Transport and Fate of Particulate Organic Nitrogen in Chesapeake Bay: a Numerical Study

In Chesapeake Bay, substantial quantities of organic matter are produced during the spring bloom, which contributes to severe chronic bottom oxygen depletion during the summertime. However, the details of this transport in the estuarine system under realistic forcing is still unclear. In this research, a three-dimensional coupled physical-biogeochemical model has been used to investigate the production, transport and fate of organic matter in Chesapeake Bay. Analysis of a control volume in the deep channel reveals that the sinking flux of fast-sinking particulate organic nitrogen (PON) into the deep channel is comparable to the horizontal advective transport in contributing in the accumulation of PON in the thalweg, both on the scale of 10(6) mol nitrogen/day during springtime. The model analysis also reveals a pronounced east to west transport of PON during the springtime and a tendency to export mass from the eastern shore to the deep channel and from the deep channel to the western shore of the Chesapeake Bay, and also a convergence of mass transport on the western shore. This transport pattern is consistent with the springtime lateral estuarine circulation in Chesapeake Bay that arises due to the asymmetry of the flood-neap tidal cycle. In addition, the model reveals that seasonal variations in wind alter the magnitude and distribution of organic matter flux in the along channel and cross channel direction, with northerly winds during the springtime favoring more northward organic matter transport and more organic matter accumulation in the deep channel. Numerical experiments suggest that with enhanced northerly winds, bottom PON accumulation increases to as much as 3.25 x 10(6) mol nitrogen/day in April. However, the lateral net flux direction and pattern remain the same.

Automated summary

The study reveals different transport patterns of organic matter in both lateral and longitudinal directions within Chesapeake Bay during springtime, and shows that wind variations can significantly impact the magnitude and distribution of organic matter flux.