Assessing Phosphorus Control in the James River Basin

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Abstract
A tidally averaged water quality model was used to study the factors limiting the phytoplanton growth in the James River Estuary in Virginia. The water quality constituents simulated by the model are CBOD, dissolved oxygen, organic nitrogen, ammonia nitrogen, nitrite plus nitrate nitrogen, organic phosphorus, inorganic phosphorus, and chlorophyll a. The kinetics of major physical, chemical, and biological processes which link these water quality constituents are modeled in each of the 50 model segments in the longitudinal direction of the upper James River estuary. Model calibration and sensitivity analyses indicate that the phytoplankton growth plays a significant role in contributing to ultimate CBOD through respiration of live phytoplankton as well as recycling of carbon from dead algal biomass. In addition, algal growth is important in balancing the dissolved oxygen budget via photosynthesis and respiration. More importantly, turbidity controls the phytoplankton growth. Nutrients (nitrogen and phosphorus) are found not to be be a key limiting factor in the upper James River Estuary under the present conditions. However, the model projection analysis indicates that significant phosphorus load reduction from municipal wastewater treatment plants would reduce phosphorus to levels that limit the phytoplankton growth and thereby control phytoplankton biomass to reasonable and manageable levels.

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