横坡耕作径流溶解态氮磷流失特征及其富营养化风险--以鲁中南山地丘陵区为例

Characteristics of Dissolved N,P Loss and Eutrophication Risk in Runoff Water in Contour Tillage:A Case Study of Hilly and Mountainous Area in South-Central of Shandong Province,China

以鲁中南山地丘陵区的坡耕地为例,在模拟降雨条件下分析了横坡耕作地表径流溶解态硝态氮(DNN)、铵态氮(DHN)和磷(DIP)的流失特征,并通过溶解态无机氮DIN(DNN+DHN)/DIP、DNN/DIP和DHN/DIP等3种氮磷比衡量其径流的富营养化风险。结果表明,在研究区典型的暴雨强度下(70mm·h-1),横坡耕作产流所需降雨量在8.07mm左右,产流后径流率在径流初期(0～5min)迅速增加,并在末期(14min后)趋于稳定,而径流泥沙浓度在降雨过程的变化表现出单峰型特征;溶解态氮、磷浓度在径流过程中逐渐降低,其中,径流末期DNN、DHN和DIN的平均浓度较初期分别下降12.1%、23.5%和12.6%,DIP浓度的下降幅度明显大于溶解态氮,为32.5%;溶解态氮、磷浓度与径流率以及原表土速效养分含量在径流初期的相关程度较高,之后则逐渐降低,与泥沙浓度的相关系数在降雨过程中则呈高-低-高变化;各溶解态氮的流失率在径流过程中呈增加趋势,而DIP流失率在径流过程中的变化不显著;溶解态氮、磷流失率与径流率存在升幂函数关系,但相关性随径流时间延长逐渐减弱。N/P率分析表明,横坡耕作径流的富营养化风险较低,但风险水平在径流过程中呈逐渐增加趋势。控制径流末期DNN的径流流失,可减轻横坡耕作径流对于受纳水体富营养化过程的影响。

Simulative rainfall experiment was conducted in the sloping land with contour plowing in hilly and mountainous area in south-central of Shandong Province to analyze the loss characteristics of dissolved nitrate nitrogen（DNN）,ammoniacal nitrogen（DHN） and phosphorus（DIP） in runoff water,and measure the possible eutrophication risks in this water by calculating N：P ratios：（DNN＋DHN）/DIP,DNN/DIP,and DHN/DIP.Results showed that,under the typical torrentialrain intensity（70 mm·h-1）,the amount of precipitation necessary to produce runoff in contour tillage was 8.07 mm.After the runoff started,runoff rate obtained rapid increased in the initial runoff-stage（0~5 min）,and became stable after 14 min.The change of sediments concentration in the rain process presented a single-apex model.Dissolved nitrogen and phosphorus concentrations decreased gradually in the runoff process.The concentrations of DNN,DHN and DIN were 12.1%,23.5% and 12.6% less,respectively,in the final runoff-stage than that in the initial.The concentration of DIP decreased 32.5% which was significantly greater than that of the dissolved nitrogens.Dissolved nitrogen and phosphorus concentrations showed a high correlation with runoff rate and topsoil available nutrients at the initial runoff-stage,and then decreased gradually.The correlations between dissolved pollutant and sediments showed a high-low-high change in the rain process.The loss rate dissolved nitrogens increased significantly within the runoff process,while the difference of DIP loss in this process was not significant.The loss rate of dissolved nitrogen and phosphorus and the runoff rate performed a power function relationship,but this correlation was gradually reduced with runoff time extension.The analysis of N/P ratios suggested that runoff produced by contour tillage contour with a low eutrophication risk.However,the eutrophication risk level presented an increasing trend in the runoff process.Controlling the DNN loss at the final runoff-stage could effectively reduce the eutrophication risk of countor tillage runoff.