2010—2020年黄河下游河南典型灌区浅层地下水中砷和氟的演化 特征 及变化机制

Evolution Characteristics and Change Mechanism of Arsenic and Fluorine in Shallow Groundwater from a Typical Irrigation Area in the Lower Reaches of the Yellow River(Henan)in 2010—2020

黄河下游典型灌区河南段是豫北平原重要的农业种植区。该地区浅层水质整体较差,因常用于作物灌溉或家畜饮用,会对人体健康产生风险,因此对该地区地下水中砷与氟浓度变化特征和机制的研究将有助于提高对该地区地下水污染的认识水平。本文基于2010年和2020年在灌区范围内采集的327组浅层地下水样品,研究区内地下水砷和氟分布情况,并在此基础上对比研究十年间灌区浅层地下水中砷、氟的演化特征,探索分析砷与氟浓度及空间变化机制。研究结果表明:该地区浅层地下水中存在砷与氟超标问题,2020年浅层地下水中高砷(砷浓度大于10μg/L)和高氟(氟浓度大于1mg/L)的样品数量分别占总数的26.1%和26.06%。高砷水分布在太行山前洼地与黄河冲积平原等泥沙互层结构的沉积环境中,还原性较强,同时地下水径流不畅,较强的阳离子交换作用使得其所处环境中Ca^(2+)浓度较高。近十年间砷浓度增加的水样占总数31.8%,砷浓度减少的水样占36.7%。砷浓度的增长(减少)是地下水还原性增强(减弱)使得锰氧化物溶解释放(吸附)导致。近十年间不同地区农业灌溉和水源置换等用水方式导致水位变化是引起砷浓度变化的潜在因素。高氟水主要分布在河南新乡与濮阳的黄河沿线,氟离子浓度受到沉积物中萤石等钙质矿物溶解影响,使得高氟地下水出现在低钙环境中。近十年间研究区中氟离子浓度减少的占总数60.2%,氟离子浓度增加的占32.1%,整体变化趋势向好,但是高氟区中氟离子浓度继续增加。氟浓度的变化同样受到Ca^(2+)变化影响,在Ca^(2+)浓度降低(升高)时氟浓度进一步升高(降低)。地下水中氟升高地区分布在黄河沿线,因此受到黄河水补给影响较大,地下水径流条件较好,阳离子交换作用减弱,使得Ca^(2+)浓度降低,此时地下水中砷浓度受到环境影响而降低,因此研究区氟增加地区中砷与氟的分布和演化呈现反向关系。

BACKGROUND:A typical irrigation area of the downstream Yellow River(Henan)is an important agricultural planting area in the northern Henan Plain.The shallow water quality in this area is generally poor,which is often used for crop irrigation or livestock drinking,posing a risk to human health.Therefore,the study on the variation characteristics and mechanism of arsenic and fluorine content in groundwater in this area will help to improve the level of understanding of pollution in this area.OBJECTIVES:To investigate the spatial variation characteristics and mechanism of arsenic and fluorine concentration.METHODS:Based on 327 groups of shallow groundwater samples collected in 2010 and 2020 in the irrigated area,the distribution of arsenic and fluorine in the groundwater of the irrigated area was analyzed,and compared to the evolution characteristics of arsenic and fluorine in the shallow groundwater of the irrigated area in the last ten years.RESULTS:In 2020,the number of samples with high arsenic concentration(>10μg/L)and high fluorine concentration(>1mg/L)in shallow groundwater accounted for 26.1%and 26.06%,respectively.The high-arsenic groundwater was distributed in the sedimentary environments with interbedding structure of sediment,such as the Taihang Mountain depression and the Yellow River alluvial plain,with strong reducibility,poor groundwater runoff and strong cation exchange,resulting in high concentration of Ca^(2+)in the environment.Arsenic concentration increased in 31.8%of water samples and decreased in 36.7%of water samples in the last ten years.The increase of arsenic content was caused by the dissolution and release of manganese oxide due to the enhanced reducibility of groundwater.The variation of water level caused by agricultural irrigation and water replacement in different areas during the last ten years was a potential factor of arsenic concentration change.The high-fluorine groundwater was mainly distributed along the Yellow River in Xinxiang and Puyang,Henan Province.The concentration of fluorine ion was affected by the dissolution of calcareous minerals such as fluorite in the sediments,which made the high-fluorine groundwater appear in the low-calcium environment.In the last ten years,the study area with decreased fluorine ion concentration accounted for 60.2%,whereas areas with increased fluorine ion concentration accounted for 32.1%.The overall change trend was good,but the fluorine ion concentration in the high fluorine area continued to increase.Changes in fluorine concentration were also affected by changes in Ca^(2+),with further increases(decreases)as Ca^(2+)concentration decreased(increased).Elevated fluorine in groundwater was distributed along the Yellow River,affected greatly by the Yellow River water supply.So,the groundwater flow condition was good and the cation exchange was weakened,reducing the Ca^(2+)content.At this time,the arsenic content in the groundwater was less affected by the environment,so the study area with fluorine increase showed an inverse relationship between arsenic and fluorine in terms of regional distribution and evolution.CONCLUSIONS:This study will provide support for rational utilization of groundwater in the study area.