中文摘要：

流域的地貌和气候特征及干流筑坝等是影响河流碳动力学的主要因素。本文对干流下游筑坝的华南山地丘陵区河流增江的碳循环过程做了系统研究。结果表明，山地丘陵为主的流域地貌特征提高了增江河流碳的输出通量；而亚热带湿润气候和较高的森林覆盖率以及缺乏碳酸盐岩的流域地质背景使得溶解有机碳（DOC）构成增江河流碳的主要成分；光化学分解可以解释在秋季较强紫外线辐射下河水较低的DOC含量。受大坝影响河段水流速度的变缓为水生生物量的增加提供了条件，使得颗粒有机碳（POC）中来源于水生生物量的贡献率上升、有机物的C／N比降低。流速变缓的河道中藻类的生长导致水体CO2分压低于大气中的CO2分压。增江流域DOC和POC的输出通量分别为25．08×10^5g／kiM^2·a和11．58×10^5g／km^2a。本文为研究自然因素和人类活动对河流碳循环过程及通量的影响提供了一个典型案例。

英文摘要：

Geomorphic features, climate characteristics and dam construction are the main factors controlling the cycling and export of riverine carbon to the ocean. The Zengjiang River （ZJR） is a second-order tributary of the Pearl River system, with an area of 3160km2. Silicate rocks dominated the bedrock within the drainage basin. The landforms within the drainage basin are dominated by mountains and hills covered with a thick layer of red weathering crusts on the surface. The soil is mainly of Udic Ferralisols, with parts of mountain areas covered by Peruelic Ferrallisols and Gleysol-Paddy soils. Annual mean temperature and precipitation is 21.6℃ and 2188mm, respectively. The vegetation is southern subtropical evergreen broad-leaved forest, with about 70% of forest coverage. The river water is clear at the usual time due to the low soil erosion rate within the basin, and is relatively turbid only during the bursting flood periods. The averaged annual discharge is 3.82×10^9m^3 from 1954 to 2009, with 83.3% of which was discharged from April to September. A dam was built up and impounded in March 2008 at the lower reaches of the river, which led to a backwater section extended uP to 22km. The Qilinzui Hydrological Station （QLZ： 23°20.734′N, 113°50.399′E; 6m a.s.l.） controls 91% of the catchment area and located at the backwater section. Water samples were monthly collected at the QLZ section from December 2008 to January 2010. Water samples were also collected in July 2009 （flood season） and January 2010 （dry season） at other 23 sections on the mainstream or its tributaries. The analyzed water physical-chemical parameters include ： the total alkalinity, temperature, pH, electrical conductivity, the concentrations of DOC, POC and chlorophyll-a, and other ions. The partial pressure of CO2 of the surface water was calculated using the CO2SYS program using measured parameters. In the flooding season, a flushing effect by rainfall enhanced the contribution of allocnmonous DOC to the riverine carbon