珠江三角洲海陆交错带地下水营养盐系统输送与演变机理

Rapid urbanization in the Pearl River Delta and its impacts on marine/terrestrial eco-system are unique in terms of scale, magnitude and speed of urbanization processes. Based on the experimental station of Sun Yat-Sen University in Zhuhai campus, the proposed project intends to measure and analyze systematically the transportation flux of water and nutrients in marine-terrestrial interfaces from the recharge zone to the discharge zone and submarine groundwater discharge (SGD) as well by integrating physical-chemical, biological aspects and anthropogenic factors. Two catchments, one inside the campus and the other in Tangjia Town, standing for the natural background and the area of significant urbanization respectively are to be used for comparative study. Temporal changes and crucial processes and mechanisms regarding nutrients in the seawater/groundwater interface under the human activity effects are to be characterized, with an aim to identify the spatial and temporal patterns and possible evolution by using environmental isotopes，CFCs/SF6 and 16S rRNA as well. The results from the comparative studies of these two catchments are to be applied in the analyses of areal nutrient flux in the Pearl River Delta to reconstruct time series of nutrient change and its flux via SGD in the last 30 years. This sort of research is rare abroad and almost non-existent in China, and it could provide fundamental knowledge for the researches in global carbon/nitrogen cycle, environmental changes due to climate change and human activities, e.g. urbanization. This research could promote intersecting and integrating of multiple disciplines, and potentially be applied for municipal planning, environmental protection along the coastal line, marine fishery, offshore engineering, and exploitation and protective planning of groundwater. Three main subjects are given as: Systematic transportation of nutrients in the coastal seawater/groundwater (CSG) interface; Processes and mechanisms of nutrients in the CSG interface of two case-study catchments; Areal characteristics and flux of nutrients in the Pearl River Delta.

珠江三角洲城市化过程从其规模、速度及对海/陆生态环境的影响程度上无与伦比。以中山大学珠海试验基地为基础，综合微观的物理化学、微生物要素，从地下水补给区、排泄区直至入海，系统实测、分析海陆交错带中水与营养盐的输送过程，结合同位素特征，对比分析自然流域与邻近城镇化显著流域，研究人类活动影响下海水/地下水界面中的营养盐的迁移、转化机理。以此为基础，由点到面，分析珠江三角洲区域海岸带不同土地利用条件下地下水营养盐特征，重构近30年来营养盐变化的时间系列，估算营养盐入海通量及变化并分析成因。此类研究是全球规模城市化水环境效应、碳氮循环与生态环境变化等方面的基础，研究成果可促进学科交叉与融合，并服务于城市规划、沿海生态环境保护、海洋渔业、近岸工程、地下水开发利用与保护规划等。主要内容：海岸带海水/地下水营养盐输送系统及特征；海岸带海水/地下水营养盐演化机理；珠江三角洲地下水营养盐区域特征及通量估算。

以珠海唐家镇为中心，研究了从流域源头至海水的整个过程中营养盐的时空变化特征；同时采用了DPSIR（Driving force-Pressure-State-Impact-Response）框架解析海陆交互作用中的人文宏观要素，从宏观上探讨、分析珠江三角洲营养盐的时空差异及演变。通过沉积物定年，反演了石马河流域过去33年(1982-2014)营养盐的演变历史。通过四年的研究工作，积累了大量的基础数据，完成了26篇的研究论文（其中国际SCI刊物8篇，中国核心刊物18篇），指导毕业博士生2名，硕士生8名，这些指标超额完成了预期的研究成果。一些主要结果：1）在营养盐形态分布上，珠海市唐家镇区及东莞市塔岗村与南社古村地下水中氮营养盐均主要以NO3--N形式存在，磷营养盐以PO43-形态存在，NO3--N平均值为16.97 mg/L；PO43--P平均值为0.89 mg/L。枯水期地下水中NO3--N浓度较丰水期高；而PO43—P则相反。2) 利用16S rDNA基因测序对地下水中与氮循环有关的微生物及其丰度进行了确定，厌氧氨氧化细菌和反硝化甲烷氧化细菌沿补给区至排泄区均呈大幅增加的趋势，说明在中间区-排泄区存在脱氮过程。3）利用氮氧同位素技术并结合与氮有关的微生物分布特征发现：在珠海市唐家镇区，丰水期时地下水硝酸盐迁移转化主要受反硝化过程的影响；而枯水期则主要受混合作用的影响。4)珠海市琪澳岛单位海岸线长度海底地下淡水排泄量约为199 m3/d，计算了单位海岸线长度海底地下水营养盐的入海通量。唐家镇区通过地下水输送氮通量估算为1.99-4.70吨/年，约占该区域水体氮输出量的3.5-8.3%。5）石马河营养盐含量1991年以后呈现上升的趋势，这与1992年邓小平“南巡”讲话后的经济快速发展有关。上述研究及结论可为珠江三角洲/大湾区海陆交错带生态环境保护治理和生态文明建设提供科学依据。