江汉平原中部浅层地下水中氨氮的有机质来源探究

江汉平原地下水氨氮浓度普遍超标，但是氮污染来源尚不明晰，尤其是对潜在的有机来源氮的认识还很不充分。本研究对江汉平原中部浅层地下水和沉积物中的溶解性有机质（Dissolved organic matter，DOM）荧光组分与氨氮关系进行了调查研究，并对沉积物的氮形态进行分析，探讨了沉积物中有机质向氨氮的潜在转化过程。研究表明研究区内浅层地下水中广泛分布溶解性有机碳与NH₄⁺，并且两者浓度呈现正相关关系（R²=0.42，p<0.01），该区域地下水呈现强还原环境有利于DOC与NH₄⁺的赋存。DOM荧光光谱谱图的平行因子分析（Parallel factor analysis，PARAFAC）结果表明：地下水与沉积物中DOM均含有类氨基酸与类富里酸组分。有机质组分荧光强度与氨氮浓度相关性结果表明：沉积物DOM中类富里酸和类氨基酸组分与氨氮均呈现强正相关性（R²=0.92~0.96，p<0.01）；地下水中DOM类富里酸组分与氨氮呈现较强的正相关性（R²=0.62~0.66，p<0.01），而类氨基酸组分与氨氮的正相关性不明显。地下水中相较沉积物中，DOM的类富里酸和类氨基酸组分与氨氮相关性减弱，这种变化可能指示了类富里酸稳定赋存在含水层，而类氨基酸更容易分解消耗。沉积物中凯氏氮占总氮的87.04%~93.51%，表明沉积物中的氮主要为可以转变为NH₄⁺的有机氮形态，因而满足了地下水中的NH₄⁺由沉积物有机氮转化产生的必备条件。江汉平原沉积物中有机氮的分解是浅层地下水氨氮的重要来源。

Investigation on the Organic Matter Source of Ammonia Nitrogen in Shallow Groundwater of the Central Jianghan Plain

The concentrations of ammonia nitrogen (AN) in most groundwater samples collected from the Jianghan Plain were above the limit in the drinking water standard. However, knowledge on the source of AN was relatively deficient, especially the organic matter source. In this study, the relationships between fluorescence components of dissolved organic matter (DOM) and ammonia nitrogen in shallow groundwater and sediment samples from the Central Jianghan Plain were investigated, the nitrogen species in sediment samples were analyzed, and the potential transformation process of from organic matter to AN in sediments was discussed. This study showed that dissolved organic carbon (DOC) and NH₄⁺ distributed widely in the shallow groundwater with a positive correlation between them (R²=0.42, p<0.01). The strong reducing environment of groundwater is favorable to the occurrence of DOC and NH₄⁺. Parallel factor analysis (PARAFAC) of DOM fluorescence spectra showed that DOM in groundwater and sediments contained fulvic acid-like and amino acid-like components. A strong positive correlation existed between total fulvic acid-like and amino acid-like components and AN in sediment samples (R²=0.92-0.96, p<0.01). The correlation between fulvic acid-like components and AN in groundwater was positive and strong (R²=0.62-0.66, p<0.01), whereas the positive correlation between amino acid-like components and AN was relatively weak, implying that fulvic acid-like components might be more stable while amino acid-like components might be more easily decomposed and consumed in the aquifer. Kjeldahl nitrogen accounts for 87.04%-93.51% of total nitrogen in sediments, indicating that the organic nitrogen, which could be transformed into NH₄⁺, was the main form of nitrogen in sediments. Therefore, we concluded that decomposition of organic nitrogen in sediments was the important source of AN in the shallow groundwater of the Jianghan Plain.