Assessment of groundwater vulnerability to pollution in Dire Dawa,Ethiopia using DRASTIC

Assessment of groundwater vulnerability to pollution is an effective tool for the delineation of groundwater protection zones. DRASTIC approach was used to determine vulnerability zones in Dire Dawa groundwater basin, a semiarid region of Ethiopia. Maps of the seven DRASTIC parameters were prepared. GIS-ArcView was used for mapping and performing weighted-overlay analysis. The result of the analysis indicated that eastern part of the study area, in which Dire Dawa town is located, is highly vulnerable. A low aquifer vulnerability class was determined for the western portion of the study area as a result of greater groundwater depths, higher relative soil-clay content, and relatively low recharge rates for this area. The area between the two zones is of medium vulnerability. Observed nitrate concentrations in boreholes are in accordance with the vulnerability map. Some of the boreholes in the Sabian well field (Dire Dawa area) already deliver groundwater with nitrate levels significantly exceeding health standards set by the World Health Organization, while boreholes in the western part (low vulnerability zone) contain almost no nitrate. The result of this study is useful for risk assessments and for the development of effective groundwater management strategies for this region and others like it.     

The socioeconomic impacts of nuclear generating stations: An analysis of the Rancho Seco and peach bottom facilities

This paper presents the results of a comparative analysis of the socioeconomic impacts of the construction and operation of two nuclear generating stations. Although the construction of nuclear power plants is typically a multiyear process utilizing large numbers of workers and requiring large expenditures for equipment and materials, the socioeconomic changes in the areas in which the plants are located were small and temporary. The extent and size of the changes were found to be related to the size of the work force residing in the local area, the magnitude of local utility and contractor purchases, the amount of tax payments resulting from the plant, and the level of involvement of area groups over plant-related issues.     

Trace element zoning in pyroxenes from ODP Hole 735B gabbros: diffusive exchange or synkinematic crystal fractionation?

Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions, trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation or differentiation by deformation (Natland and Dick in J Volcanol Geotherm Res 110(3–4):191–233, 2001) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges.     

Post-drilling destabilization of temperature profile in borehole Yaxcopoil-1, Mexico

As part of the International Continental Scientific Drilling Program (ICDP), the 1.5-km-deep borehole Yaxcopoil-1, located in the Chixculub meteor impact structure in Mexico, has undergone further study after drilling operations ceased. Temperature logs were repeated ten times at intervals 0.3–0.8, 15, 24 and 34 months after borehole shut-in. The logs bear a distinct signature of transient heat transfer by groundwater flow manifested by a gradual distortion of the linear temperature profile when a cold wave of 0.8–1.6°C amplitude was detected propagating downward from 145 to 312 m at a rate of 4–6 m/month. To understand the nature of this moving anomaly, a 20-day monitoring of the cold wave was carried out at a depth of 307 m that showed further cooling of 0.6°C during the first 16 days of the passage followed by temperature stabilisation. As an explanation of this unusual phenomenon, a theory is proposed, whereby the drilling mud has accumulated within the overlying and cooler highly porous and permeable karstic rocks during the drilling and migrates downward. The observed migration rate suggests a permeability higher than 10^?11 m². This indicates a high vulnerability to contamination of the only freshwater aquifer in the Yucatan region.     

Stratigraphic and geochemical study of the organic-rich black shales in the Tarcău Nappe of the Moldavidian Domain (Carpathian Chain,Romania)

An integrated stratigraphic analysis has been made of the Tarcău Nappe (Moldavidian Domain, Eastern Romanian Carpathians), coupled with a geochemical study of organic-rich beds. Two Main Sequence Boundaries (Early Oligocene and near to the Oligocene–Aquitanian boundary, respectively) divide the sedimentary record into three depositional sequences. The sedimentation occurred in the central area of a basin supplied by different and opposite sources. The high amount of siliciclastics at the beginning of the Miocene marks the activation of the “foredeep stage”. The successions studied are younger than previously thought and they more accurately date the deformation of the different Miocene phases affecting the Moldavidian Basin. The intervals with black shales identified are related to two main separate anoxic episodes with an age not older than Late Rupelian and not before Late Chattian. The most important organic-rich beds correspond to the Lower Menilites, Bituminous Marls and Lower Dysodilic Shales Members (Interval 2). These constitute a good potential source rock for petroleum, with homogeneous Type II oil-prone organic matter, highly lipidic and thermally immature. The deposition of black shales has been interpreted as occurring within a deep, periodically isolated and tectonically controlled basin.     

Differential modulation of eastern oyster (<Emphasis Type="Italic">Crassostrea virginica</Emphasis>) disease parasites by the El-Niño-Southern Oscillation and the North Atlantic Oscillation

The eastern oyster (Crassostrea virginica) is affected by two protozoan parasites, Perkinsus marinus which causes Dermo disease and Haplosporidium nelsoni which causes MSX (Multinucleated Sphere Unknown) disease. Both diseases are largely controlled by water temperature and salinity and thus are potentially sensitive to climate variations resulting from the El Niño-Southern Oscillation (ENSO), which influences climate along the Gulf of Mexico coast, and the North Atlantic Oscillation (NAO), which influences climate along the Atlantic coast of the United States. In this study, a 10-year time series of temperature and salinity and P. marinus infection intensity for a site in Louisiana on the Gulf of Mexico coast and a 52-year time series of air temperature and freshwater inflow and oyster mortality from Delaware Bay on the Atlantic coast of the United States were analyzed to determine patterns in disease and disease-induced mortality in C. virginica populations that resulted from ENSO and NAO climate variations. Wavelet analysis was used to decompose the environmental, disease infection intensity and oyster mortality time series into a time–frequency space to determine the dominant modes of variability and the time variability of the modes. For the Louisiana site, salinity and Dermo disease infection intensity are correlated at a periodicity of 4 years, which corresponds to ENSO. The influence of ENSO on Dermo disease along the Gulf of Mexico is through its effect on salinity, with high salinity, which occurs during the La Niña phase of ENSO at this location, favoring parasite proliferation. For the Delaware Bay site, the primary correlation was between temperature and oyster mortality, with a periodicity of 8 years, which corresponds to the NAO. Warmer temperatures, which occur during the positive phase of the NAO, favor the parasites causing increased oyster mortality. Thus, disease prevalence and intensity in C. virginica populations along the Gulf of Mexico coast is primarily regulated by salinity, whereas temperature regulates the disease process along the United States east coast. These results show that the response of an organism to climate variability in a region is not indicative of the response that will occur over the entire range of a particular species. This has important implications for management of marine resources, especially those that are commercially harvested.     

Mesoscale model simulation of low level equatorial winds over Borneo during the haze episode of September 1997

The large-scale vegetation fires instigated by the local farmers during the dry period of the major El Niño event in 1997 can be considered as one of the worst environmental disasters that have occurred in southeast Asia in recent history. This study investigated the local meteorology characteristics of an equatorial environment within a domain that includes the northwestern part of Borneo from the 17 to 27 September 1997 during the height of the haze episode by utilizing a limited area three-dimensional meteorological and dispersion model, The Air Pollution Model (TAPM).Daily land and sea breeze conditions near the northwestern coast of Borneo in the state of Sarawak, Malaysia were predicted with moderate success by the index of agreement of less than one between the observed and simulated values for wind speed and a slight overprediction of 2.3 of the skill indicator that evaluates the standard deviation to the observed values. The innermost domain of study comprises an area of 24,193 km², from approximately 109°E to 111°E, and from 1°N to 2.3°N, which includes a part of the South China Sea. Tracer analysis of air particles that were sourced in the state of Sarawak on the island of Borneo verified the existence of the landward and shoreward movements of the air during the simulation of the low level wind field. Polluted air particles were transported seawards during night-time, and landwards during daytime, highlighting the recirculation features of aged and newer air particles during the length of eleven days throughout the model simulation. Near calm conditions at low levels were simulated by the trajectory analysis from midnight to mid-day on the 22 of September 1997. Low-level turbulence within the planetary boundary layer in terms of the total kinetic energy was weak, congruent with the weak strength of low level winds that reduced the ability of the air to transport the pollutants.Statistical evaluation showed that parameters such as the systematic RMSE and unsystematic RMSE between the observed and simulated values indicated the modest skill of the model in simulating the low level winds. Otherwise, the equatorial meteorological parameters such as wind speed and temperature were successfully simulated by the model with comparatively high correlation coefficients, lower RMSEs and moderately high indices of agreement with observed values.     

Modeling Bedload Transport of Juvenile Bivalves: Predicted Changes in Distribution and Scale of Postlarval Dispersal

The potential consequences of bedload transport of postlarvae for patterns of distribution of marine invertebrates were explored by developing a bedload transport model for juvenile bivalves in a small estuary in New Jersey, USA. A simple numerical model of tidal current hydrodynamics was developed based on field measurements of shear stresses near the bottom. Burrowing behavior of bivalves was incorporated into the model of bedload transport by using estimates of entrainment rates of Gemma gemma and Mya arenaria in a laboratory flume, and jump lengths of the bivalves were estimated by methods previously developed for noncohesive particles. Based on the flood domination and strong gradient of shear stresses in the Navesink estuary, our model predicted that juvenile bivalves would accumulate in the center of the estuary, traveling up to several kilometers over 30 days. Field distributions of juvenile bivalves were consistent with the model predictions for other species of bivalves but not for G. gemma, for which field distributions of both <500- and >500-μm individuals were concentrated in the eastern end of the estuary. Differences between the bedload model and G. gemma distributions suggest that spatial variation in burrowing behavior or biological interactions are playing an important role in maintaining distribution patterns of this species in spite of high levels of bedload transport. This modeling approach is applicable to other juvenile benthic invertebrates that disperse as bedload and is a useful model against which to compare field observations of rates of transport and patterns of distribution and abundance.     

Sensitivity of MM5 and WRF mesoscale model predictions of surface winds in a typhoon to planetary boundary layer parameterizations

Sea surface winds and coastal winds, which have a significant influence on the ocean environment, are very difficult to predict. Although most planetary boundary layer (PBL) parameterizations have demonstrated the capability to represent many meteorological phenomena, little attention has been paid to the precise prediction of winds at the lowest PBL level. In this study, the ability to simulate sea winds of two widely used mesoscale models, fifth-generation mesoscale model (MM5) and weather research and forecasting model (WRF), were compared. In addition, PBL sensitivity experiments were performed using Medium-Range Forecasts (MRF), Eta, Blackadar, Yonsei University (YSU), and Mellor–Yamada–Janjic (MYJ) during Typhoon Ewiniar in 2006 to investigate the optimal PBL parameterizations for predicting sea winds accurately. The horizontal distributions of winds were analyzed to discover the spatial features. The time-series analysis of wind speed from five sensitivity experimental cases was compared by correlation analysis with surface observations. For the verification of sea surface winds, QuikSCAT satellite 10-m daily mean wind data were used in root-mean-square error (RMSE) and bias error (BE) analysis. The MRF PBL using MM5 produced relatively smaller wind speeds, whereas YSU and MYJ using WRF produced relatively greater wind speeds. The hourly surface observations revealed increasingly strong winds after 0300 UTC, July 10, with most of the experiments reproducing observations reliably. YSU and MYJ using WRF showed the best agreements with observations. However, MRF using MM5 demonstrated underestimated winds. The conclusions from the correlation analysis and the RMSE and BE analysis were compatible with the above-mentioned results. However, some shortcomings were identified in the improvements of wind prediction. The data assimilation of topographical data and asynoptic observations along coast lines and satellite data in sparsely observed ocean areas should make it possible to improve the accuracy of sea surface wind predictions.     

Food Web Structure and Habitat Connectivity in Fish Estuarine Nurseries—Impact of River Flow

River flow variability is known to influence estuarine production, yet knowledge on its effect upon estuarine food webs dynamics is still scarce. Stable carbon and nitrogen isotopes were used to assess the effect of river flow in the connectivity and food web interactions between the two main fish nursery areas of the Tagus estuary. The aims of the present work were to investigate the seasonal variation in food web structure and the exchange rate of individuals of marine juvenile fish among estuarine nurseries, to compare the spring of a rainy year (2001) with that of an average year (2000), and to investigate the impact of the winter floods of 2001. A low level of connectivity was observed for the fish species that use these areas as nurseries. In low river flow conditions, two isotopically distinct food webs were established in each nursery area. These food webs were very sensitive to small variations in the freshwater input. Winter floods seem to disrupt the localized food webs that are established in low river flow periods, leading to the re-establishment of a wider food web. While in rainy years this wide food web is maintained until spring, in average years the food web undergoes fragmentation into two localized and isotopically distinctive food webs. The increase in frequency of droughts due to climate change should lower the connectivity of the estuarine fish nurseries food webs, causing habitat fragmentation and consequent loss in complexity and resilience.