Yang Zhi, Chen Jianfang, Xu Xiaoqun, Ran Lihua, Jin Haiyan, Wang Bin, Chen Qianna
Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China; State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China.
Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China.
Mar Pollut Bull. 2025 Mar;212:117535. doi: 10.1016/j.marpolbul.2025.117535. Epub 2025 Jan 9.
Xiangshan Bay, one of China's most eutrophic semi-enclosed bays, was studied to examine the seasonal distributions of salinity, temperature, nutrients, and nitrate isotopes (δN and δO) to elucidate seasonal variations in nitrate sources and the key factors driving nitrogen level fluctuations. Based on nitrate δN (6.1-8.9 ‰) and δO (0-5.7 ‰) values, the primary nitrogen sources in Xiangshan Bay were identified as domestic sewage and agricultural runoff, influenced by seasonal agricultural activities and monsoon-driven Changjiang Diluted Water (CDW) dynamics. Nitrate levels peaked in autumn (53.1 ± 1.6 μmol/L), due to intensive agricultural activity and strong CDW intrusion driven by the northeast monsoon. Conversely, the southwest monsoon in summer, coupled with higher nitrogen uptake due to warmer temperatures and increased light availability, resulted in the lowest nitrate levels (35.2 ± 5.4 μmol/L). In winter, reduced nitrate inputs were observed, reflecting minimal agricultural activity and weaker Changjiang discharge. Differences in nitrate levels between the upper and lower bay were attributed to weaker mixing and stronger local inputs in the upper bay.
象山湾是中国富营养化最严重的半封闭海湾之一，本研究对其盐度、温度、营养物质和硝酸盐同位素（δN和δO）的季节分布进行了调查，以阐明硝酸盐来源的季节变化以及驱动氮水平波动的关键因素。根据硝酸盐δN（6.1 - 8.9‰）和δO（0 - 5.7‰）值，确定象山湾的主要氮源为生活污水和农业径流，这受到季节性农业活动以及季风驱动的长江冲淡水（CDW）动态变化的影响。硝酸盐水平在秋季达到峰值（53.1 ± 1.6 μmol/L），这是由于农业活动密集以及东北季风驱动的强烈长江冲淡水入侵所致。相反，夏季的西南季风，加上温度升高和光照增加导致的更高氮吸收，使得硝酸盐水平降至最低（35.2 ± 5.4 μmol/L）。在冬季，观察到硝酸盐输入减少，这反映出农业活动最少且长江径流量较弱。湾上部和下部硝酸盐水平的差异归因于上部湾混合较弱和局部输入较强。
