Abstract: Extensive tidal studies in island wells and the lagoon at Enewetak Atoll have shown that island ground water dynamics are controlled by a layered aquifer system. The surface aquifer of unconsolidated Holocene material extends to a depth of approximately 15 m, and has a hydraulic conductivity K = 60 m/day. From 15 to 60 m (approximate lagoon depth) the reef structure consists of successive layers of altered Pleistocene materials, with bulk permeability substantially higher than that of the surface aquifer. Because of wave set-up over the windward reef and the limited pass area for outflow at the south end of the atoll, lagoon tides rise in phase with the ocean tides but fall later than the ocean water level. This results in a net lagoon-to-ocean head which can act as the driving force for outflow through the permeable Pleistocene aquifer. fresh water, This model suggests that nutrients or radioactive contaminants found in island ground water or reef interstitial water may be discharged primarily into the ocean rather than the lagoon. Atoll island fresh water resources are controlled by recharge, seawater dilution due to vertical tidal mixing between the surface and deeper aquifers, and by loss due to entrainment by the outflowing water in the deeper aquifers. Estimated tagoon-ot-ocean transit times through the deep aquifer are on the order of a few years, which corresponds well to the freshwater residence time. estimates based on inventory and recharge. Islands in close proximity to reef channels have more fresh ground water than others, which is consistent with a locally reduced hydraulic gradient and slower flow through the Pleistocene aquifers.; Major Descriptors: *ENIWETOK -- HYDROLOGY; *GROUND WATER -- ENVIRONMENTAL TRANSPORT Descriptors: AQUIFERS; FLUID FLOW; SEAWATER; TIDE Broader Terms: HYDROGEN COMPOUNDS; ISLANDS; MARSHALL ISLANDS; MASS TRANSFER +7 MICRONESIA; OCEANIA; OXYGEN COMPOUNDS; WATER Subject Categories: 580100* -- Geology & Hydrology -INIS Subject Categories: B31* -- Land 10/5/796 00768442 (Item 496 from file: 103) ERA-06-024347; BRA-06-024347; EDB-81-076703 Author(s): Spies, (-1989) Title: Dynamics of radionuclide exchange in the calcareous algae Halimeda at Enewetak Atoll Affiliation: Source: Univ. Limnol. R.B.; Marsh, Oceanogr. Publication Date: Jan 1981 Contract Number K.V.; of California, (DOE): Kercher, Livermore (United States) p 74-85 v 26:1. ERA Coden: LIOCA W-7405-ENG-48 Document Type: Journal Article; Numerical data Language: English Journal Announcement: EDB8107 Subfile: J.R. (Energy Research Abstracts); TIC (Technical Information radionuclides was measured. Data for /sup 60/Co, /sup 137/Cs, and /sup 102m/Rh were fit to loss curves by using one term for exponential loss; data for /sup 155/Eu, /sup 239+240/Pu, and /sup 241/Am required two terms. For each radionuclide, compartment size and transfer functions were determined for the appropriate one- and two-compartment models. Of 26 possible two-compartment models, only seven gave solutions with our data. Nearly identical loss rates were obtained for /sup 155/Eu, /sup 239+240/Pu}, and /sup 241/Am in the fast-exchanging compartments for all seven models. The uptake rates for these nuclides were also similar when uptake rates were normalized to local sediment concentrations. The fast-exchanging compartment probably corresponds to the mucilage surface layer of the coenocytic filaments. The identity of the 900396] Center). Country of Origin: United States Abstract: Measurements of /sup 239+240/Pu in the detrital inclusions and in acid-soluble and acid-insoluble fractions of Halimeda macrophysa showed a 10-fold higher concentration in the acid-insoluble coenocytic filaments than in the acid-soluble fraction. In a depuration experiment with Halimeda incrassata at Enewetak Atoll the loss rate of six