珠江口近岸海域无机氮的来源与输送途径研究

The offshore area near the Pearl River Estuary (PRE) is next to the distribution area of the quaternary aquifer containing abnormally high ammonium groundwater, and also within the influence area of the Pearl River plum, therefore, inorganic nitrogen of the seawater in this area from both natural processes and anthropogenic activities are significant. This study chooses the offshore area near the PRE as the study area. Radium and radon isotopes, inorganic nitrogen isotopes as well as water chemical studies are going to be carried out to understand the spatial and temporal variations of submarine groundwater discharge (SGD), to estimate the amounts of SGD, as well as the amounts of inorganic nitrogen transported by both SGD and river runoff. Stable inorganic nitrogen isotopic analysis would be adopted to separate natural and anthropogenic inorganic nitrogen in the river runoff. Based on the above analyses, inorganic nitrogen budgets of the offshore ecosystem would be carried out, both natural and anthropogenic factors regarding high inorganic nitrogen loadings of seawater in the study area will be individually identified, significant inorganic nitrogen contributions from the discharge of abnormally high ammonium groundwater of natural origin will be estimated, and the role of each pathway for nitrogen transportation will be evaluated, especially their roles in terms of natural nitrogen recycling. This study is the basis of the studies of global nitrogen recycling and ecological environment change. The findings can be good references for understanding the occurrences and pathways of inorganic nitrogen in other offshore areas where have inorganic nitrogen pollution problems, and can also be helpful for marine fishery, as well as ecological environment protection and groundwater development and protection in the coastal zones.

珠江口近岸海域紧邻三角洲天然高铵含水层分布区，又在珠江水系显著影响范围内，无机氮污染的自然与人为影响都十分显著。但该区域现有无机氮污染研究理解不够全面，特别对自然因素认识不足。本项目采用放射性镭和氡同位素技术，无机氮稳定同位素技术，辅以水质分析等方法，解析研究海域海底地下水排放（SGD）的空间特征，揭示SGD随季节和涨落潮周期的变化规律，估算SGD及河流对天然和人为无机氮分别的输送量。在此基础上，结合研究海域无机氮输入、输出平衡计算，全面、准确地阐释珠江口近岸海域高无机氮污染产生的根本原因，揭示自然因素对河口近岸海域无机氮污染的贡献，辨明SGD和河流等途径分别在海、陆间天然氮循环中所起的作用。本项目是全球氮循环与生态环境变化等研究的基础，研究成果既能为理解与应对世界其他河口海岸带类似的无机氮污染问题，提供科学方法和依据，并可服务于海洋渔业、海岸带生态环境保护和地下水开发利用与保护等。

珠江口近岸海域紧邻三角洲天然高铵含水层分布区，又在珠江水系显著影响范围内，无机氮污染的自然与人为影响都十分显著。人们对该区域现有无机氮污染研究理解不够全面，特别是对自然因素认识不足。本项目采用放射性镭和氡同位素技术，无机氮稳定同位素技术，辅以水质分析等方法，解析研究海域海底地下水排放(SGD)的空间特征，揭示SGD随季节和涨落潮周期的变化规律，估算SGD及河流对天然和人为无机氮分别的输送量。研究初步揭示，珠江河口及近岸海域总的SGD高达(1.6-2.5) ×108 m3/d（0.015-0.023 m3/m2·d），占珠江同期平均流量的（8-13）%；该区SGD来源以陆源为主，陆源SGD占总SGD的72.4%，即为(1.2-1.8) ×109 m3/d（0.011-0.017 m3/m2·d），为珠江的同期平均流量（6-9）%；珠江三角洲地区第四纪天然高铵地下水随着SGD排泄入海，无机氮输入量可达(4.3-6.6)×106 kg/d，高于珠江同期的无机氮输入量3.8×106 kg/d。上述研究结果在进一步验证和修正中。此外，研究还揭示，天然高铵地下水的排放引发了相应海域的溶解氧降低，对夏季低氧区发育具有重要的贡献作用；同时，受影响海域还出现了海水氧化还原电位及pH值降低等显著的水环境效应。本项目目前发表论文共计5篇，其中SCI论文3篇，中文核心期刊论文2篇，另有两篇研究论文在修改完善准备投递中。本研究是全球氮循环与生态环境变化等研究的基础，研究成果既能为理解与应对世界其他河口海岸带类似的无机氮污染问题，提供科学方法和依据，并可服务于海洋渔业、海岸带生态环境保护和地下水开发利用与保护等。 也可为珠江口海水污染管控与治理、海水区域功能规划，粤港澳大湾区的生态环境保护与发展规划等提供科学依据。