The geochemistry of beryllium-7 in Chesapeake Bay

Abstract

The dissolved and particulate activities of 7Be in surface and deep water samples from four stations in the main stem of Chesapeake Bay were determined seven times between April, 1986 and April, 1987. Total water column concentrations ranged from < 0·05 to 3·86 dpm l −1, with an average of 0·50 dpm l −1. Batch adsorption experiments indicated a strong affinity of Be for Chesapeake Bay seston, but 7Be in the Bay was predominantly in the dissolved phase. Particulate 7Be activities reached 150 dpm g −1, but averaged 18 dpm g −1, suggesting that rapid variations in the supply of both 7Be and suspended particulates rarely allowed equilibrium partitioning of 7Be between the dissolved and particulate phases. A 7Be budget for Chesapeake Bay indicated that atmospheric deposition was always the dominant source of 7Be in the Bay. Generally, ≥ 95% of the 7Be delivered to the Bay was retained by it. Most (usually > 80%) of the 7Be in Chesapeake Bay at any time was found in the sediments.