Abstract: Aha Lake and Hongfeng Lake are two adjacent lakes on the Yunnan-Guizhou Plateau, the sedimentary environments of which are different. The sedimentary environment of Aha Lake is weakly oxidizing to reducing whereas that of Hongfeng Lake is oxidizing. To compare the enrichment, migration, and transformation characteristics of heavy metals in lakes with different sedimentary environments, contents and vertical distributions of heavy metals in sediments as well as pore waters were investigated in Aha Lake and Hongfeng Lake. The results showed that contents of Co, Ni and Zn were relatively high with moderate to heavy pollution levels in the sediments of Aha Lake. For Hongfeng Lake, while the contents of As and Zn were relatively high,  other heavy metals were unpolluted or slightly polluted. The characteristics of the cycling of Fe and Mn in two lakes were significantly different. In contrast to that in Hongfeng Lake, Fe and Mn cycling was extremely intense and the reduction zoning was more distinct in the sediments of Aha Lake, due to higher Fe, Mn, and S contents and Mn/Fe ratio. Based on those findings, we constructed a conceptual model of early diagenesis of Fe and Mn cycling process in the sediments of Aha Lake and Hongfeng Lake. Following terrigenous correction and correlation analysis, results showed that the cycling of Fe and Mn played an important role on the distributions, migrations and transformations of heavy metals. The migrations and transformations of Co, Ni, Zn and As were mainly influenced by Mn cycling, while that of Cu was mainly influenced by Fe cycling in Aha Lake. In contrast, the migrations and transformations of Co, Ni, Cu, Zn, Cr, As and Pb were influenced by Fe cycling in Hongfeng Lake.

Key words: coastal wetland, decomposition process, three-dimensional fluorescence spectroscopy characteristics, litter, soil labile organic carbon