. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Waquoit Bay (B). Distance (m)(c) * 0 4 8 12 ** -~ 0 E a a a Figure 1. Lucullan of It tii/uoir Bay. Massachusetts, and our sampling site during the summer of 2003. Wai/noil Ba\ is located activity, a continuous measurement at radan-222. iiiul a transect a/ four depth profiles oriented perpendicular lo the heach u-ere used to quantify SGD (B, A = --''Ra, O = 222Rn, * - ** = transect of 4 depth profiles). A verticil/ cross .sectiim of' xroiintlwater revealed a sharp increase in salinity 111 the freshwater-saltwater interface tC
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Waquoit Bay (B). Distance (m)(c) * 0 4 8 12 ** -~ 0 E a a a Figure 1. Lucullan of It tii/uoir Bay. Massachusetts, and our sampling site during the summer of 2003. Wai/noil Ba\ is located activity, a continuous measurement at radan-222. iiiul a transect a/ four depth profiles oriented perpendicular lo the heach u-ere used to quantify SGD (B, A = --''Ra, O = 222Rn, * - ** = transect of 4 depth profiles). A verticil/ cross .sectiim of' xroiintlwater revealed a sharp increase in salinity 111 the freshwater-saltwater interface tC. contour plot from * to **). related to ion exchange (7). The pattern we observed could be explained by an increased 22<1Ra source with increasing depth and distance from shore, a function of either higher sediment content of thorium-230 (radiogenic parent of 22(1Ra) or a decrease in the grain size of aquifer sediments. This latter scenario would result in greater sediment surface area, thereby increasing the availability of radium for desorption. However, sediment sampling at the head of Waquoit Bay is necessary to determine which of these two possi- bilities is the nmst likely explanation for the observed pattern. The pattern of groundwater 222Rn with salinity was similar to that of ~2"Ra, with ~3-fold increases in activity at salinities higher than 20 (Fig. 2a). 222Rn also displayed an increase in activity with increasing depth and distance from the berm (Fig. 2b). Because Rn is a noble gas, its distribution throughout the aquifer should be uniform, and not affected by changes in salinity. Also, because the residence time of fresh groundwater beneath the bay is several years (8), the activities of 222Rn in this zone are likely to be in equilibrium with the sediment activity of its parent isotope 22"Ra. Therefore, the higher observed activities of 222Rn in the saline portion of the aquifer must be a function of a greater 22"Ra source, which is consistent wi
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
