天津滨海地下水排放与营养盐输入研究

Over the last two decades,SGD is increasingly being recognized as an important factor in the understanding and sustainable management of coastal fresh aquifers and marine environment. SGD has been recognized to be a potentially significant source of freshwater and of nutrients and other dissolved chemical species to the coastal zone.The proposal choice the Tianjin coastal zone as research site,the research included fieldwork, laboratory experiments,and computer modeling.Quantifying SGD and associated nutrients from land aquifer by using hydrogeological survey and modeling.SGD flux will be estimated based on direct measurements by means of seepage meter, and its relations with driving forces and contributing factors like wave, tide, water depths will be explored. The magnitude of SGD along research site would be calculated by integrated using Ra isotopes.The water residence time will be determined using ratios of the short-lived radiotracer pair Ra-223 and Ra-224.We will use a mass balance model based on Ra-226 activities.to calculate the magnitude of SGD.SGD-driven nutrient fluxes are calculated by multiplying the average nutrient concentrations in groundwater with the SGD fluxes.Results were compared and complement with each other.This project has contributed to marine environmental management and the understanding of land/sea interactions by providing important estimates of SGD and associated nutrients fluxes to the sea.

近二十年来，海底地下水排泄（SGD）被认为是影响海岸带含水层和海洋环境的重要因素，对于滨海淡水和化学组份输入具有重要意义。本研究选择天津滨海带为研究场地，采用野外调查、实验室分析测试和数值模拟的方法开展SGD及其携带的营养盐研究。利用水文地质调查和数值模拟方法，查明陆地潜水向海洋的排放量。利用渗透计现场测量SGD，同时研究海水深度、波浪、潮汐等对SGD的影响。利用不同半衰期镭同位素集成使用的示踪方法，采用半衰期短的Ra-223、Ra-224确定水体滞留时间，利用半衰期长的Ra-226质量平衡方程计算SGD通量，以营养盐浓度与SGD通量关系计算营养盐通量。三种方法，相互补充，相互验证。研究成果提出渤海湾地下水排泄的证据及量值估计，为渤海环境管理提供科学依据。

地下水向海底的排泄过程，称为海底地下水排泄，是全球水文循环的重要环节，也是陆源地下水和溶解组分进入海洋的重要通道。地下水排泄是沿海环境生源要素、污染组分及淡水的重要“源”，对近岸水体初级生产力和生态环境具有重要意义。虽然科学界研究沿海地下水—地表水相互作用过程易经一个世纪，目前中国绝大多数沿海地区没有评估过海底地下水排泄对近岸水体的影响。本项目以高度工业化、人类工程活动特别是围海造陆活动剧烈的天津海岸带为研究场地，采用野外调查、镭同位素示踪和数值模拟相结合的方法，估算研究区海底地下水排及其携带的营养盐泄量值。通过本项目研究，取得以下研究成果：（1）首次证实了渤海湾SGD现象的存在并估算了其通量。（2）采用短半衰期镭同位素223/224估算得到了近岸海水滞留时间。（3）揭示了海岸带不同土地利用类型和人类工程活动（围海造陆）对SGD的影响作用。（4）采用数值模拟方法，研究了海岸带地下水—海水相互作用，揭示了海水入侵和海底地下水排泄交互存在的时空变化特征。（5）估算了地下水携带的氮磷营养盐通量。本文研究对于深化理解渤海湾化学组分平衡、修复水体富营养化、治理水体污染、保障受地下水影响的海水生态系统健康、改善水质管理方法选用具有基础科学意义。