洪泽湖地区麦稻两熟农田及杨树林地降雨径流对地下水水质的影响

Effects of rainfall and runoff on the groundwater quality in farmland and poplar forestland in the area of Hung-tse Lake

农业氮磷养分流失已经成为地下水污染的重要原因之一,为了探究和比较麦稻两熟农田和杨树林地氮磷流失对地下水的影响,本文在洪泽湖河湖交汇区设置农田和杨树林监测小区和监测井,进行了为期1 年的地表养分流失和地下水水质监测。结果表明: 1)林地雨前雨后表层土壤含水量均小于麦田,麦田土壤含水量较雨前平均提高8.95%,林地提高4.05%。2)麦田和杨树林地表层土壤硝态氮、铵态氮及有效磷流失总量分别为63.53 mg·kg^-1、5.61 mg·kg^-1 及57.43 mg·kg^-1 和16.78 mg·kg^-1、2.45 mg·kg^-1 及0.73 mg·kg^-1,稻季田面水硝态氮、铵态氮、可溶性磷和颗粒态磷流失总量为8.32 mg·L^-1、27.44 mg·L^-1、2.39 mg·L^-1 和2.99 mg·L^-1,监测期内杨树林氮磷流失总量明显低于农田。3)农田表层养分流失量与降雨量存在密切关系,基本随降雨量增大呈对数增长,而杨树林几乎不受降雨影响。4)农田产生径流的理论最小降雨量(麦田: 3.3 mm;稻田: 4.2 mm)远小于杨树林地(22.8 mm),麦田铵态氮、正磷酸盐浓度,稻田和杨树林地总氮、硝态氮、铵态氮、总磷、可溶性磷、正磷酸盐浓度与降雨量存在显著相关性。5)农田径流中养分浓度与地下水氮磷含量存在显著相关性(P<0.05),而杨树林地地下水氮磷含量保持在相对稳定水平,与径流中养分浓度无明显相关性。与农田相比,林地能够更好地控制径流养分流失,缓解地下水污染,有利于农业面源污染的控制。

The loss of nitrogen and phosphorus in agriculture has become an important cause of groundwater pollution. To explore and compare the losses of nitrogen and phosphorus from runoff in wheat fields, rice fields, and poplar forestland, the surface nutrient losses and groundwater quality were monitored in the area of Hung-tse Lake for one year, by setting up monitoring plots and monitoring wells on farmland and poplar forestland. The main results were as follows: 1) the surface soil water content before and after precipitation in the forestland was lower than that in the wheat field. The average soil water content in wheat fields was 8.95% higher than that before rain, whereas it was 4.05% higher than that before rain in forestland. 2) The total loss of nitrate nitrogen, ammonium nitrogen, and available phosphorus in the surface soil of the wheat field were 63.53 mg·kg^-1, 5.61 mg·kg^-1, and 57.43 mg·kg^-1;while those in the poplar forestland were 16.78 mg·kg^-1, 2.45 mg·kg^-1, and 0.73 mg·kg^-1, respectively. The total loss of nitrate nitrogen, ammonium nitrogen, soluble phosphorus, and particulate phosphorus in the surface water of the rice field was 8.32 mg·L^-1, 27.44 mg·L^-1, 2.39 mg·L^-1, and 2.99 mg·L^-1, and the total loss of nitrogen and phosphorus in the poplar forestland was significantly lower than that in the farmland during the monitoring period. 3) There was a close relationship between the soil nutrient loss and rainfall in farmland. The soil nutrient loss in farmland increased logarithmically with an increase in rainfall. However, the loss of surface nutrients in the poplar forestland was almost unaffected by rainfall. 4) The theoretical minimum rainfall generating runoff in farmlands (wheat field: 3.3 mm;rice field: 4.2 mm) was much lower than that of the poplar forestland (22.8 mm). The concentration of ammonium nitrogen, orthophosphate, total nitrogen, nitrate nitrogen, total phosphorus, and soluble phosphorus were significantly correlated with rainfall in wheat field. 5) There was a significant correlation between the nutrient concentrations in farmland runoff and nitrogen and phosphorus contents in groundwater (P < 0.05). The nitrogen and phosphorus contents in the groundwater of poplar forestland, which had no significant correlations with the nutrient concentrations in the runoff, remained at a relatively stable level. Compared with farmlands, forestland can better control nutrient losses caused by runoff, alleviate groundwater pollution, and contribute to the control of agricultural non-point source pollution.