Estimation of hydraulic conductivity in an alluvial system using temperatures

Well water temperatures are often collected simultaneously with water levels; however, temperature data are generally considered only as a water quality parameter and are not utilized as an environmental tracer. In this paper, water levels and seasonal temperatures are used to estimate hydraulic conductivities in a stream-aquifer system. To demonstrate this method, temperatures and water levels are analyzed from six observation wells along an example study site, the Russian River in Sonoma County, California. The range in seasonal ground water temperatures in these wells varied from <0.2 degrees C in two wells to approximately 8 degrees C in the other four wells from June to October 2000. The temperature probes in the six wells are located at depths between 3.5 and 7.1 m relative to the river channel. Hydraulic conductivities are estimated by matching simulated ground water temperatures to the observed ground water temperatures. An anisotropy of 5 (horizontal to vertical hydraulic conductivity) generally gives the best fit to the observed temperatures. Estimated conductivities vary over an order of magnitude in the six locations analyzed. In some locations, a change in the observed temperature profile occurred during the study, most likely due to deposition of fine-grained sediment and organic matter plugging the streambed. A reasonable fit to this change in the temperature profile is obtained by decreasing the hydraulic conductivity in the simulations. This study demonstrates that seasonal ground water temperatures monitored in observation wells provide an effective means of estimating hydraulic conductivities in alluvial aquifers.     

Short-Term and Interannual Variability in Primary Production in the Low-Salinity Zone of the San Francisco Estuary

We measured primary production during spring?Csummer 2006?C2007 to determine the carbon supply to the low-salinity pelagic food web of the San Francisco Estuary (SFE). Weekly or biweekly samples were taken at three stations of fixed salinity for size-fractionated primary production and biomass, both as chlorophyll and from biovolume based on counts. Error variance in productivity estimates arose mainly from the depth integration of ¹⁴C uptake, showing the importance of productivity measurements at high light levels for estimates of depth-integrated production. Temporal and spatial variability in production were surprisingly small. Combining data from this study with long-term monitoring data, productivity and biomass were variable in time and salinity but without persistent patterns and with infrequent blooms. Production within the low-salinity zone was unresponsive to variation in freshwater flow, in contrast to findings in other estuaries where nutrient loading drives variability in production and other regions of the SFE where production responds to residence time or to stratification. Estimated annual primary production was only 25 and 31?g?C?m^?2?year^?1 during 2006 and 2007, only half of it in cells >5???m. These results imply that phytoplankton provided poor food web support for higher trophic levels, probably contributing to the long-term decline in fish abundance in the brackish to freshwater region of the estuary.     

Low-cost water-lifting from groundwater sources: a comparison of the EMAS Pump with the Rope Pump

In sub-Saharan Africa, low-cost groundwater supply systems offer great opportunities for the current unserved population of >300 million to access drinking water. A comparative study was performed in Uganda of the EMAS Pump (designed by Escuela Móvil Aguas y Saneamiento Básico) with the trade-named Rope Pump, two low-cost manual water-lifting devices appropriate to pumping from shallow groundwater sources. Pumping rates, energy expended, material costs, and construction requirements were analyzed. Focus was on low-cost application for use in shallow groundwater systems at the household level in developing countries, particularly in sub-Saharan Africa. The study site was northern Uganda, with testing performed at several drilled boreholes. Two variants of each pump were tested by a male and female user, pumping from multiple static water-level depths ranging from 5 to 28 m. Results demonstrated the most common version of the EMAS Pump to perform similarly to the comparable version of the Rope Pump in terms of average pumping rate at depth range 5 to 18 m (93–111%), but less so at deeper depths (63–85%). Normalized pumping rates (considering energy expended) accentuated differences between these versions of the EMAS Pump and Rope Pump (47–97%). Cost of materials to construct the EMAS Pump were 21–60% those of the Rope Pump, and EMAS Pump construction requirements were also less. Based on the assessed factors, it is concluded that the EMAS Pump has potential for success in “self-supply” groundwater systems in sub-Saharan Africa and is particularly appropriate to link with low-cost shallow groundwater sources.     

The spontaneous fission rate of U-238 and fission track dating

The rate of spontaneous fission decay of uranium-238 (λ_f²³⁸) was determined in 4π-geometry by the fission track method. Uranium glasses of known age of manufacture were used. Spontaneous tracks have accumulated since the time of manufacture and induced tracks to determine the uranium content were produced by thermal neutron irradiations. Spontaneous tracks in all glasses were found to be partially annealed. By correcting for this annealing effect, a (λ_f²³⁸) = 8.7 ± 0.6 × 10^?17yr^?1 was obtained. Uncertainty in the neutron dose is the largest source of error.     

Preliminary study on the preservation of giant clam (Tridacnidae) shells from the Balobok Rockshelter archaeological site,south Philippines

Tridacnidae shells, a valuable archive of past environments, are common in the Balobok Rockshelter archaeological site on Sanga‐Sanga Island in the south Philippines. This site was occupied during the mid‐Holocene (ca. 5000–8800 ¹⁴C yr B.P.), a period of Neolithic cultural expansion in the Philippines. This paper focuses on the preservation of two shell specimens, Hippopus hippopus and Tridacna maxima, unearthed from two mid‐Holocene layers within the rockshelter. The shells' mineralogy and microstructure (prismatic and crossed‐lamellar) were studied using micro‐Fourier transform infrared spectroscopy and scanning electron microscopy to determine if the samples were suitable as paleoenvironmental records. Both shells are still aragonitic but aragonite crystals of both microstructure types are partly dissolved. This dissolution, characteristic of meteoric water alteration, precludes their utility in paleoenvironmental geochemical studies. Nevertheless, these shells are abundant in archaeological sites in the region and may be better preserved in other depositional contexts; more studies on Philippine Tridacnidae shell diagenesis are needed. © 2011 Wiley Periodicals, Inc.