A geochemical survey of St. Lucia, West Indies

The Los Alamos National Laboratory conducted a reconnaissance-scale geochemical exploration program on the island of St. Lucia during September 1983. Totals of 307 stream-sediment and 55 beach-sand samples were collected and analyzed for a suite of 44 elements. Data interpretation utilized computer-generated color images. Several anomalies were delineated, the most significant of which indicate previously unrecognized Au mineralization in two areas.     

Trace elements in fines from the Apollo 15 deep drill

No systematic variations in concentrations with depth were found for 1O trace elements in samples from the Apollo 15 deep drill. Presence of a significant amount of KREEP is indicated.     

Spatial gradients in the flow over an estuarine channel

Acoustic Doppler current profiles were measured for a twelve-hour period on February 21, 1997 across Thimble Shoal channel, lower Chesapeake Bay, for the purpose of determining bathymetrically-induced spatial gradients in the flow and their implications for the lateral momentum balance in estuaries. A least-squares fit to semidiurnal and quarter-diurnal harmonics was used to separate the tidal and subtidal contributions to the observed flow. The period of observation was characterized by onshore winds and subtidal inflow everywhere along the transect sampled but strongest in the channel. Spatial gradients in both the tidal and subtidal horizontal flows showed that the greatest lateral shears and convergences were found where the bathymetric changes were sharpest, i.e., on the shoulders of the channel. The ratio of the quarter-diurnal to the semidiurnal tidal amplitudes was greatest over the channel shoulders, for both the along- and across-estuary flow components, and indicated the importance of non-linear effects there. The nonlinear term caused by across-estuary divergence was larger than the Coriolis term over the channel shoulders. The nonlinear contribution was comparable to the Coriolis acceleration in the subtidal and tidal lateral momentum balances. For the tidal balance, the local accelerations were also as important as the Coriolis accelerations. Equivalent results in the momentum balances were obtained with another data set of October 1993. Contrary to the customary assumption, the across-estuary momentum balance in this area was ageostrophic.     

Component flow processes at four streams in the Catskill Mountains,New York,analysed using episodic concentration/discharge relationships

Plots of solute concentration against discharge have been used to relate stream hydrochemical variations to processes of flow generation, using data collected at four streams in the Catskill Mountains, New York, during the Episodic Response Project of the US Environmental Protection Agency. Results suggest that a two‐component system of shallow and deep saturated subsurface flow, in which the two components respond simultaneously during hydrologic events, may be applicable to the study basins. Using a large natural sea‐salt sodium input as a tracer for precipitation, it is argued that an additional distinction can be made between pre‐event and event water travelling along the shallow subsurface flow path. Pre‐event water is thought to be displaced by infiltrating event water, which becomes dominant on the falling limb of the hydrograph. Where, as appears to be the case for sulfate, a solute equilibrates rapidly within the soil, the pre‐event–event water distinction is unimportant. However, for some solutes there are clear and consistent compositional differences between water from the two sources, evident as a hysteresis loop in concentration–discharge plots. Nitrate and acidity, in particular, appear to be elevated in event water following percolation through the organic horizon. Consequently, the most acidic, high nitrate conditions during an episode generally occur after peak discharge. A simple conceptual model of episode runoff generation is presented on the basis of these results. Copyright © 1999 John Wiley & Sons, Ltd.