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This study aimed to clarify the seasonal variations and properties of refractory organic mat ter within the dissolved organic matter fraction in Lake Kojima, located in Okayama, western Japan, and in its major inflowing sources: the Kurashiki River, the Sasagase River, paddy field runoff, and ef f luent from a sewage treatment plant. In all surface lake water, river water, and paddy runoff samples, DOC concentrations exhibited clear seasonal patterns—higher in summer and lower in winter—with 56–80% of refractory DOC. During the rice-field plowing season, most of the refractory DOC in the lake originated from river inflows. In contrast, during summer, approximately 1.2 mg L-¹ of refractory DOC appeared to be produced within the lake. In the effluent from the sewage treatment plant, refrac tory DOC accounted for 85–86% of total DOC—significantly higher than the approximately 80% ob served at the lake center—indicating that treated wastewater is also an important source of refractory organic matter. Fluorescence EEM analysis further revealed that protein-like peaks were associated with labile compounds, whereas humic-like peaks represented refractory fractions.
Research papers (academic journals)
