College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China.
Marine Environmental Monitoring Centre of Beihai, State Oceanic Administration, Beihai 536000, China.
Int J Environ Res Public Health. 2020 Mar 16;17(6):1921. doi: 10.3390/ijerph17061921.
Nitrate (NO) dual isotope analysis was performed in Zhanjiang Bay, which is a closed bay with intensive human activities in South China, to investigate seasonal changes in the main NO sources and their biogeochemical processes in the monsoon-controlled climate. The relatively low N/P ratios in Zhanjiang Bay suggests that nitrogen (N) is a limiting nutrient, which indicates that the increase of N is favorable for phytoplankton proliferation. However, a sufficient amount of ammonium was found in our study area owing to intensive human activities, which can support biological processes. Thus, less NO biological processes were found, indicating that NO isotopic characteristics may reveal details of the mixing from various sources. The Bayesian mixing model showed that NO in the upper bay originated from manure (43%), soil N (30%), N fertilizer (17%), and N precipitation (10%) during winter, which reflects the local human activities; while NO sources during summer were mainly N fertilizer (36%), soil N (32%), and manure (31%), indicating the source as the runoff from the upper river basin. Our results suggest that nitrate dual-isotope was very useful for tracing the main NO sources in the condition of the sufficient ammonium, and runoff exerted an important impact on the shift in NO sources between both the local source and the source from the upper river basin during the two seasons in this monsoon-controlled bay.
在中国南方受人类活动强烈影响的封闭性港湾——湛江湾进行硝酸盐（NO）双同位素分析，以研究季风控制气候下主要 NO 源的季节变化及其生物地球化学过程。湛江湾相对较低的 N/P 比值表明氮（N）是一种限制营养物，这表明 N 的增加有利于浮游植物的增殖。然而，由于人类活动的强烈影响，在我们的研究区域发现了大量的铵，这可以支持生物过程。因此，发现的生物 NO 过程较少，这表明 NO 同位素特征可能揭示了各种来源混合的细节。贝叶斯混合模型表明，冬季上湾的 NO 主要来源于粪肥（43%）、土壤 N（30%）、N 肥料（17%）和 N 降水（10%），反映了当地的人类活动；而夏季的 NO 源主要是 N 肥料（36%）、土壤 N（32%）和粪肥（31%），表明来源是上游流域的径流水。我们的研究结果表明，在有足够铵的情况下，硝酸盐双同位素对于追踪主要 NO 源非常有用，而径流水在季风控制的港湾这两个季节中对 NO 源从当地源到上游流域源的转变产生了重要影响。
