How can light absorption by CDOM modulate the distribution of hypoxia in Chesapeake Bay?

Excessive nutrient loading is a well-established driver of hypoxia in aquatic ecosystems. However, recent limnological research has highlighted the role of Chromophoric Dissolved Organic Matter (CDOM) in modulating hypoxic conditions, particularly in freshwater systems. In estuarine systems, this influence is less well understood. This study explores the interactions between CDOM and hypoxia in Chesapeake Bay by implementing a nitrogen-based biogeochemical model with an improved light attenuation parameterization that explicitly represents CDOM as a function of riverine refractory dissolved organic carbon (DOC). Chesapeake Bay’s estuarine structure—featuring salinity stratification and a deep axial channel—makes it an ideal testbed. We find that the removal of CDOM increases light availability and alters productivity and nutrient dynamics, with regionally distinct outcomes. In the upper Bay, CDOM removal stimulates surface productivity, increasing detritus and leading to elevated respiration and hypoxia. In contrast, in the middle and lower Bay, light-enhanced productivity shifts downward due to surface nutrient depletion, deepening oxygen productionand increasing both oxygen supply and remineralization in the deep channel.. The net effect is to reduce bottom hypoxia. These dynamics are sensitive to streamflow: the integrated hypoxic volume during dry years shows a strong response to CDOM removal, whereas in wet years, the effects are more muted. These results emphasize that CDOM, through its modulation of light and productivity depth, can either intensify or mitigate hypoxia depending on hydrographic context, highlighting the need for its explicit representation in estuarine models.