DIN)in the sea water.Sewage discharge,fertilizer application and mariculture are the main sources of nitrogen in the Bohai Bay,among which the input of agricultural fertilizer has decreased since 2007,while the discharge of mariculture and domestic sewage into the sea has shown a continuous upward trend.Inorganic Phosphorus(IP)was the main form of phosphorus in sediments.The IP in BH15 in the bay has shown a decreasing trend since the mid-1990s,while the IP in BH47 from the mouth of the bay has shown a decreasing trend after 1970s and a slow increasing trend since 1990s.All of them show obvious terrigenous input characteristics.The results of TOC/TN ratio、δ^(13)C value andδ^(13)C two-endmember mixing model indicated that the sediment organic matter in the mouth of Bohai Bay and adjacent sea area was influenced by both terrestrial input and marine autochthonous sources,with marine organ-ic matter being the dominant source,the contribution of marine organic matter has decreased Since the 1990s.Com-pared with the BH47 core from the mouth of the bay,the BH15 core is closer to the coastal area,more significantly affected by terrestrial input,with higher TN content and contribution of terrestrial organic matter.This study shows that in order to effectively manage the water environment of Bohai Bay,it is necessary to strengthen the control of mariculture and domestic sewage discharge into the sea while controlling the use of agricultural fertilizers in the fu-ture.