同位素溯源解析地下水库对地下水氮分布影响

2016-10-19康萍萍许士国禹守泉

水资源保护 2016年5期

关键词：莱州市库区同位素

康萍萍,许士国,禹守泉

(1.大连理工大学水利学院水环境研究所,辽宁大连　116024; 2.莱州市水务局,山东莱州　261400)

同位素溯源解析地下水库对地下水氮分布影响

康萍萍1,许士国1,禹守泉2

(1.大连理工大学水利学院水环境研究所,辽宁大连116024; 2.莱州市水务局,山东莱州261400)

地下水库;氮氧同位素;环境影响;氮来源;IsoSource;氮贡献比例

1　材料与方法

1.1研究区概况

王河流域位于山东省莱州市东北部。气候属于暖温带东亚季风区大陆性气候。多年平均气温为12.4℃,多年平均降水量为1 172.4 mm,多年平均蒸发量为2 039.6 mm。5月和6月蒸发量最大,是同期降雨量的9～16倍。地下水补给以大气降水、王河地表水下渗和海水倒灌为主。流域内土地利用以耕地为主,分布着村庄,东部近海区分布着大面积的海水养殖池。

自1977年以来,王河流域多年持续干旱,水源紧缺,为了满足工农业及生活用水需要,流域内开始开采地下水。到1980年,年平均超采地下水0.61亿m3,使地下水位大幅度下降。1977—1992年间全市地下水位总计下降8.02 m,负值区达282.2 km2。超采改变了地下淡水与海水之间的极限平衡,造成海水大面积入侵。截至1992年底,海水入侵面积达到234.15 km2，近1.33万hm2农田荒废,平均减产40%。为了充分利用王河流域水资源,抑制莱州湾海水进一步入侵，在王河下游修建了王河地下水库。

王河地下水库位于莱州市西北15 km处、西由村附近王河下游,距离莱州湾约2 km。王河地下水库东倚山前岗地,西与渤海平原相接,东西宽5～9 km,南北为呈带状展布的冲洪积平原。地下水库含水层岩性为砾质粗砂、微含土砾质粗砾、中细砂及沙壤土。王河地下水库总库容为5 693万m3,最大调节库容为3 273万m3,最高运行水位为1.0 m, 死水位为-9.0 m, 工业用水日供水量为3万t。地下坝主要包括北坝、西坝、副坝地下防渗墙工程。北坝西起仓上村北,东至街西村西北,坝长2.7 km,西坝南起朱由镇武家村龙王河北岸,北与仓上残丘相接,坝长8.25 km,副坝位于西由镇新合村南,坝长0.84 km。地下坝防渗墙采用高压摆喷灌浆、高压定喷灌浆和高压旋喷灌浆。库区内土地利用类型主要是耕地和村庄,库区外土地利用类型较为复杂,西部近海区主要是海水养殖,内陆区主要是耕地和荒地,零星分布着村庄。

1.2地下水样品采集

图1　研究区位置及采样点分布

1.3氮浓度分析

1.4氮氧同位素分析

(1)

式中:Rsa和Rst分别为样品和标准样品的15N/14N和18O/16O比值。

(2)

(3)

表1　王河地下水库内外地下水水样检测结果

2　结果分析与讨论

2.1库区内外地下水中氮浓度特征

图2　不同来源[12]的和及王河地下水库的和

图3　王河地下水库库区内外地下水中与的关系

图4　王河地下水库库内地下水污染源贡献比例

图5　王河地下水库库外地下水污染源贡献比例

3　结　语

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Analysis of influence of underground reservoir on nitrogen distribution through tracing of isotope source

KANG Pingping1, XU Shiguo1, YU Shouquan2

(1.InstituteofWaterandEnvironmentalResearch,FacultyofInfrastructureEngineering,DalianUniversityofTechnology,Dalian116024,China;2.LaizhouWaterAuthority,Laizhou261400,China)

Taking the Wanghe River Underground Reservoir in Shandong Province as an example, we used nitrogen and oxygen isotopes to analyze the distribution, sources, and transformation of nitrogen in groundwater. We used the IsoSource software to calculate the contribution ratios of different pollution sources, in order to analyze the influence of the underground reservoir on nitrogen distribution in groundwater. The results show that NO3-and TN in groundwater within the underground reservoir had higher concentrations and smaller spatial differences than they did outside of the underground reservoir, and the main nitrogen source was fertilizer in groundwater within the underground reservoir. Denitrification occurred in groundwater within the underground reservoir. The nitrogen in groundwater outside of the underground reservoir was mainly from mariculture and fertilizers. All the results mentioned above indicate that the underground reservoir prevents nitrogen from flowing horizontally, resulting in the accumulation of nitrogen and the enhancement of denitrification of nitrogen in groundwater within the underground reservoir.

underground reservoir; nitrogen and oxygen isotopes; environmental effects; nitrogen sources; IsoSource; nitrogen contribution ratio