| Lake ecosystems are strongly linked to their terrestrial surroundings by material and energy fluxes across ecosystem boundaries. The terrestrial organic carbon input is an important part of organic carbon source in lakes, and plays a key role in maintaining material and energy circulation in lake ecosystems. Organic carbon in rivers, mainly including particulate organic carbon(POC) and dissolved organic carbon(DOC), is a mixture of terrestrial plant debris and soil organic matter. Revealing the sources, spatial distribution and control factors of riverine organic carbon not only helps to investigete the whole picture of terrigenous organic carbon cycle, and provide the basic data for the study of organic carbon cycle in lakes, but also lays a solid foundation for understanding the carbon cycle and planning reasonable eutrophication prevention and control strategies. In this paper, the δ13C and concentrations of DOC and POC of the inflow waters of Fuxian lake and Dianchi lake were determined to investigate the spatial distribution, source and control factors of the organic carbon. The main conclusions were as follows:(1) The seasonal variation of DOC concentrations in rivers of Fuxian Lake was obvious,while the the POC concentrations changed little in both seasons. The DOC and POC concentrations ranged from 2.79 to 38.02mg/L and 1.79 to 5.41mg/L, and from 0.22 to2.68mg/L and 0.10 to 2.75mg/L in winter and summer, respectively. The emissions of waste water from agriculture and living of the drainage basin mainly controlled the distribution of DOC and POC concentrations in these rivers.(2)The seasonal variation of δ13CDOC and δ13CPOC values was not obvious in rivers of Fuxian Lake. The δ13CDOC and δ13CPOC values ranged from-12.6‰ to-25.5‰ and-12.3‰ to-25.5‰ in winter and summer, respectively. While the δ13CPOC values ranged from-23.2‰ to-27.0‰ and-24.2‰ to-27.2‰. The DOC in rivers of Fuxian Lake was of a mixed origin of nonpoint source pollution and sewage discharge, and the POC in rivers was of a mixed origin of soil erosion and plant fragments input.(3)The seasonal variation of DOC and POC concentrations in rivers of Dianchi Lake changed little in both seasons. The DOC and POC concentrations ranged from 1.59 to7.11mg/L and 2.73 to 5.14mg/L, and from 0.13 to 0.83mg/L and 0.20 to 1.09mg/L in winter and summer, respectively. Urban construction, organic wastewater of industry and sewage discharge were the main control factors to make DOC and POC concentrations in difference.(4)The seasonal variation of δ13CDOC values of Dianchi Lake was not obvious, and ranged from-20.1‰ to-35.8‰ and-20.6‰ to-33.3‰ in winter and summer respectively.While the δ13CPOC values ranged from-17.5‰ to-29.0‰ and-24.4‰ to-30.5‰ respectively,more positive in winter than in summer. The DOC in rivers was of a mixed origin of industrial wastewater and sewage discharge, or phytoplankton photosynthesis. And the POC in rivers mainly derived from autogenous organic matter and C3 plant fragments input, and the C4 plant debris input might be a major source for some rivers.(5)The inflow rivers of Dianchi and Fuxian Lake were different. The rivers of Fuxian Lake were village farmland polluting rivers, and the DOC was of a mixed origin of nonpoint source pollution and sewage discharge,while the POC in rivers was of a mixed origin of soil erosion and plant fragments input. On the contrary, the rivers of Dianchi Lake were in high organic loading. And the DOC in rivers was of a mixed origin of industrial wastewater and sewage discharge, or phytoplankton photosynthesis. While the POC in rivers was mainly from autogenous organic matter and C3 plant fragments input. |
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