NAWQA: Study Components and Data

Streams

Stream sampling as part of the NAWQA program in the PODL is designed to assess spatial, seasonal, and temporal variability in surface-water quality. Although tidal waters are common throughout the study area, sampling is limited to free-flowing, non-tidal streams and rivers.

Regional synoptic surveys of water quality in low-order streams have been conducted in the Piedmont, Valley and Ridge, and Delmarva Coastal Plain. These studies were generally done under base-flow conditions in the late summer; a few were also sampled in the spring. A synoptic survey of water quality in major tributaries of the Potomac River Basin was also conducted during spring base flow in 1994. Data from these surveys provide a measurement of the quality of ground water discharging to streams of the study area, and thereby supplement and provide a context for information from regional ground-water studies.

A reconnaissance survey of selected PODL streams was recently conducted to evaluate the occurrence and distribution of mercury in game fish.

Seasonal and temporal variability in surface-water quality is evaluated through repetitive sampling of selected streams ("Trends Sites"). Streams of various sizes in a variety of land-use and geologic settings are sampled on a fixed-interval that varies from weekly to bimonthly. Some additional samples have also been collected during periods of unusually high flow. Sampling sites on selected streams generally coincide with locations of stream gages that provide continuous stream-flow measurements. Although the network of NAWQA streams sampled to evaluate temporal and seasonal trends has evolved considerably since it was established in the early 1990s, some streams in the Potomac River Basin have been sampled repetitively for nutrients, pesticides, and other chemicals since 1993.