ABSTRACT Conceptual model of dissolved oxygen dynamics in a river. Phytoplankton, periphyton, and macrophytes are shown as primary producers with internal biomass transfers and losses. Dissolved oxygen is increased by photosynthesis and reaeration and decreased by respiration, nitrification, carbonaceous biochemical oxygen demand (cBOD), and sediment oxygen demand (SOD). Dissolved oxygen (DO) is critical to aquatic life, and its concentration is one of the most important indicators of water quality. Therefore, reliable estimates of DO concentrations are essential. DO dynamics arise from interacting physical and biogeochemical processes that are strongly modulated by temperature and salinity; here, we developed a process-based model to predict DO concentrations that explicitly incorporates both drivers. Primary producers were accounted for as three functional groups, i.e., phytoplankton, periphyton, and macrophytes. The local sensitivity analysis indicated that the reaeration coefficient was the most important variable affecting the DO dynamics. We calibrated and validated the model using field measurements from a large central German stream for the period of January 2014 to December 2015 and January 2016 to December 2018, respectively. The DO concentration was well predicted (Nash–Sutcliffe efficiency above 0.75). The model also reflected seasonal patterns of phytoplankton concentrations. However, the surge during summer periods in 2017 and 2018 was not captured by the model. Calibration relied solely on DO and phytoplankton observations. Periphyton and macrophytes were included as additional process-based state variables; however, corresponding field data were unavailable for calibration or validation. Further subdivision of algal groups may improve model performance.
Farias et al. (Wed,) studied this question.