利用^(15)N和^(18)O识别地下水硝酸盐污染源——以博茨瓦纳东南部拉莫茨瓦为例

Study on contamination sources of the nitrate in groundwater by nitrogen and oxygen isotopes in Ramotswa, Botswana

硝酸盐污染是博茨瓦纳地下水最严重的问题之一,严重影响了饮水安全。以博茨瓦纳东南部的拉莫茨瓦地区为例,采用水化学和同位素技术,对拉莫茨瓦地区12个地下水样品和2个地表水样品中的氨氮、硝酸盐和亚硝酸盐的含量和分布特征以及^(15)N和^(18)O同位素进行了分析,研究拉莫茨瓦地下水中的硝酸盐的来源和形成机理。结果表明拉莫茨瓦地下水以HCO_3-Mg型为主,硝酸盐含量较高的地下水主要来自于拉莫茨瓦白云岩含水层内,南部地下水中NO_3^-浓度小于北部地区。研究区的地下水主要来源与大气降水,北部地区蒸发作用较强。拉莫茨瓦村子地下水中的硝酸盐主要来源于粪便污染,受硝化与反硝化作用和蒸发作用的影响,墓地也对地下水中硝酸盐也存在一定影响。

Nitrate pollution is one of the most serious groundwater problems in Botswana, which is seriously affected the safety of drinking water. This study takes Ramotswa in southeastern Botswana as example, characteristics concentration and distribution of ammonia nitrogn, nitrate and nitrite, the source and mechanism of the nitrate in groundwater were studied on the basis of water chemical and isotopic geochemical. Water analysis of 14 groundwater and 2 surface water samples shows that the main water chemical type is HCO_3^-Mg, most samples with high concentration are from dolomiteaquifer in Ramotswa region, and nitrate in upstream is less than downstream and northern area. The groundwater in study area is mainly from the precipitation. Evaporation in the northern part is relatively intense. Isotope of^(15) N and^(18)O in nitrate indicates that the main source of nitrate in groundwater in Ramotswa village is feces, influence by nitrification, denitrification and evaporation. Graveyard is another important source of the nitrate in groundwater.