HISTORY OF CRITICAL ZONE RESEARCH AT CATOCTIN MOUNTAIN, MARYLAND

Catoctin Mountain forms part of the Blue Ridge Physiographic Province in north-central Maryland. The mountain is a metabasaltic anticline flanked by quartzite-rich metasediments, representing a pronounced environmental gradient of lithologic chemical reactivity. Small, headwater, forested, relatively undisturbed watersheds drain the mountain and eventually contribute to Chesapeake Bay. As such, watersheds on Catoctin Mountain provide an ideal setting for study of Critical Zone transfers of mass and energy at Earth’s surface using the small watershed mass-balance approach. Owen Bricker, formerly of the U.S. Geological Survey, started Critical Zone research in small, forested watersheds underlain by the metabasalt in 1982. He and his research team evaluated the effects of acidic deposition on Catoctin Mountain by establishing stream-gaging stations and sampling precipitation and stream water weekly in streams across the lithologic gradient. Using precipitation and stream-water chemistry, the Catoctin team published mass balances for the metabasaltic watersheds including calculated mineral-weathering rates. The team determined the strong control of hydrologic flow paths on the seasonality of stream-water chemistry in the metabasaltic watersheds. Using stable isotopes in addition to groundwater, soil-water, and stream-water chemistry, the team elucidated the hydrologic flow paths in the watersheds underlain by the quartizite-rich metasediments during both stormflow and base flow. Most recently, the team has contributed quantitative geochemical mass-balance modeling in both the metabasaltic and the quartzite-rich metasedimentary watersheds, adding a much needed biotic uptake term to the quantification. In addition, the team has investigated the effects of road salt on the geochemical mass balances of the metabasaltic watersheds and quantified atmospheric CO₂ consumption attributable to the weathering of Ca-Mg-silicate phases. Although Owen Bricker is deceased, his legacy of Critical Zone research in small, forested watersheds, particularly at Catoctin Mountain, remains.