Geochemistry and deposition of ⁷Be in river‐estuarine and coastal waters

Abstract

The atmospheric flux of cosmogenic ?Be (53.3-day half-life) and the mode of ?Be deposition in riverestuarine and coastal environments have been examined. The atmospheric flux of ?Be commonly supports inventories ranging from 1.0 to 2.0 pCi/cm 2 (1 pCi = 0.037 Bq). Beryllium 7 concentrations in water phase samples, collected across salinity gradients in several estuaries along the eastern coastline of the United States, range from 0.03 to 0.53 pCi/L and primarily reflect variations in ?Be supply and sorption kinetics. The major process controlling the concentration of ?Be on estuarine suspended particles appears to be the length of time that these particles remain in the water column. Field particle-towater distribution coefficients for ?Be have a median value of about 4 x 10 '• but range over an order of magnitude reflecting short-term variations in 7Be input, particle dynamics, and particulate iron content rather than equilibrium sorption-desorption responses to changes in water salinity or particle type.Residence times of 7Be in the water column range from a few days in estuarine areas of rapid fine-particle deposition, to several weeks in high-energy enviornments where pronounced sediment resuspension reintroduces deposited 7Be back into the water column. Inventories of ?Be in sediments range-from nondetectable to 3.3 pCi/cm 2, with the highest inventories in areas where fine particles are accumulating rapidly. Such sites are also major repositories for other particle-reactive substances. A ?Be budget for the James estuary indicates that less than 5% of the expected ?Be input is in the water column and that the short-term estuarine trapping efficiency for atmospherically derived ?Be is somewhere between 50 and 100%. the total (wet + dry) atmospheric flux of ?Be commonly supports inventories ranging from 1.0 to 2.0 pCi/cm 2 [Young and Silker, 1974; Matsunami et al., 1979; Crecelius, 1981; Robbins and Eadie, 1982; Saleh and Kuroda, 1982; Todd, 1984; Olsen et al., 1985-]. The highest inventories generally occur in the spring, when mid-latitude folding of the tropopause enhances stratospheric-tropospheric exchange, and the lowest inventories occur during periods of minimum precipitation, generally in late summer and early tall. Upon contact with "acidic" rainwater, ?Be appears to be solubilized and Be 2 + is probably the predominant species [Olsen et al., 1985]. Once deposited as a constituent of rainwater, ?Be is quickly sorbed by above-ground vegetation [Russell et al., 1981] or soil particles [Brown et al., 1981; Lundberg et al., 1983; Monaghan et al., 1983; Pavich et al., 1984] in terrestrial environments, but may remain in solution in oceanic surface waters because of the lack of suspended material [Young and Silker, 1974; Bloom and Crecelius, 1983]. The potential of 7Be as a useful tool for examining geochemical and sedimentological processes in estuarine and coastal areas (i.e., transitional zones between terrestrial and oceanic environments) has only recently been investigated [Krishnaswami et al., 1980; A...

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