Optical measurements of dissolved organic matter as proxies for CODMn and BOD5 in plateau lakes

The presence of organic matter in lakes profoundly impacts drinking water supplies, yet treatment processes involving coagulants and disinfectants can yield carcinogenic disinfection by-products. Traditional assessments of organic matter, such as chemical oxygen demand (COD_Mn) and biochemical oxygen demand (BOD₅), are often time-consuming. Alternatively, optical measurements of dissolved organic matter (DOM) offer a rapid and reliable means of obtaining organic matter composition data. Here we employed DOM optical measurements in conjunction with parallel factor analysis to scrutinize COD_Mn and BOD₅ variability. Validation was performed using an independent dataset encompassing six lakes on the Yungui Plateau from 2014 to 2016 (n = 256). Leveraging multiple linear regressions (MLRs) applied to DOM absorbance at 254 nm (a₂₅₄) and fluorescence components C1–C5, we successfully traced COD_Mn and BOD₅ variations across the entire plateau (68 lakes, n = 271, R² > 0.8, P < 0.0001). Notably, DOM optical indices yielded superior estimates (higher R²) of COD_Mn and BOD₅ during the rainy season compared to the dry season and demonstrated increased accuracy (R² > 0.9) in mesotrophic lakes compared to oligotrophic and eutrophic lakes. This study underscores the utility of MLR-based DOM indices for inferring COD_Mn and BOD₅ variability in plateau lakes and highlights the potential of integrating in situ and remote sensing platforms for water pollution early warning.