红壤区农地坡面构型对土壤水文过程及氮流失影响

Soil erosion and non-point source pollution are important ecological issues of agricultural land in red soil region. Being the most widely used soil and water conservation engineering measure, terrace has significant effects on soil and water conservation. While the effect on soil hydrological processes and nitrogen loss of its slope configuration, which is utterly different from that of natural slope, still remains unclear. Therefore, terrace and straight slope were selected as the two typical slope configuration in the study. It conducted high frequency monitoring for soil moisture constantly and long-term stationary experiment for runoff plots under natural rainfall. Specifically, it monitored different parts of terrace and straight slope for their soil moisture change of different depths, runoff process of surface and subsurface, as well as their accompanying nitrogen loss. After analyzing the temporal and spatial dynamic distribution pattern of soil moisture, runoff process and nitrogen loss characteristics, hot spots and active periods of soil water movement were identified and the nitrogen loss flux and the major loss path were confirmed. At the same time, the effect on moisture movement, runoff and nitrogen loss in process of slope configuration was clarified, and influence mechanism of the slope configuration on soil hydrological processes and nitrogen loss was revealed by applying the comparative study and multivariate statistics. This study is expected to provide the scientific basis and theoretical support for soil erosion and non-point source pollution control and finally promote the comprehensive improvement of agricultural land in red soil region.

水土流失和面源污染是红壤区山坡农地面临的重要生态问题。梯田作为区域内应用最为广泛的水土保持工程措施，水土保持效果显著，但其迥异于自然坡面的特殊坡面构型（由外高内低田面和陡坡田坎组成、地形连续突变）对土壤水文过程及氮流失的影响机制还不明晰。因此，本研究选取梯田和直坡这两种典型坡面构型的农地为研究对象，开展土壤水分高频连续监测与自然降雨条件下径流小区长期定位试验。监测梯田和直坡不同部位分层土壤含水量变化、地表径流和壤中流产流过程及其伴生的不同形态氮素含量，分析土壤水分时空分布格局、坡面产流过程及氮流失特征，识别土壤水分运移活跃区域和时段，明确不同形态氮流失通量及主要途径，并通过对比研究及多元统计方法，阐明坡面构型对水分运移、坡面产流及氮流失过程的影响，揭示坡面构型对土壤水文过程及氮流失的影响机理。本研究可以为红壤区山坡农地综合整治过程中针对性地开展水土流失与面源污染防治提供科学依据和理论支持。

水土流失和面源污染是红壤坡地面临的重要生态问题。梯田作为区域内应用最为广泛的水土保持工程措施，水土保持效果显著，但其迥异于自然坡面的特殊坡面构型对土壤水文过程及氮流失的影响机制还不明晰。本项目选取直坡和梯田坡面，开展自然降雨条件下的径流小区试验和人工模拟降雨条件下的实验土槽试验，通过高频连续监测土壤水分和逐降雨场次监测坡面产流产沙及氮流失状况，系统分析土壤水分时空分布格局、坡面产流过程及氮流失特征，发现：（1）降雨初期是土壤含水量变动最剧烈时段，降雨过程是土壤水分运移最活跃时期；（2）受梯面出露、土壤水分损耗增加影响，前期长期无降雨时，梯田坡面土壤含水量相对更低；（3）梯田通过储存土壤水分，能够显著减少强降雨时期坡面产流，对地表径流具有拦截效果，但在一定程度上会增加壤中流，且遭遇超强降雨时（降雨量>110mm），梯田可能导致产流增加；（4）自然降雨条件下，壤中流为径流的主要成分，强降雨事件红壤坡地产流更多，且壤中流表现更为明显；超强降雨事件中，坡面产流以地表径流为主；（5）溶解态氮（尤其是硝态氮）是径流氮素流失的主要形态，壤中流是自然降雨条件下坡面氮素流失的关键途径，强降雨事件是坡面氮素流失的重点时段，地表径流是强降雨过程中氮素流失的关键途径，梯田能在一定程度上降低红壤坡面径流氮素浓度，减少氮素流失；（6）土层深度、土粒密度、饱和含水量、毛管断裂含水量是坡面土壤水分空间分布关键影响因素，降雨量、降雨历时、瞬时雨强和表层土壤初始含水量是坡面产流关键影响因素，降雨量、降雨历时、瞬时雨强、径流量、径流系数、总径流壤中流占比、地表径流含沙量、泥沙流失量是试验坡面氮素流失的关键影响因素。在本项目资助下，共发表论文5篇，其中SCI收录3篇、EI收录1篇。本项目研究成果可以为红壤坡地综合整治过程中针对性地开展水土流失与面源污染防治提供科学依据和理论支持。