Sediment-water column exchanges of nutrients and oxygen in the tidal James and Appomattox Rivers

Fluxes between the sediments and overlying water of ammonium, nitrate, total phosphorus, ortho phosphorus, and dissolved oxygen have been measured in the tidal James and Appomattox Rivers, Va. A total of 68 nutrient flux measures, 203 oxygen flux measures, and 18 control measures were collected in the summer months, 1983 and 1984. Ammonium is predominantly released from the sediments at a mean rate of 9.82 mg/m /hr. Nitrate is predominantly taken up by the sediments at a mean rate of 1.53 mg/m /hr. Total phosphorus is taken up by the sediments at a mean rate of 1.67 mg/m /hr. Ortho phosphorus may be taken up or released. Mean flux is an uptake of 0.75 mg/m /hr. Dissolved oxygen is taken up at a mean rate of 44 mg/m /hr. The primary implication of this st udy for management is that the occurrence and rate of nitrification in the water column are obscured by the simultaneous sediment release of ammonium and uptake of nitrate. It is recommended that nitrification rates in an existing water-quality model of the James River be recalibrated following inclusion of the benthic nitrogen fluxes

Two-dimensional, intratidal model study of salinity intrusion structure and motion in partially-mixed estuaries (Virginia)

A two-dimensional, longitudinal-vertical model for partially-mixed estuaries has been developed. The model provides intratidal predictions of surface level, velocity, and salinity through a semi-implicit finite-difference solution to the continuity and momentum equations and an explicit finite-difference solution to the salinity equation. The model was verified through comparison with analytical solutions, laboratory data, and prototype data. Following verification, the model was used to simulate the destratification-stratification cycle which occurs in the James River Estuary, Virginia, coincident with the spring-neap tidal cycle. In a second application to the James, a simulation of the movement of the salinity intrusion following a storm-generated freshwater flow pulse was conducted. Investigations were conducted into the reaction of a hypothetical estuary to step-like and pulse-like alterations in wind stress, tide range, boundary conditions and flow. It was noted that the reaction time-scale of the estuary was much longer than the time-scale of alterations in the forcing functions. Thus, in prototype estuaries in which forcing functions are periodic and/or randomly superimposed, truly steady-state conditions are never attained

Effect of temperature and dissolved oxygen on sediment-water nutrient flux

A series of experiments was conducted in order to determine the influence of water-column temperature and dissolved oxygen on sediment-water nutrient flux. Three nutrients were considered: ammoniurn nitrogen, nitrate nitrogen, and ortho phosphorus. Results of the experiments indicated that nutrient concentration in the overlying water had to be considered, as well as temperature and dissolved oxygen, as an independent variable which affected sediment-water nutrient flux

Sediment oxygen demand in Hunting Creek and the Potomac River

Sediment oxygen demand measures were conducted in Hunting Creek during the period June 17 to August 19, 1986