Science Serving Maryland's Coasts

Kelly Kearney, University of Miami

Class Year: 

Project Title: 

A Model for Nutrient Pathways in the Choptank River


One of the most predominant problems facing the Chesapeake Bay and its tributaries today is that of excess nutrient loading, which can lead to several detrimental ecological effects. However, although the results of high nutrient concentration have been studied in detail, few quantitative studies on nutrient sources have been conducted. This paper concentrates on the development of a one-dimensional advection-diffusion model for the Choptank River, the largest Eastern Shore Chesapeake Bay tributary. The model is based on the salt balance equation:

∂(σs)   =   –   ∂(Rsσ)   +   ( σK   ∂sσ )

∂t ∂x ∂x ∂x

  is the cross-sectional area of the river
  is the average salinity over a cross section
  is the position downriver along a central axis
  is the streamflow over a cross-section at a specific time, and
  is a diffusion coefficient

Using salinity data collected from the CISNet cruises between 1999 and 2001, the diffusion coefficient K was calculated once with time dependence, and once without. Currently, it does not appear that time-dependence makes a significant contribution to the diffusion coefficient, but it may play a larger role in the final model. The preliminary results of the model show that a one-dimensional model can accurately estimate salinity in a well-mixed sub-estuary such as the Choptank River. In order to complete this nutrient transport model, the model will need to be calibrated with the CISNet data and verified with an independent data set. A conservative tracer will then be added to the model to represent transport. Finally, a non-conservative tracer will be added to represent nutrient transport.