Development of Finite Segment Estuarine Total Phosphorous Flux Model

The James River Treatment Plant (JRTP), Newport News, VA situates at the mouth of the Warwick River, a partially mixed estuarine tributary of the James River.  Objectives of this study are to characterize mixing, transport and flux of total phosphorus (TP) loading from the JRTP’s effluent discharge in the estuarine cove of Warwick River, and to model subsequent system-level eutrophic response by using a Finite Segment Model (FSM) framework.

The study site was subdivided into four finite segments with two boundary conditions at each end by using the constant-volume CV approach where the area, volume, and length were estimated from GIS database by using ArcGIS and depth from NOAA and Hampton Roads Sanitation District (HRSD) data sources. Net flow rate was estimated with velocity samples measured by a current meter. In each segment, TP flux was expressed in forms of advective, diffusive/dispersive and decay transport components.  Dispersion coefficients, E and subsequent bulk dispersion coefficients, E’ were estimated from in situ salinity samplings along with tidal cycles. Resultant dispersion coefficients indicate that flux and transport in the study site is heavily influenced by dispersion as the estuary number, Eta was greater than 10.  Phosphorous concentrations were also sampled in situ.

With data, measured and calculated, were then used to develop FSM modelling framework to predict TP concentrations in the estuarine cove of Warwick River segments 1,2,3, and 4 where segment 1 receives a point source loading from the Warwick River, and segment 4 receives a point source TP effluent loading from JRTP containing. FSM modelling framework predicts TP concentrations of 0.07 mg/L, 0.05 mg/L, 0.03 mg/L and 0.02 mg/L for the segments 1.2.3 and 4, respectively, where measured spectrophotometric values of the TP samples from the same segments site were 0.081 mg/L, 0.054 mg/L, 0.05 mg/L and 0.03 mg/L for segments 1,2,3 and 4, respectively.  It is concluded that developed FSM modelling framework can be used to simulate and predict TP transport, flux and concentration in the study segments in the estuarine cove of Warwick River with varying loading conditions from JRTP treatment plant during events of accidents and malfunction. In addition, FSM modelling framework can be also applied to simulate and predict resultant TP flux response upon receiving multiple PS and NPS loadings from surrounding catchments to evaluate subsequent estuarine eutrophication potential.