Abnormally High Ammonium of Natural Origin in a Coastal Aquifer-Aquitard System in the Pearl River Delta, China
Abnormally High Ammonium of Natural Origin in a Coastal Aquifer-Aquitard System in the Pearl River Delta, China
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DOI：
10.1021/es1021697
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发表时间：
2010-10-01
影响因子：
11.4
通讯作者：
Wen, Dongguang
中科院分区：
文献类型：
--
作者：
Jiao, Jiu Jimmy;Wang, Ya;Wen, Dongguang
河流和含水层系统的高氮含量是一个重大关切，因为它可能对人类健康和水质产生影响，如湖泊和沿海地区的富营养化。这种氮富集通常归因于人为来源，如污水和农业及工业废物。研究目的是揭示珠江三角洲（PRD）滨海含水层系统地下水铵态氮的空间分布特征，并探讨异常高铵态氮的成因。共钻了40个井眼，以收集弱透水层的岩心样品和基底含水层的地下水样品。岩心样品用于提取孔隙水，用于离心和室内批量化学分析。与以往的研究主要集中在含水层，本研究处理含水层弱透水层系统作为一个水文地球化学连续体。结果表明，含水层-弱透水层系统中铵态氮的总量异常大。在20-50米深的基底砂更新世含水层中，铵的浓度高达390毫克/升，是全球地下水报告的最高浓度。这种铵是天然的，面积广泛（1600 km（2）），起源于上覆的全新世-更新世弱透水层，并通过地下水迁移和扩散进入含水层。含水层中的总铵（190 x 10（6）公斤）比弱透水层中的总铵（8 600 x 10（6）公斤）高出45倍。许多有机氮残留在弱透水层中，可转化为铵。这些含水层中的天然铵被缓慢地输送到珠江三角洲河道和南海河口。通过在河道和河口挖砂，这一贡献率可能会大大增加。尽管珠三角地下水中的铵是全球报告的最大浓度和质量，但文献显示没有其他三角洲弱透水层的报告，因此在富含有机物的弱透水层中形成的丰富铵可能并不罕见，这种“地质”铵源可能是迄今为止未被认识到的大量氮排放到地表沃茨的来源。
High-nitrogen loadings of rivers and aquifers systems are a major concern because of potential effects on human health and water quality impacts such as eutrophication of lakes and coastal zones. This nitrogen enrichment is commonly attributed to anthropogenic sources such as sewage and agricultural and industrial wastes. The aims of this study were to delineate spatial distribution of groundwater ammonium in the coastal aquifer system in Pearl River Delta (PRD), China and to identify the origin of the abnormally high ammonium. A total of 40 boreholes were drilled to collect core samples of the aquitard and groundwater samples in the basal aquifer. The core samples were used for extraction of pore water for centrifugation and bulk chemical analyses in laboratory. Unlike previous studies which focused mainly on the aquifer, this study treated the aquifer-aquitard system as a hydrogeochemical continuum. The results show that the aquifer-aquitard system contains an exceptionally large total ammonium mass. Ammonium occurred at concentrations up to 390 mg/L in the basal sand Pleistocene aquifer 20-50 m deep, the largest concentration reported for groundwater globally. This ammonium was natural, areally extensive (1600 km(2)) and originated in the overlying Holocene-Pleistocene aquitard and entered the aquifer by groundwater transport and diffusion. Total ammonium in the aquifer (190 x 10(6) kg) was exceeded by total ammonium in the aquitard (8600 x 10(6) kg) by a factor of 45. Much organic nitrogen remained in the aquitard available for conversion to ammonium. This natural ammonium in the aquifer was slowly transported into the PRD river channels and the estuary of the South China Sea. The rate of this contribution will likely be greatly increased by sand dredging in the river channels and estuary. Although the ammonium in PRD groundwater occurred in the largest concentrations and mass reported globally, the literature shows no reports of other delta aquitards having been examined for ammonium occurrence and therefore abundant ammonium formed in aquitards rich in organic matter may not be uncommon and this "geologic" source of ammonium may present a large and hitherto unappreciated source of nitrogen discharging to surface waters.