Spatiotemporal Variation of Water Chemistry in Meadow Run

Meadow Run is one of the most acidified streams in Shenandoah National Park, making it a prime target for intervention to accelerate its recovery from historic acid deposition. Meadow Run has exhibited persistent acidity with low pH and acid neutralizing capacity (ANC) values as recorded by the Shenandoah Watershed Study (SWAS) from 1987 to present. To remediate this acidification, liming or the spreading of limestone sand across Meadow Run by the National Park Service (NPS) is scheduled for the winter of 2025. This study is intended to provide a thorough analysis of the stream chemistry before the liming.
In this study, the influences of the two different types of siliclastic bedrock underlying the Meadow Run watershed were assessed spatially and temporally. A spatial influence was found as areas containing a larger percentage of the Antietam Formation possessed lower ANC pH, and base cation measurements than areas with a larger percentage of the Harpers Formation. However, with the exception of sulfate, the temporal recovery from acidification did not appear to be influenced by the bedrock geology as there were no consistent patterns for variations in ANC, pH, and base cations from 1994 to 2023. This study also investigated the spatial and temporal relationship between dissolved organic carbon (DOC) and pH as some limed watersheds have reported increases in DOC resulting from increases in pH. A statistically significant relationship was not found between pH and DOC spatially or temporally. However, this is likely due to minimal natural variation of pH and the influence of DOC by other temporal factors (e.g. hydrology) and spatial factors (e.g. soil characteristics). After the liming, this relationship will continue to be studied to determine if larger increases in pH with other factors held constant directly affect the DOC.