“稻转旱”对低山丘陵区氮素流失通量的影响——以三峡库区渠溪小流域为例

为探究“稻转旱”的土地利用变化对区域氮素流失的影响,以三峡库区渠溪小流域为研究对象,利用土地利用转移矩阵揭示了该流域2001—2019年的土地利用变化,基于输出系数模型并利用流域氮负荷实测数据进行模型参数修订后,对该流域2001年和2019年氮负荷进行了估算并比较。结果表明:该流域2001—2019年土地利用总体演变趋势为水稻田向旱地转化、旱地向林地转化,且以“稻转旱”为主。这种演变使流域氮素流失增加,2019年相对于2001年氮流失量增加了26%,平均每公顷氮流失量增加了约7.8 kg。这种变化表明在农业结构调整时应考虑到水稻田对面源污染物氮素良好的净化拦截作用,控制其面积的缩减以及在小流域氮素输移关键节点上的布局。

Conversion of Rice Paddy into Dry Land and Its Influence on Nitrogen Fluxes in the Low Hilly Area-A Case Study of the Quxi Basin in the Three Gorges Reservoir Area

To explore the effect of the land conversion of rice paddy into dry land on regional nitrogen loss,the land use change from 2001 to 2019 was identified by using the transfer matrix of land use in the Quxi Basin of the Three Gorges reservoir area.The nitrogen loads of the basin from 2001 to 2019 were calculated and compared by the export coefficient model with the parameters modified by the measured nitrogen load data of the basin.The results showed that from 2001 to 2019 the overall shifting trend of land use in the basin was the conversion of rice paddy into dry land and dry land into woodland,and the conversion of rice paddy into dry land was the main trend.This land conversion resulted in 26%increase in nitrogen loss in 2019 compared with that in 2001,with an average increase of about 7.8 kg/hm².The results indicate that,in facing the rapid agricultural land-use change,the significant role of paddy field in purifying and intercepting non-point source nitrogen should be taken into account,paddy field area of given size shall be maintained,and paddy field shall be designed at some key nodes of nitrogen transport in the small watershed agricultural landscape.These results can provide a new insight of a regional control of non-point source pollution in coping with the environmental changes.