巢湖流域地下水硝态氮含量空间分布和季节变化格局

2009年冬季、2010年春季和夏季分别在巢湖流域采集了253个、249个和230个水井的地下水样品,分析了其硝态氮含量。结果表明,巢湖流域的地下水硝酸盐污染比较严重,冬季、春季和夏季的地下水硝态氮的超标率(≥10 mg/L)均超过20%。巢湖北部区的地下水硝态氮含量高于南部地区。在巢湖北部区,东北部江淮分水岭丘陵区的地下水硝态氮含量较低。在巢湖南部区,地下水硝态氮含量具有从西部山区向东部平原逐渐升高的趋势。不同土地利用类型的地下水硝态氮含量排序是村庄菜地旱地乡镇水稻-油菜(或小麦)轮作田果园单季水稻田养殖场,传统水稻田绿色水稻田。巢湖流域地下水硝态氮含量的季节变化总趋势为冬季≈春季夏季,主要与降水有关。不同土地利用类型的地下水硝态氮含量的季节变化格局不同,其中地下水硝态氮含量呈现冬季春季夏季的土地类型为菜地、果园和水稻田,春季冬季夏季的土地类型为旱地、乡镇、畜禽养殖场,春季夏季冬季的土地类型为村庄,这种季节变化格局主要与不同土地利用类型的施肥量、施肥时间的不同有关。

Spatial and seasonal variations of nitrate-N concentration in groundwater within Chao Lake watershed

253, 249 and 230 water samples from wells in Chao Lake watershed were respectively obtained in winter(2009), spring(2010) and summer(2010), and analysed for nitrate-N to discover its spatial and seasonal patterns. Groundwater nitrate contamination in Chao Lake watershed is severe, which more than 20% of shallow wells sampled in winter, spring and summer, respectively, show groundwater nitrate-N exceed 10 mg/L, the WHO limit for drinking water. The groundwater nitrate-N concentration in the north region of Chao Lake watershed is higher than that in the south region. The nitrate-N concentration in the south region decreases from western hill to eastern plain while that in the north region is lower in north-east part which is the divide between Yangtze River and Huai River. Rank of nitrate-N concentration in different land uses is village > vegetable land > dryland > town > rice-rape (or wheat) cropping field > orchard > single cropping rice field > livestock farm. In general, the nitrate-N concentration highlights significantly seasonal pattern with that being almost the same in winter and spring, and higher than that in summer from the whole Chao Lake watershed. However, seasonal patterns of nitrate-N concentration are different in different land use types, which the pattern of winter > spring > summer is found in vegetable land, orchard and rice field, that of spring > winter > summer in dry land, town and livestock farm, and that of spring > summer > winter in village, possibly due to different time and amount of fertilizer application.