太湖丘陵地区农田氮素迁移的时空分布特征

在太湖丘陵地区选择4种有代表性的土地利用类型进行野外原位试验,研究自然降雨条件下氮素随地表径流迁移的时空分布特征.试验结果表明,随地表径流迁移的农田氮素以氨氮为主,其“次降雨径流平均浓度”中位值占总氮的44.5%,亚硝态氮浓度最小,仅占1.8%.地表径流中的氮素浓度存在显著的季节性差异,其分布主要受降水量、气温等气象条件以及农事活动的影响.总氮、氨氮、硝态氮和亚硝态氮的“多场降雨径流平均浓度”的时间变异性依次减小.菜地径流中总氮、氨氮和硝态氮以及竹林亚硝态氮的SMC值最高,不同土地利用下氮素浓度的空间分布主要与施肥条件以及植被覆盖度有关.各氮素形态SMC值的空间变异性小于其时间变异性.旱地和菜地的氮素迁移通量大于板栗林和竹林,径流量是导致迁移通量存在显著差异的主导因素.

Temporal and Spatial Distribution Characteristics of Nitrogen Losses in Hilly Area of Taihu Lake

Four typical land uses in hilly area of Taihu Lake were studied on temporal and spatial distribution characteristics of nitrogen losses in surface runoff under natural rainfall through experiment in situ.The medium value of event mean concentration(EMC) of ammonia nitrogen(NH₄⁺-N) which dominated agricultural N in surface runoff accounted for 44.5% of total nitrogen(TN),while nitrite nitrogen(NO₂^--N) accounted for 1.8%.Concentration of nitrogen in runoff had significantly seasonal variation which was related to meteorologic conditions such as rainfall,temperature,and agricultural activities.Temporal variabilities of site mean concentration(SMC) for TN,NH₄⁺-N,NO₃^--N and NO₂^--N were decreased sequentially.The highest SMC value of TN,NH₄⁺-N and NO₃^--N in upland runoff and NO₂^--N in bamboo grove were observed.The spatial distribution of nitrogen losses was determined by fertilizer application and vegetation coverage.Spatial variabilities for SMC of nitrogen were less than temporal variabilities.It was found that transportation fluxes of nitrogen in surface runoff from upland and vegetable plot were higher than that from chestnut orchard and bamboo forest which have significantly related to surface runoff volume.