Saltwater intrusion and nitrate pollution in the coastal aquifer of Dar es Salaam, Tanzania

Dar es Salaam Quaternary coastal aquifer is a major source of water supply in Dar es Salaam City used for domestic, agricultural, and industrial uses. However, groundwater overdraft and contamination are the major problems affecting the aquifer system. This study aims to define the principal hydrogeochemical processes controlling groundwater quality in the coastal strip of Dar es Salaam and to investigate whether the threats of seawater intrusion and pollution are influencing groundwater quality. Major cations and anions analysed in 134 groundwater samples reveal that groundwater is mainly affected by four factors: dissolution of calcite and dolomite, weathering of silicate minerals, seawater intrusion due to aquifer overexploitation, and nitrate pollution mainly caused by the use of pit latrines and septic tanks. High enrichment of Na⁺ and Cl^? near the coast gives an indication of seawater intrusion into the aquifer as also supported from the Na–Cl signature on the Piper diagram. The boreholes close to the coast have much higher Na/Cl molar ratios than the boreholes located further inland. The dissolution of calcite and dolomite in recharge areas results in Ca–HCO₃ and Ca–Mg–HCO₃ groundwater types. Further along flow paths, Ca²⁺ and Na⁺ ion exchange causes groundwater evolution to Na–HCO₃ type. From the PHREEQC simulation model, it appears that groundwater is undersaturated to slightly oversaturated with respect to the calcite and dolomite minerals. The results of this study provide important information required for the protection of the aquifer system.     

Steps Toward a Large-Scale Solar Image Data Analysis to Differentiate Solar Phenomena

We detail the investigation of the first application of several dissimilarity measures for large-scale solar image data analysis. Using a solar-domain-specific benchmark dataset that contains multiple types of phenomena, we analyzed combinations of image parameters with different dissimilarity measures to determine the combinations that will allow us to differentiate between the multiple solar phenomena from both intra-class and inter-class perspectives, where by class we refer to the same types of solar phenomena. We also investigate the problem of reducing data dimensionality by applying multi-dimensional scaling to the dissimilarity matrices that we produced using the previously mentioned combinations. As an early investigation into dimensionality reduction, we investigate by applying multidimensional scaling (MDS) how many MDS components are needed to maintain a good representation of our data (in a new artificial data space) and how many can be discarded to enhance our querying performance. Finally, we present a comparative analysis of several classifiers to determine the quality of the dimensionality reduction achieved with this combination of image parameters, similarity measures, and MDS.     

Computer Vision for the Solar Dynamics Observatory (SDO)

In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A?completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre-Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO).     

Material ejection

This paper reviews the major discussions and conclusions of the Flares 22 Workshop concerning the physical processes involved in mass ejecta events, with an emphasis on large-scale phenomena, especially Coronal Mass Ejections (CMEs). New insights have been gained from recent data obtained from the SMM andYohkoh spacecraft and from several new ground-based radio and optical instruments, as well as from theoretical advances concerning the origins, driving mechanisms and long-term evolution of CMEs.Report of Team 5, Flares 22 Workshop, Ottawa, May 25–28, 1993.     

Empirical Modeling of Radiative <Emphasis Type="Italic">versus</Emphasis> Magnetic Flux for the Sun-as-a-Star

We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles. We use two different statistical methods to determine the underlying nature of these flux – flux relationships. First, we use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second, we use signal theory to examine the flux – flux relationships for a temporal component. We find that a well-defined temporal component exists and accounts for some of the variance in the data. This temporal component arises because active regions with high magnetic-field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux density. In most cases, the model reconstructions can account for 85 – 90% of the variability of the radiative flux from the chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures of solar and stellar variability.     

Creating a GIS-based model of marine debris "hot spots" to improve efficiency of a lobster trap debris removal program

Debris removal programs are combatting the accumulation of derelict fishing gear and other debris in marine habitats. We analyzed 5 years of lobster trap debris removal data in Biscayne National Park, Florida to assess removal efficiency and develop spatially-explicit mapping tools to guide future removals. We generated and validated debris "hot spots" maps that combined remotely-sensed data (i.e. benthic habitat type and bathymetry) with 862 locations of previous debris collection. Our hot spot models spatially depict regions of likely debris accumulation, reducing the search area by 95% (from 332 km(2) to 18 km(2)) and encompassing 100% of the validation sites. Our analyses indicate removal contractors using sub-surface towed divers enhanced debris recovery. Additionally, the quantity of debris removed did not decrease with increased efforts, suggesting that debris supply in situ exceeds removal efforts. We conclude with the importance of coupling analysis of ongoing debris removal programs with GIS technology to improve removal efforts.     

Eclogite varieties and petrotectonic evolution of the northern Guatemala Suture Complex

ABSTRACT

Field and petrologic characteristics of two new eclogite localities within the Guatemala Suture Complex (GSC) north of the Motagua Fault are presented. The Tuncaj Hill locality exposes a coherent body of retrogressed eclogite hundreds of metres long that is associated with serpentinite of the North Motagua Unit. The Tanilar River locality exposes numerous bands and lenses of eclogite hosted in sialic gneisses of the Chuacús Complex. The Tuncaj eclogite has a two-stage prograde evolution containing the peak assemblage Grt + Omp + Ttn + Czo + Zo ± Am, formed at temperatures <720°C. In contrast, eclogites of the Tanilar unit are characterized by the paragenesis Omp + Grt + Rt ± Phg ± Qtz ± Ep giving higher peak conditions of T = 720–830°C and P = 2.1–2.7 GPa, near the stability field of coesite. Previously obtained data and our thermobaric calculations suggest distinct petrotectonic evolutions for the various types of eclogites within the suture. The lawsonite eclogites south of the Motagua Fault were probably produced in a mature Farallon subduction zone during the Early Cretaceous. The northern high-pressure (HP) blocks in serpentinite mélange and coherent amphibolite bodies with eclogite relics were generated by the Early Cretaceous subduction of the proto-Caribbean lithosphere under the Great Caribbean Arc. A continental block, the North American passive margin, reached the arc’s trench in the Campanian and was subducted to ca. 80 km depth, producing the eclogites of the Chuacús Complex. As the slab was delaminated and partially exhumed, the continental Chuacús became tectonically juxtaposed with HP blocks of the proto-Caribbean that had been accreted to the Caribbean plate forming the North Motagua Unit. The juxtaposed group migrated to mid-crustal level and was contemporaneously retrogressed under epidote-amphibolite facies conditions.     

The impact of taphonomic processes on interpreting paleoecologic changes in large lake ecosystems: ostracodes in Lakes Tanganyika and Malawi

Nonmarine ostracodes are often used as proxy indicators for the biotic response to climate as well as anthropogenic changes in large lakes. Their large numbers, small size and sensitivities to environmental conditions make them ideal for assessing how organisms respond to environmental perturbations. However, little is known about the various taphonomic processes related to preserving these organisms in the lacustrine fossil record. Without understanding the amount of time averaging associated with these assemblages, any interpretation of their biodiversity and paleoecology may be problematic.To address these issues, we conducted actualistic experiments to determine transport, time-averaging, and the amount of taphonomic bias in ostracode sub-fossil assemblages. Sand transport experiments revealed significant mixing at all sites at shallower depths and significant mixing on rocky substrates but not sandy ones. Comparisons with ostracode material collected along the experimental transects support this model and demonstrate time averaging in both the sandy and rocky substrates. Preservational models were derived from the experimental data and applied to interpreting the paleobiologic record of ostracodes from piston cores in both Lake Tanganyika and Malawi. The core record reveals assemblages that have undergone significant time-averaging, and in the case of Lake Malawi, preservational degradation. In the core examined from Tanganyika, most assemblages resemble the time-averaged experimental model with respect to species richness, percentage of articulated shells and heavy bias towards adult dead individuals. In the Malawi cores, most of the valves were preserved only as internal molds. The taphonomic signature of these samples resemble the time-averaged assemblages of Tanganyika cores, even though carapaces are not often present.Both the experimental and live/dead valve data suggest significant time-averaging and transport, smearing seasonal-yearly data in some environments involved in using ostracodes to assess biotic changes as a result of climate and or anthropogenically-induced environmental change. Ostracode species richness estimates were impacted by time averaging because transport of dead valve material occurs at high percentages in the shallow depths and on the rocky substrates, suggesting that the ostracode death assemblages in these areas will not reflect living populations. In addition, ecologic models based only upon death assemblages will be less resolved than those based upon live assemblages. A time averaging index was derived using the % dead juveniles ratio, as well as sedimentation rate and information on the population dynamics, if known.     

Effects of multi-annual climate variability on the hydrodynamic evolution (1833 to present) in a shallow aquifer system in northern Belgium

Abstract

Using a groundwater flow model and long historical meteorological time series data, the evolution of the groundwater flow regime in a multi-layered groundwater flow basin in northern Belgium during the last one and a half centuries (since 1833) is reconstructed. Model output parameters such as piezometric levels, depth to water table, seepage fluxes in the valleys and calculated baseflow to the river system are presented and inter-annual and decadal variations are evaluated against seasonal fluctuations. The main time-varying boundary condition in the model is the aquifer recharge which was estimated using the method of Thornthwaite and Mather based on precipitation and temperature data. The model does not take into account changes in boundary conditions due to changes in land use (deforestation, drainage of cultivated land) or groundwater exploitation. Variations in model output parameters are therefore only due to climatological forcing. Only the natural non-exploited state of the aquifer is considered. Although few historical piezometric measurements are available to verify model output, the results give an indication of the natural hydrodynamic variations on a time scale of decades.

Citation Van Camp, M., Coetsiers, M., Martens, K. & Walraevens, K. (2010) Effects of multi-annual climate variability on the hydrodynamic evolution (1833 to present) in a shallow aquifer system in northern Belgium. Hydrol. Sci. J. 55(5), 763–779.     

Neoendemic ground beetles and private tree haplotypes: two independent proxies attest a moderate last glacial maximum summer temperature depression of 3–4 °C for the southern Tibetan Plateau

Previous findings regarding the Last Glacial Maximum LGM summer temperature depression (maxΔT in July) on the Tibetan Plateau varied over a large range (between 0 and 9 °C). Geologic proxies usually provided higher values than palynological data. Because of this wide temperature range, it was hitherto impossible to reconstruct the glacial environment of the Tibetan Plateau. Here, we present for the first time data indicating that local neoendemics of modern species groups are promising proxies for assessing the LGM temperature depression in Tibet. We used biogeographical and phylogenetic data from small, wingless edaphous ground beetles of the genus Trechus, and from private juniper tree haplotypes. The derived values of the maxΔT in July ranged between 3 and 4 °C. Our data support previous findings that were based on palynological data. At the same time, our data are spatially more specific as they are not bound to specific archives. Our study shows that the use of modern endemics enables a detailed mapping of local LGM conditions in High Asia. A prerequisite for this is an extensive biogeographical and phylogenetic exploration of the area and the inclusion of additional endemic taxa and evolutionary lines.