土地利用和覆被方式的转变对太原城市滨水生态系统碳水通量的影响

As an indispensable part of the urban development, the urban waterfront has a uniquely complicated environment, and it also presents a sensitive reaction to human activities. Meanwhile, the waterfront zone is the most fragile and most responsive to change in urban areas. The land use/ cover change (LUCC) caused by urbanization cast an obvious influence to riverside vegetation and soil environment. Compared to other urban zone, the change of original natural earth surface would bring a different variation in surface energy balance, land-atmosphere material exchange, and turbulent features. Thus the urban climate and environment is largely impacted by the variation. As the coming forth of eddy covariance (EC) technique, the capacity of ecosystem carbon-water exchange and the components of energy balance would be individually and quantitatively measured, which has achieved success in natural ecosystem like forest, wetland, grassland and cropland. This research intends to adopt a moveable flux system to carry out a long-term consecutive measurement of CO2 and H2O in Taiyuan's urban waterfront ecosystem under different land use/cover types. The research focuses on the quantitative relation and correlative feature among single and composite vegetations of constructed wetland, lawn, planted forest and original bare land. Combining the periodical vegetation inventory and sampling analysis, the carbon sequestration and water balance through the diverse land use/cover change will be identified, thus, to provide scientific evidence for predicting possible influence and changing trend of urban waterfront ecosystem in contribution to regional carbon, water and energy balance.

作为城市拓展的重要部分，城市滨水区具有特殊复杂的环境并且受到人类活动的强烈干扰，是城市发展中最为脆弱、最易受变化影响的区域。城市化所引起的土地利用和覆被变化使得沿河植被和土壤环境发生明显改变，进而导致地表能量平衡、地-气间物质交换、湍流特征将与城市其他区域有很大不同，这必然会深刻地影响城市气候和城市环境。随着涡度相关技术的出现，生态系统碳水交换和能量平衡各分量都可以被独立量化，且已成功应用于森林、湿地、草地和农田等自然生态系统。本研究拟采用调节式可移动通量观测系统，对城市滨水区不同土地利用和覆被方式下的碳水通量进行长期连续观测，重点考察城市人工湿地、草坪、片林、复合绿地与原始裸地的碳水通量间的定量关系与差异特征。结合周期性植被调查和取样分析，确定土地利用和覆被方式的转变对城市生态系统碳水平衡的影响及作用因子，为预测城市滨水生态系统对区域碳、水和能量平衡的可能影响和变化趋势提供科学依据。

城市化所引起的土地利用和覆被变化使得城市滨水区植被和土壤环境发生明显改变，进而影响了地表能量平衡、地气间物质交换及湍流特征，目前缺少关于城市滨水生态系统碳水通量的定量研究。本项目的总体研究目标是揭示太原汾河不同植被下垫面的碳汇强度及其作用因子，虽然只有一个生长年的观测周期，但重点考察了人工湿地的生态效益，为城市滨水资源的合理利用与适应性管理提供科学依据。太原汾河人工湿地在观测期内总体表现为碳源，释放了67.63gC m-2。虽然冬季水生植物基本已枯萎，呼吸作用较弱，但进入冬季后，仍然有数日为净碳吸收，温度变化导致的CO2的溶解度变化对其通量的影响是不容忽视的，夜间温度的降低，CO2在水中的溶解度增加，所以夜间有些时间仍为CO2的汇。水气界面处CO2的分压差（浓度差）是影响CO2通量的重要因素，与pH、溶解氧、温度、风速都有着直接关系。系统蒸散日均值为1.05mm/d，累计值120.07mm，而总降水量只有33.4mm，蒸散远大于降水，汾河人工湿地的蒸散发和饱和水气压亏缺显著相关。