| Controlled ecosystems (microcosms) provided a means for the detailed study of transport processes between bodies of water and underlying sediments through intentional additions of radiotracers followed by measurements of their distribution in time and space. The MERL (Marine Ecosystem Research Laboratory) microcosm tanks, located in Narragansett, RI, were used for this purpose.; Two pulse additions of up to 15 gamma-emitting radiotracers to the water column of a MERL tank were carried out, one in winter (2(DEGREES)C) and the second in summer (24(DEGREES)C). The migration of ('22)Na, measured the movement of pore-water. Radioactively tagged plastic particles elucidated the rate of particle transfer in the sediments. ('7)Be, ('59)Fe, ('113)Sn, ('203)Hg, ('233)Pa, ('51)Cr mirrored the particle tracer. ('65)Zn, ('60)Co, and ('109)Cd, exhibited more mobility. ('133)Ba, ('125)Sb, ('54)Mn and ('134)Cs acted most like ('22)Na, moving extensively with pore-waters. Correlations between core inventories of the different elements with that of the particle microspheres suggested that the more soluble elements entered the sediments more uniformly than the "particle-reactive" elements.; A new laboratory method was designed to measure sediment tortuousity, and the diffusivity and distribution coefficient of ('22)Na and other soluble radiotracers. Application of these transport parameters to MERL sediment cores showed a 2.5-fold increase over ionic diffusion owing to bioturbation in winter, and 4-12 times faster than ionic diffusion in the top 5-6cm in summer.; An experiment was designed to determine the significance of zooplankton filtering for acclerating the transfer of elements from the wate column to the sediments in the summer. A zooplankton cage was built to capture copepods and their fecal pellets as they fed on the radioactively-labelled seawater. Results demontrated that grazing accounts for < 3% of the total tracer deposition. It was concluded that benthic processes rather than planktonic processes promote mass flux in the warm months. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI... |
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