土地利用/覆盖对华南地区感潮河流碳分布格局的影响

河流是陆海碳输送的主要通道，在全球碳循环中发挥着重要作用. 随着城市化进程的加快，河流碳分布格局将会改变. 本研究于2019年11月(枯水期)和2020年7月(丰水期)对珠江三角洲地区潭江流域干支流开展有机碳、无机碳等水质指标监测，基于土地利用数据划定流域分区和沿河岸不同距离(500、1 000、1 500、2 000和2 500 m)缓冲区，采用差异性分析、Spearman相关性分析、冗余分析(RDA)等手段，分析土地利用格局对华南地区感潮河流碳浓度分布格局的影响. 结果表明:①水体TOC(总有机碳)、TIC(总无机碳)平均值分别为(3.50±0.92)(2.61±2.10) mg/L，区域TOC、TIC浓度存在时空分布差异，丰水期TOC、TIC浓度均显著高于枯水期，感潮区TOC浓度显著高于非感潮区，建设用地占比高、林地占比低的核心城市生态区河流的TOC浓度较高. ②1 500 m缓冲区是流域内景观格局对碳浓度变化作用最强的河岸带宽度，对碳的总解释率为20.03%；城市区域的排放对有机物浓度影响严重，耕地、林地的拦截吸附作用使得河流中的有机碳浓度相对较低，连片坑塘、养殖池等对河流中营养盐浓度的影响较大. ③水体中碳、氮、磷等的正相关关系表明，水体污染与生活污水排放、养殖生产活动和农业面源污染等有关. 因此，加强缓冲区坑塘、养殖池等的污染控制以及建成区与河流间绿化建设，是控制潭江等华南地区感潮河流中碳浓度以及入海碳通量的关键管理手段. 

Land Use Drives the Spatial Patterns of Carbon in a Tidal River in Southern China

Carbon transfer along the land-river-ocean continuum is an important component of the global carbon cycle. The combined pressures of coastal development and land use change are dramatically altering carbon dynamics in tidal rivers. To explore the carbon patterns in subtropical tidal rivers in Southern China, we collected 29 water samples from the mainstream and tributaries of the Tan River in November 2019 (dry season) and July 2020 (wet season), and measured the total organic carbon (TOC), total inorganic carbon (TIC) and general water quality indices. In addition, the characteristics of land use and landscape patterns in different regions and multiscale buffer zones (500, 1000, 1500, 2000 and 2500 m) were analyzed. Spearman correlation analysis, redundancy analysis (RDA) and other methods were used to quantify the impacts of land use change on the concentrations of carbon. The results showed that: (1) The overall mean concentrations of TOC and TIC were (3.50±0.92) mg/L and (2.61±2.10) mg/L, respectively, with significant spatial and temporal variability. Both TOC and TIC in the wet season were significantly higher than those in the dry season. The TOC was high in the tidal reach of the core urban ecological area, where the proportion of urban land was high, and the proportion of forest land was low. (2) The landscape pattern index of the buffer zone at different spatial scales had a good explanatory degree for water quality, and the landscape structure of the buffer zone at 1500 meters had the strongest explanatory ability for carbon concentration (20.03%). Sewage-dominated urban river network had more organic matter, while the rural branch had less organic matter due to plant interception and absorption. The surrounding ponds were responsible for the high nutrient concentrations in rivers. (3) Meanwhile, the significant positive correlation among carbon and other nutrients indicated that water pollution was related to domestic sewage discharge, aquaculture production activities and agricultural non-point source pollution. This research reveals that the carbon concentration in tidal rivers and flux to estuaries can be reduced by strengthening management policies of land use patterns in buffer zones, especially those regarding pollution control of the surrounding ponds, and creating green belts between urban construction and rivers.