长江中游沿岸地下水中铵氮与磷的共存规律及其控制因素

长江中游平原区面临着一系列严重的地质环境问题,其中地下水铵氮和磷的问题十分突出,但目前对于二者共存规律的认识还十分薄弱。以长江中游沿岸故道区为典型研究区,对采集的地下水样品进行了水文地球化学分析,并综合运用因子分析和随机森林模型探讨了铵氮和磷的赋存规律。结果表明:地下水整体处于还原环境中,NH₄-N的质量浓度为0.03~71.0 mg/L(均值9.92 mg/L),P的质量浓度为0.02~3.38 mg/L(均值0.51 mg/L)。地下水中高浓度的铵氮与磷均主要为天然成因,但铵氮与磷的迁移富集过程存在差异:铵氮的迁移富集与含氮有机质矿化过程密切相关;磷的迁移富集与铁氧化物或氢氧化物的还原性溶解密切相关,而含磷有机质矿化是磷富集的次要过程。Eh很低的地下水环境易产生高浓度铵氮的地下水,相对中等的还原环境会产生高浓度的磷但通常不会伴生高浓度的铵氮;当地下水中S^2-,DOC,I均处于相对较高的浓度水平时会伴生大量的铵氮,而磷的浓度在很大程度上受控于Fe²⁺浓度;当DOC,I和Fe²⁺浓度都高时,通常会出现铵氮和磷浓度都较高的现象。

Coexistence and controlling factors of ammonium and phosphorus in groundwater along the middle reaches of the Yangtze River

The plain area of the middle reaches of the Yangtze River is faced with a series of serious geological environment problems, among which the groundwater ammonium and phosphorus are the most abnormal, but the understanding of their coexistence is still very weak.In this paper, the hydrogeochemical analysis was carried out on the groundwater samples collected from the oxbows along the middle reaches of the Yangtze River, and the occurrence rules of ammonium and phosphorus were discussed by means of factor analysis and random forest model.The results showed that: Groundwater is in reductive environment as a whole, the mass concentration of NH₄-N is 0.03-71.0 mg/L(the mean is 9.92 mg/L), and the mass concentration of P is 0.02-3.38 mg/L(the mean is 0.51 mg/L).High concentration of ammonium and phosphorus in groundwater are mainly from natural causes.However, the migration and enrichment processes of ammonium and phosphorus are different.The migration and enrichment of ammonium is closely related to the mineralization process of organic matter.The migration and enrichment of phosphorus is closely related to the reductive dissolution of iron oxide/hydroxide, and the mineralization of organic matter containing phosphorus is the secondary process of phosphorus enrichment.A low Eh groundwater environment is prone to produce high ammonium groundwater, while a relatively medium reduction environment will produce high phosphorus but usually not associated with high ammonium nitrogen.When S2-, DOC and I are in relatively high concentrations, a large amount of ammonium is associated, while the concentration of phosphorus is largely controlled by the concentration of Fe2+.When DOC, I, and Fe2+ are all high, high concentrations of ammonium and phosphorus are usually present.