九龙江流域河流氮输出对土地利用模式和水文状况的响应

流域土地利用模式与水文状况影响河流氮的来源、迁移转化和输出，关乎流域健康与淡水生态系统服务的供给.本研究基于2010~2017年观测数据，采用流域模型、地理信息技术和数理统计等方法从多时空尺度探究亚热带中尺度近海流域——九龙江流域河流氮输出对流域土地利用模式和水文状况的响应机制.结果表明，NO₃^--N是九龙江流域河流水体主要的无机氮形态；农业和城市流域河流水体的氮浓度、输出负荷及其年际与季节变异性高于自然流域；丰水年各类流域河流水体的氮浓度和输出负荷差异总体上高于枯水年；相比水文状况，土地利用与氮年均浓度和输出负荷的正相关性更显著.总体而言，河流氮输出时空变化特征受流域土地利用模式和水文状况的共同作用.

Response of Riverine Nitrogen Exports to Land Use Pattern and Hydrological Regime in the Jiulong River Watershed

Watershed land use patterns combined with hydrological regimes affect riverine nitrogen (N) sources, transformation pathways, and exports, which can affect watershed health and freshwater ecosystem service supply. Understanding how land use and hydrological regimes affect riverine N exports is therefore useful for developing sustainable watershed management strategies. Based on in-situ observations during the period 2010-2017, watershed modeling, geospatial technology, and statistical analysis were coupled in this study to explore the responses of riverine nitrogen exports to watershed land use pattern and hydrological regime in a medium-sized watershed. Results showed that nitrate was the major form of dissolved inorganic N in the Jiulong River watershed; agricultural and urban watersheds had higher N exports and greater temporal variability than those in natural watershed. The seasonal fluctuation for watershed N concentrations and exports was obvious in wet years compared with dry years. Compared with the hydrological regime, the land use pattern had significant effects on N concentrations and exports. This study demonstrated that spatiotemporal variations of riverine nitrogen exports were mainly contributed by the coupled effects of watershed land use pattern and hydrological regime.