Zidan Alyaa A, Wu Zijun, Wang Yiqing, Chen Yuanqing, Liu Jiawei
State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China; National Institute of Oceanography and Fisheries, NIOF, Cairo, Egypt.
State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China.
Mar Pollut Bull. 2025 Mar;212:117575. doi: 10.1016/j.marpolbul.2025.117575. Epub 2025 Jan 16.
Investigations of the spatial-temporal variations of nutrients within mangrove coastal zones are essential for assessing the environmental status of an aquatic ecosystems. However, major processes controlling nitrate cycle along the submarine groundwater discharge (SGD) pathway from the mangrove areas to adjacent tidal creek remain underexplored. A time series measurement over a 25 h tidal cycle was conducted in Qinglan Bay tidal creek (Hainan Island, China). Samples of the creek seawater, nearby terrestrial groundwater and sediment porewater were collected for analysis of nutrient concentrations and dual nitrate isotopic compositions (δN-NO and δO-NO). We observed high concentrations of nutrients in terrestrial groundwater, and their concentrations decreased with distance towards the coastal area. Using dual nitrate isotopes and a MixSIAR model, we concluded that ammonia nitrogen fertilizer (Amm-NF) is the primary nitrate sources for groundwater, while creek water nitrate originates from various sources, including manure and sewage, soil organic nitrogen, and chemical fertilizer. The isotopic ratios (δO: δN) suggest active nitrification occurs in low tide creek water, whereas assimilation and limited denitrification occurs in high tide creek water and groundwater. Based on previous report of SGD rate in the region, we calculated the flux of SGD-derived nutrient export to coastal water, and the result indicates low N: P ratio and N limitation in the tidal creek. This study highlights the complexity of different sources and biogeochemical processes that impact the nutrient distribution and nitrate dynamics in the nearshore mangrove ecosystem. Understanding these processes is essential for effectively protecting and managing of the mangrove aquatic ecosystem.
研究红树林海岸带营养物质的时空变化对于评估水生生态系统的环境状况至关重要。然而，从红树林区域到相邻潮汐小溪的海底地下水排放（SGD）路径上控制硝酸盐循环的主要过程仍未得到充分探索。在中国海南岛的清澜湾潮汐小溪进行了为期25小时潮汐周期的时间序列测量。采集了小溪海水、附近陆地地下水和沉积物孔隙水样本，用于分析营养物质浓度和双硝酸盐同位素组成（δN-NO和δO-NO）。我们观察到陆地地下水中营养物质浓度很高，且其浓度随着向沿海地区的距离增加而降低。利用双硝酸盐同位素和MixSIAR模型，我们得出结论，氨氮肥（Amm-NF）是地下水硝酸盐的主要来源，而小溪水硝酸盐则来自多种来源，包括粪便和污水、土壤有机氮和化肥。同位素比率（δO:δN）表明，退潮时小溪水中发生活跃的硝化作用，而涨潮时小溪水和地下水中发生同化作用和有限的反硝化作用。根据该地区先前关于SGD速率的报告，我们计算了SGD来源的营养物质向沿海水体输出的通量，结果表明潮汐小溪中氮磷比低且存在氮限制。本研究突出了影响近岸红树林生态系统营养物质分布和硝酸盐动态的不同来源和生物地球化学过程的复杂性。了解这些过程对于有效保护和管理红树林水生生态系统至关重要。
