作 者 ：徐华山,赵同谦*,贺玉晓,徐宗学,马朝红
期 刊 ：生态学报 2010年 30卷 21期 页码：5759~5768
Keywords:riparian wetland, vegetation plot, agriculture, non-point source, nitrogen,
摘 要 ：教育部新世纪优秀人才支持计划项目(NCET-09-0120); 中国科学院城市与区域生态国家重点实验室开放基金(SKLURE2010-2-4); 国家自然科学基金项目(30570276); 河南省教育厅自然科学研究计划项目资助(2010B610006)
Abstract:As a functional transition interface connecting rivers and lands, riparian wetlands are one of the major transition zones for matter, energy, and information transfer between aquatic and terrestrial ecosystems. It is also the last barrier to protect the water quality in rivers, and play an important role in water purification and non-point pollution control. With the combination of field experiments and isotope trace technique (the 15N-enriched method) in Kouma section of the Yellow River, retention of agricultural non-point nitrogen pollution by the soil in riparian wetland, the proportion of agricultural non-point nitrogen which leaks into the groundwater, and the absorption of agricultural non-point sources nitrogen pollution by different vegetation types in riparian wetlands were investigated. The results showed that the agricultural non-point sources nitrogen flowing into riparian wetlands through surface runoff infiltrated into the subsurface and dispersed both vertically and horizontally in three experiment plots. Retention of agricultural non-point nitrogen pollution by the soil in riparian wetlands mainly occurred in the soil layer at top 0-10 cm, and the amount of nitrogen retained by surface soil associated with three types of vegetation were 0.045 mg/g for Phragmites communis Trin plots, 0.036 mg/g for Scirpus triqueter plots, and 0.032mg/g for Typha angustifolia plots, which accounted for 59.2%, 56.3%, and 56.1% of the total nitrogen interception, respectively. The top soil layer (0-10 cm) of riparian wetland acts as a filter. A long period pollution effect exists in agricultural non-point nitrogen that remained in the soil. Strong denitrification function of soil microorganisms in the extraordinary oxidation-reduction condition of riparian wetland and uptake by plant in riparian wetland make agricultural non-point nitrogen in the 0-10 cm soil layer change more quickly than those in other layers. After K15NO3 was added to the surface soil, nitrogen content decreased by 77.8% for Phragmites communis Trin plots, 68.8% for Typa angustifolia plots, and 8.3% for Scirpus triqueter plots within one month, respectively. Three months later, the nitrogen content decreased by 93.3% for Phragmites communis Trin plots, 72.2% for Scirpus triqueter plots, and 37.5% for Typa angustifolia plots, respectively. Due to complex hydrological processes in riparian wetlands, it is more complicated for agricultural non-point sources nitrogen remaining in the surface soil to transfer and transform. Monitoring data indicated that groundwater was not affected by agricultural non-point pollution at this experimental concentration through detention by the soil in riparian wetland. But one month later, 15N atom percentage showed significant difference comparing with other time, and it is probably because of frequent exchange between groundwater and river water in the study area. Effects of agricultural non-point nitrogen pollution were significantly different among different vegetation communities. Effects of agricultural non-point nitrogen pollution were also significantly different among different growth stages of the same plant. The nitrogen uptake amount changed as follows: young shoots of Phragmites communis Trin plots (9.731 mg/g) > old Phragmites communis Trin plots (4.939 mg/g) > Scirpus triqueter plots (0.620 mg/g) > Typa angustifolia plots (0186 mg/g). Harvesting of Phragmites communis Trin vegetation at midseason can promote its absorption for agricultural non-point nitrogen pollution. The nitrogen uptake amount of Phragmites communis Trin plots, Typa angustifolia plots, Scirpus triqueter plots were 96.11kg/hm2, 3.76 kg/hm2, and 0.32 kg/hm2, respectively. This study suggests that riparian wetlands play a key role for the control of agricultural non-point pollution. As the buffer connection between rivers and lands, the riparian wetland can effectively reduce the agricultural non-point nitrogen pollution through interception, filtration, plant uptake and other processes. The scientific protection and utilization of riparian wetland will be helpful to protect water environment in rivers.
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