Hydrologic, chemical, and isotopic characterization of two small watersheds on Catoctin Mountain, north-central Maryland, U.S.A.

Two small (100 ha) watersheds located on Catoctin Mountain in north-central Maryland were intensively instrumented in 1990 and have been hydrologically, chemically, and isotopically monitored for 3 years. Dissolved concentrations of major ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, total AI, CI^-, NO₃^-, SO₄^2- , HCO_3^-, and SiO₂) and stable isotopic (D and ¹⁸O) values have been analyzed for most types of water (precipitation, throughfall, two depths of soil water, shallow groundwater, and streamwater) that enter, travel through, and exit each watershed. The major objectives of the study were to characterize the chemical and isotopic signatures of all aqueous components of the watersheds and to interpret the causes of the changes in chemical and isotopic compositions of streamwater during storm runoff. This paper describes selected results of the study.