Changes in dissolved organic matter chemistry of plateau lakes along gradients of human activity intensity in Yunnan Province, China.

Plateau lake systems are highly sensitive indicators and amplifiers of global climate change, while human activities are emerging as a growing threat to their ecological health and carbon cycling. As the dominant organic carbon pool, dissolved organic matter (DOM) plays essential roles in lake biogeochemical cycles and ecosystem health. However, the impacts of human activities along intensity gradients on DOM chemistry in plateau lakes remain unknown. Here we quantified human activity intensity (HAI) of nine plateau lakes in Yunnan Province (China) based on land use/cover data, coupled with DOM characterization using spectroscopic techniques and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to address these issues. The results showed that the pronounced spatial heterogeneity in the quantity and quality of DOM, and it was highly associated with HAI values across the nine plateau lakes. With increasing HAI values, the dissolved organic carbon, absorption coefficients at 355 nm, DOM aromaticity, humification degree, abundances of fluorescent components, and heteroatom-bearing compounds all significantly increased in plateau lakes. Anthropogenic-induced nutrient inputs along with allochthonous DOM, shifted the source of autochthonous DOM from submerged plant degradation to algal and/or phytoplankton metabolisms. This shift further significantly elevated the proportions of heteroatom molecules in DOM, and consequently complicated the organic matter pool in plateau lakes. We conclude that intensified human activities could significantly alter DOM quantity and quality, and potentially affect its biogeochemical function in plateau lake systems.