It has recently been reported that plateau lakes have been seriously polluted by organic matter, however, the sources of this organic matter and their relative contributions remain unknown. In this study, to determine the sources and composition of the organic matter in the Hulun Lake basin during the spring-thaw period, a total of twenty-three sampling sites were investigated. Results showed high levels of organic matter pollution in the surface water of Hulun Lake, with an average COD values of 119.35 mg L-1. Organic matter came from natural sources as well as a variety of anthropogenic activities. The direct sources included urbanization, industrial and residential wastewater discharge, and emission from burning fossile fuels. A large indirect source was organic matter from tumbleweed decomposition, which had increased due to desertification caused by overgrazing. The principal component analysis showed that organic matter from Hulun lake shared composition and sources with the upstream sections of the natural tributaries and the downstream section of the artificial tributary. The artificial inflow river contributed more organic matter than the other tributaries. Notably, a large portion of organic matter in Hulun Lake came from decomposing tumbleweed concentrated in the downstream section of one of the natural rivers. New indirect consequences of human activities must be factored into the rule and regulations that protect plateau lake ecosystems alongside the direct effects of established human activities.
Keywords: Anthropogenic activity; Organic matter source; Plateau lake; Spring-thaw period.