MODERN CL-36 DEPOSITION IN SOUTHERN MARYLAND, USA

Monthly wet precipitation samples were collected at the Elms Environmental Education Center in St. Mary's County in southern Maryland from February 1991 to January 1993 and analyzed for Cl-36. The analyses indicate that Cl-36 wet deposition undergoes seasonal variations, reaching a maximum in March/April. This pattern is well established for other stratospheric tracers such as Pu, Be-7, Be-10 and ozone, and reflects seasonal variations in stratospheric-tropospheric mixing. The mean wet deposition Cl-36 flux was 3.86 +/- 0.54 (x 10(-3)) atoms/cm2 s. Bulk precipitation samples were also collected at the site during the sampling period, and these data are compared to the wet-only data. The mean bulk deposition flux was 5.85 +/- 0.78 (x 10(-3)) atoms/cm2s. Dry deposition accounts for approximately 25% of the total Cl-36 deposition. Data from this study are compared with groundwater Cl-36 data from the Aquia Aquifer in southern Maryland, and it is concluded that modem deposition does not account for the relatively high Cl-36 concentrations found in the Aquia.