广西北部湾近岸海域营养盐与富营养化状态研究

Nutrient and Eutrophication in Coastal Waters of Beibu Gulf in Guangxi

关键词:  营养盐  富营养化  营养盐浓度  营养盐结构  近岸海域

Key words:  nutrients  eutrophication  nutrient concentration  nutrient structure  nearshore waters

摘要:

为全面了解广西北部湾近岸海域营养盐与富营养化程度，于2021年8月和2022年1月在珍珠湾、钦州湾、廉州湾、铁山港和涠洲岛海域共27个站位采集表层水，分析营养盐浓度，并运用营养盐限制因素评价方法和富营养化指数法分析营养盐结构特征和富营养化状况。结果表明：广西北部湾近岸海域夏季表层水体溶解态无机氮（DIN）、磷酸盐（PO₄^3--P）和硅酸盐（SiO₃^2--Si）均值分别为0.177 mg/L、0.019 mg/L和0.578 mg/L，冬季三者分别为0.162 mg/L、0.021 mg/L和0.324 mg/L，营养盐浓度均为SiO₃^2--Si>DIN>PO₄^3--P；其中DIN和SiO₃^2--Si平均值在夏季高于冬季，而PO₄^3--P为夏季略低于冬季。各海湾营养盐浓度大小依次为铁山港和钦州湾>廉州湾>珍珠湾>涠洲岛，且在4个海湾均呈湾内向湾外递减的空间变化趋势。夏季氮磷摩尔比（N/P）、硅氮摩尔比（Si/N）和硅磷摩尔比（Si/P）分别为4.3-35.2，0.5-6.5和12.0-139.9，对应均值分别为19.6，2.0和35.5，以潜在磷（P）限制为主，占所有站位的29.6%；氮（N）限制占14.8%，其余站位无营养盐限制的情况。冬季N/P、Si/N和Si/P分别为4.3-36.2，0.8-2.0和8.4-37.1，对应均值分别为20.4，1.1和21.5，以潜在P限制为主，占所有站位的36.4%；N限制占9.1%。夏季富营养化指数E为0.04-3.92，平均值为1.13；冬季富营养化指数E为0.03-3.68，平均值为1.08，夏季富营养化程度略高于冬季。总的来说，北部湾近岸铁山港富营养化程度最高，其次为钦州湾，两者绝大部分海域均已达到中度富营养，廉州湾30.0%海域达到轻度富营养，而珍珠湾和涠洲岛均属于贫营养。本研究结果可为北部湾海洋环境保护和海水养殖提供基础数据。

Abstract:

In order to comprehensively understand the nutrient and eutrophication in coastal waters of Beibu Gulf in Guangxi, surface waters were collected from 27 stations in Zhenzhu Bay, Qinzhou Bay, Lianzhou Bay, Tieshan Bay and Weizhou Island in August 2021 and January 2022. The nutrient concentrations were analyzed, and the structure characteristics and eutrophication status of nutrients were analyzed by nutrient limiting factor evaluation method and eutrophication index method. The result showed that the average values of inorganic nitrogen (DIN), phosphate (PO₄^3--P), and silicate (SiO₃^2--Si) in surface waters of the coastal waters of Beibu Gulf in summer was 0.177 mg/L, 0.019 mg/L and 0.578 mg/L, respectively, and in winter which was 0.162 mg/L, 0.021 mg/L and 0.324 mg/L, respectively. Nutrient concentrations were (SiO₃^2--Si)>DIN>PO₄^3--P. The average values of DIN and SiO₃^2--Si were higher in summer than that in winter, while PO₄^3--P was slightly lower in summer than that in winter. The nutrient salt concentrations were in the order of Tieshan Bay and Qinzhou Bay>Lianzhou Bay>Zhenzhu Bay>Weizhou Island, and showed a spatial variation trend of decreasing from inside to outside in all four bays. In summer, the ratio of N/P, Si/N, and Si/P was 4.3-35.2, 0.5-6.5 and 12.0-139.9, and the corresponding mean values was 19.6, 2.0 and 35.5, respectively. Phosphate was the main potential limitation, accounting for 29.6% of all stations, while nitrogen limitation accounted for 14.8%, and there was no nutrient limitation at other stations. In winter, the ratio of N/P, Si/N and Si/P was 4.3-36.2, 0.8-2.0 and 8.4-37.1, and the corresponding mean values was 20.4, 1.1 and 21.5, respectively. Phosphate was the main potential limitation, accounting for 36.4% of all stations. N limitation accounted for 9.1%.The eutrophication index E in summer was 0.04-3.92, and the average value was 1.13.The eutrophication index E in winter was 0.03-3.68, and the average value was 1.08.The degree of eutrophication in summer was slightly higher than that in winter. In general, the eutrophication degree in coastal waters of Beibu Gulf Tieshan Bay is the highest, followed by Qinzhou Bay, both of which have reached moderate eutrophication, and 30.0% of the waters of Lianzhou Bay have reached mild eutrophication, while Zhenzhu Bay and Weizhou Island are both at a poor eutrophication.The results of this study can provide basic data for marine environmental protection and mariculture in Beibu Gulf.