SWAS-VTSSS Program Overview
The SWAS-VTSSS program is a monitoring and research network focused on mountain streams in western Virginia. Most of the program's study streams maintain naturally reproducing populations of the region's native brook trout (Salvelinus fontinalis
), and most of the streams are associated with public lands, including national park, national forest, and wildlife management areas.
The objectives of the SWAS-VTSSS program are to increase understanding of factors that govern biogeochemical conditions and stressor-response relationships in forested mountain watersheds of the central Appalachian region. Progress in addressing these scientific and problem-oriented objectives has been achieved through development of a data collection network that accounts for spatial gradients, as well as temporal variation, in the chemical composition of relatively undisturbed headwater systems in the region.
The SWAS-VTSSS program is notable for the length of the continuous data record that has been obtained, including the longest-running record of stream water composition and discharge in the U.S. national park system. The SWAS component of the program, which includes streams that are sampled in Shenandoah National Park, was initiated in 1979. The VTSSS component, which extended sampling to streams in national forest and other conservation lands in western Virginia, was initiated in 1987.
SWAS-VTSSS monitoring accounts for ecological variation among the region's forested mountain watersheds with a data-collection strategy that represents: (1) spatial variation through the distribution of hydrochemical monitoring within a lithologic classification system; and (2) temporal variation through long-term data collection at fixed locations sampled at different frequencies.
The lithologic classification system includes six classes based on the physical and chemical properties of bedrock formations in the region. Acid neutralizing capacity (ANC) and concentrations of related acid-base constituents in stream waters, as well as other biotic and abiotic properties of watersheds, differ among the lithologic classes. There is, for example, a strong association between lithologic class, ANC, and numbers of fish species in the streams of Shenandoah National Park. Strong associations have also been documented between lithology and important forest properties, including the base status of soils and both the distribution and nutrient content of vegetation.
The SWAS-VTSSS data collection framework is most-well developed in the Blue Ridge Mountains Province within Shenandoah National Park, where stream water composition data are collected seasonally at 14 sites, weekly at four sites, and every two hours during episodic high-flow conditions at three sites with continuous discharge gauging. Stream water composition data are collected on a seasonal basis at an additional 58 sites located outside of the Park, in both the Blue Ridge Mountains and Ridge and Valley Provinces.
Change within the study region's forested mountain watersheds is driven by both chronic and episodic factors.
Responses to multi-year changes in acidic deposition have been reflected in long-term trends in concentrations of sulfate, ANC, and other acid-base constituents of streams in the network. Expectations for southeastern watersheds with soils that retain sulfur, for example, were confirmed by the lack of immediate improvement in stream water quality following reductions in acidic deposition mandated by the Clean Air Act.
The acid-base chemistry of streams in the network also varies seasonally and on shorter time scales. Weekly and higher-frequency automated stream water sampling during periods of high runoff have supported the study of episodically more-acidic conditions, including the study of fish sensitivity with in-stream bioassays and development of models to predict severity and recurrence intervals.
Change also occurs on a transient basis. The gypsy moth infestation in the early 1990s, for example, resulted in several years of forest defoliation throughout much of the network. The effect of this transient disturbance on watershed nutrient cycling was dramatically increased nitrate concentrations in stream waters for a number of years following the defoliation.
By accounting for significant spatial gradients and temporal patterns in the region, the SWAS-VTSSS hydrochemical data collection program provides a basis for both observing and interpreting watershed-scale change, as well as an informed foundation for process-oriented research. Monitoring data and research findings obtained through the SWAS-VTSSS program have contributed to increased scientific understanding, as well as to policy formulation and implementation.