Most aquatic organisms require· oxygen to survive and consequently, the dissolved oxygen (DO) content of the water is one of the most important measures of water quality. Sources of oxygen are the atmosphere and photosynthesis. Oxygen is consumed by plants and animals during respiration and by microorganisms that decompose organic matter. The more sources and sinks of oxygen, the more difficult it is to understand and predict the oxygen dynamics of a river system. Grossly polluted systems turn out to be quite simple, because the pollutant source dominates. Natural, unimpacted systems often show a balance between a number of sources and sinks and therefore are much more complex. The rivers of the Eastern Shore of Virginia typify this latter case. The Machipongo River, including its tributary Parting Creek, drains mostly agricultural land and forest. The river has extensive fringe marshes and tidal flats which are exposed at low water. A large mechanized clam processing facility located at Willis Wharf, Virginia also discharged wastewaters to Parting Creek. The organic loadings in these wastewaters have varied over time as processing techniques and production levels changed. Mathematical models are very useful tools that allow water quality managers to predict the environmental response to various actions, such as an increase in pollutant loads when a new facility begins discharging wastewaters or a decrease in pollutant loads when treatment levels are increased. Models can be only as good as the field data upon which they are based. When a system is complex, the data set must be comprehensive, and often extensive in time, so that there is sufficient information to allow the effects of all major factors to be determined. For the Machipongo River, such a field effort would be very expensive. Consequently, studies have been more limited in scope and designed to examine one factor only, namely the effects of the clam processing wastewaters. In the spring of 1989, a field study was undertaken to see if water quality differed between Parting Creek, which received the clam wastes, and the Machipongo River, which had no comparable wastewater loading. In the fall of 1990, another study was conducted to see whether conditions had changed in response to waste load reductions at the clam processing plant. Subsequently, the clam processing plant was closed, so the waste loading to Parting Creek was eliminated. This report describes the data collected during the spring of 1992, when there was no discharge from the plant. At a later date, these data will be compared with those from prior years to determine what, if any, change in water quality has resulted from the elimination of this point source of organic wastes
