密云水库流域地下水硝态氮的分布及其影响因素

2008年11月至12月,采集了密云水库流域305个井的地下水样品,分析了其硝态氮含量。结果表明,密云水库流域地下水的硝态氮含量的平均值、超标率(10 mg L-1≤NO3--N<20 mg L-1)和严重超标率(NO3--N≥20 mg L-1)分别为6.81 mg L-1、13.77%和2.30%。其中村庄和菜地的地下水硝酸盐污染最为严重,35个村庄井和13个菜地井的地下水硝态氮含量的平均值分别为9.52 mg L-1和9.55 mg L-1,已接近WHO饮用水硝态氮含量10 mg L-1的限定标准,超标率分别为20%和15.38%,严重超标率分别为8.57%和7.69%。219个粮田井水的硝态氮水平位居中间,其硝态氮含量的平均值、超标率和严重超标率分别为6.59mg L-1、14.61%和1.37%。10个林地井的地下水硝态氮含量是最低的,其平均值为2.66 mg L-1,无超标现象。潮河流域农田地下水的硝酸盐污染比白河流域严重。潮河流域农田(124个井)的地下水硝态氮含量的平均值、超标率和严重超标率分别为8.42 mg L-1、21.77%和3.23%,而白河流域(122个井)则分别为5.03mg L-1、6.56%和0,即无严重超标现象。密云水库流域农田地下水的硝态氮含量呈现出上游低而下游高的趋势。玉米田地下水硝态氮含量在接近河道的地方有所降低,与地下水水位呈负相关,与化肥氮的施用量呈正相关,当地下水位小于7m时或当一年的化肥氮的施用量超过200 kg hm-2,存在地下水硝态氮含量超标的潜在危险。

Nitrate concentrations in groundwater of Miyun Reservoir watershed

305 groundwater samples from wells in Miyun Reservoir watershed were collected from November to December, 2008, and nitrate nitrogen (NO3--N) concentrations in groundwater were tested. Average NO3--N concentration for all wells sampled was 6.81mg/L, and 16.07% of all wells exceeded 10mg/L, the WHO limit for NO3--N in drinking water. Among them, 35 wells from villages and 13 wells from vegetable lands show high NO3--N concentrations with averages of 9.52 mg/L and 9.55mg/L respectively, near the WHO limit. 28.57% of village wells and 23.07% of vegetable land wells respectively exceeded the WHO limit. 219 wells from croplands (corn and soybean) presented the middle NO3--N concentrations with average of 6.59mg/L and of which 16.08% were above the WHO limit. 10 wells from woodlands demonstrated low NO3--N concentrations with average of 2.66mg/L and none of them were beyond the WHO limit. Nitrate pollution of groundwater in Chaohe River basin was more severe than that in Baihe River basin. Average NO3--N concentration in groundwater from farmlands in Chaohe River basin reached 8.42mg/L, which was higher than that (5.03mg/L) in Baihe River basin. 25% of 124 wells from farmlands exceeded the WHO limit in Chaohe River basin while only 6.56% of 122 wells did in Baihe River basin. High nitrate concentrations in groundwater resulted from more intensive agriculture in Chaohe River basin. NO3--N concentrations in groundwater from farmlands along the rivers increased from upstream to downstream. NO3--N concentrations in groundwater from corn fields decreased toward the rivers, related negatively with groundwater tables and positively with nitrogen fertilizer applications. There might be potential risks for NO3--N concentrations exceeding the WHO limit as groundwater tables are lower than 7 meters or annual fertilizer applications are more than 200kgN /hm2 in corn fields.