How does colored dissolved organic matter (CDOM) influence the
distribution and intensity of hypoxia in coastal oceans?
Abstract
Excessive nutrient loading is a well-established driver of hypoxia in
aquatic ecosystems. However, recent limnological research has
illuminated the role of Chromophoric Dissolved Organic Matter (CDOM) in
exacerbating hypoxic conditions, particularly in freshwater lakes. In
coastal ocean environments, the influence of CDOM on hypoxia remains an
underexplored area of investigation. This study seeks to elucidate the
intricate relationship between CDOM and hypoxia by employing a
nitrogen-based model within the context of Chesapeake Bay, a large
estuary with unique characteristics including salinity stratification
and the localization of hypoxia/anoxia in a 30-meter-deep channel
aligned with the estuary’s primary stem. Our findings indicate that the
impact of CDOM on nutrient dynamics and productivity varies
significantly across different regions of Chesapeake Bay. In the upper
Bay, the removal of CDOM reduces light limitation, thus promoting
increased productivity, resulting in the generation of more detritus and
burial, which, in turn, contributes to elevated levels of hypoxia. As we
transition to the middle and lower Bay, the removal of CDOM can cause a
decline in integrated primary productivity due to nutrient uptake in the
upper Bay. This decrease in productivity is associated with reduced
burial and denitrification, ultimately leading to a decrease in hypoxia
levels. Streamflow modulates this impact. The time integral of the
hypoxic volume during low-flow years is particularly sensitive to CDOM
removal, while in high-flow years, it is relatively unchanged. This
research underscores the necessity for a comprehensive understanding of
the intricate interactions between CDOM and hypoxia in coastal
ecosystems.