紫色土坡耕地可溶性有机碳径流迁移特征

Characteristics of dissolved organic carbon transport via overland flow and interflow on sloping cropland of purple soil

为探明紫色土坡耕地可溶性有机碳(dissolved organic carbon,DOC)的径流迁移特征,该文通过具有壤中流观测功能的径流小区观测地表径流和壤中流的可溶性有机碳(DOC)迁移。结果表明,径流方式对紫色土坡耕地径流DOC迁移质量浓度具有明显影响。地表径流过程中DOC质量浓度随降雨历时逐渐降低,而壤中流过程DOC质量浓度则表现出先升后降而后趋于稳定的趋势。暴雨和大雨地表径流和壤中流过程中DOC质量浓度均表现出不同的变化特征。暴雨地表径流过程DOC初始质量浓度高,衰减快,壤中流DOC质量浓度高、峰值出现较早。2010、2011年2a内地表径流和壤中流平均累积径流量分别为61.2、300.3mm,平均径流系数为7.7%和37.6%。2a内次降雨产流事件中地表径流和壤中流DOC平均质量浓度分别为3.9和3.4mg/L,壤中流DOC年平均迁移通量为105.2mg/m2,年平均负荷达1007.6mg/m2,约为地表径流的4.8倍,壤中流携带DOC损失是紫色土坡耕地DOC径流迁移的主要方式。土层温度是影响壤中流DOC质量浓度季节性变化的重要因素,二者具有显著的负相关性(P<0.05),而土层温度对地表径流DOC质量浓度季节性变化无显著影响。该研究可为调控紫色土坡耕地DOC流失提供一定的参考。

Runoff is a major driver for Dissolved Organic Carbon （DOC） diffusing into aquatic ecosystems. The transportation of DOC during storm events could have measurable impacts on the global carbon cycle, but the magnitude and pathway of the impacts remain uncertain due to a lack of data. A better understanding of DOC transport via overland flow or interflow on sloping cropland is favorable for the carbon sequestration of cultivated upland. This study aimed to gain insight into the process and flux of transport of DOC in runoff as affected by rainfall characteristics. An experiment was conducted to monitor DOC transport via overland flow and interflow on sloping cropland of purple soil with free-drain lysimeter at Yanting Agro-ecological Experimental Station, Chinese Academy of Science. The experimental plots were conducted in traditional mineral fertilizer treatment （NPK） with fertilization rates at 130 kg/hm2 of N, 90 kg/hm2 of P2O5, 36 kg/hm2 of K2O for wheat and 150 kg/hm2 of N, 90 kg/hm2 of P2O5, 36 kg/hm2 of K2O for maize growing seasons, respectively. DOC transport via overland flow and interflow was continuously monitored from 2010 to 2011 in the rainy seasons by determining DOC concentrations via means of flow injection analysis （FIA） technology by Auto Analyzer3 （AA3, Bran＋Lubbe, Norderstedt, Germany）. Results indicated that DOC concentration was greatly affected by overland flow and interflow process. DOC concentrations in the drainage water of overland flow exhibited sharp declines at the initial period, whereas those in interflow increased at the initial period of a rainfall event and declined steadily. Transport processes of DOC were greatly affected by rain intensity. DOC concentration in the initial stage of overland flow was high while the peak DOC concentration in interflow was higher and occurred earlier in storm rain compared with heavy rain event. Average annual cumulative discharge of overland and interflow from 2010 to 2011 was 61.2、300.3 mm, accounting for 7.7% and 37.6% in the whole rainy season respectively. The average DOC concentrations in overland flow and interflow were 3.9 and 3.4 mg/L, respectively, during the experiment period. Average DOC transport fluxes and annual cumulative loads of interflow were 105.2 and 1007.6 mg/m2, respectively. The average transport load of DOC in interflow was 4.8 times more than that in overland flow. It indicated that interflow was the main transport pathway of dissolved organic carbon in the rainy season. Furthermore, soil temperature measured at soil depths （5, 20, 40, and 60 cm） had a significant negative correlation on DOC concentration in interflow while there was no effect on DOC concentration in overland flow, causing greatly different seasonal and annual patterns of dissolved organic carbon concentration in interflow.