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

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

Water Quality in a Small Tidal Creek: Parker Creek, Virginia

Parker Creek is a branched tidal creek located on the Eastern Shore of Virginia. In its southern branch, the creek receives waste inputs from a poultry processing plant. A study has been conducted to determine the effects of these inputs and to formulate a mathematical model of the creek system suitable for water quality planning. The model and field studies show the creek may be divided into two zones, an upstream zone dominated by freshwater flows and waste inputs, and a downstream zone dominated by conditions in adjacent Metomkin Bay. In the upstream zone of the waste-receiving branch, conditions of elevated nutrient and depressed dissolved oxygen concentrations exist. In the downstream zone, conditions are close to natural. For purposes of comparison, surveys were conducted in three similar non-impacted tidal creeks and in Metornkin Bay. From a planning standpoint, the most significant result of these surveys is that violations of minimum dissolved oxygen standards may occur as a natural condition in tidal creeks

Model integration and the role of data

a b s t r a c t Model integration is becoming increasingly important as our impacts on the environment become more severe and the systems we analyze become more complex. There are numerous attempts to make different models work in concert. However model integration usually treats models as software components only, ignoring the evolving nature of models and their constant modification and re-calibration to better represent reality. As a result, the changes that used to impact only contained models of subsystems, now propagate throughout the integrated system, across multiple model components. This makes it harder to keep the overall complexity under control and, in a way, defeats the purpose of modularity, where efficiency is supposed to be gained from independent development of modules. We argue that data that are available for module calibration can serve as an intermediate linkage tool, sitting between modules and providing a module-independent baseline, which is then adjusted when scenarios are to be run. In this case, it is not the model output that is directed into the next model. Rather, model output is presented as a variation around the baseline trajectory, and it is this variation that is then fed into the next module down the chain. The Chesapeake Bay Program suite of models is used to illustrate these problems and the possible remedy. Published by Elsevier Ltd