当前河流筑坝导致水库释放温室气体N2O 的问题已经引起了世界范围内的广泛关注,梯级开发河流N2O 释放过程和机理的研究有助于准确评估河流N2O 释放水平. 本研究选取了乌江中上游梯级开发河段, 采集了河水、库区表层水和水库下泄水样进行了相关地球化学分析. 结果显示, 乌江干流的梯级开发对水化学条件、氮化物以及N2O 的释放产生了显著影响, 氮化物受到显著的拦截效应, N2O 在库区附近的释放明显强于河流. N2O 饱和度平均为347%, 均表现为大气N2O 的释放源, 并受各水库自身库龄、营养状态和有机质等条件的影响.春夏季受水库内部氮的生物地球化学影响,具有较高的N2O释放水平. 温度、酸碱度(pH)和溶解氧(dissolved oxygen, DO)是影响N2O 释放的关键因子, 对于库龄较老的乌江渡和东风湖来说, 有机碳埋藏和水库营养条件显著促进着N2O 的释放, 而氮负荷水平并未表现出显著促进N2O 的释放. 硝化作用是河流N2O 产生的主要过程, 但是下泄水较高的NN2O 含量说明库区底部反硝化作用具有重要的贡献. 全年河流水-气界面释放通量平均为0.33 μmol·m−2·h−1, 下泄水的释放通量为0.64 μmol·m−2·h−1, 水库表层水释放通量为0.43 μmol·m−2·h−1. 与世界其他河流相比, 乌江中上游干流N2O 的释放水平属中等水平, 主要控制因素可能是氮负荷水平和水体水化学条件. 然而, 下泄水体具有高于河流和库区表层水的释放通量, 需要引起重视.
Dams affect hydrologic cycle and water environment through intercepting river water. Therefore, “impounded rivers” or river reservoirs often affect river basin environments. That has become a worldwide problem, especially the effect on N2O emissions. This study investigates cascade reservoirs in the Wujiang River, and analyzes therelated parameters and N2O concentrations. It has been shown that the cascade development doeshave impacts on water parameters, nitrogen loadings and N2O emission. Saturation of N2O averaged 347% in the entiresurface water represents a N2O source with respect to atmosphere,
under influences of age of reservoirs, nutrient status and organic matters. N2O is emitted more in spring and summer than in winter and autumn. The key factors of influence are T, pH and DO. Organic matters and nutrient status are important in old reservoirs such as the Wujiangdu reservoir. Nitrification is a dominate process for N2O emission in surface water. But for water in discharge, denitrification is a dominate process. The annual average N2O fluxes were 0.33 μmol·m−2·h−1 for river water, 0.64 μmol·m−2·h−1 for discharge water, and 0.43 μmol·m−2·h−1 for surface water in dams. Compared to other surface water
in the world, emission of N2O acts as moderate emission fluxes in the Wujiang River. High concentration in discharge water should be emphasized since it contributes huge amount of N2O emission during hydroelectric production.
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