Simulating the response of a closed‐basin lake to recent climate changes in tropical West Africa (Lake Bosumtwi,Ghana)     

Timothy M. Shanahan  Jonathan T. Overpeck  W. E. Sharp  Christopher A. Scholz  Justice A. Arko 《水文研究》2007,21(13):1678-1691

Historical changes in the level of Lake Bosumtwi, Ghana, have been simulated using a catchment‐scale hydrological model in order to assess the importance of changes in climate and land use on lake water balance on a monthly basis for the period 1939–2004. Several commonly used models for computing evaporation in data‐sparse regions are compared, including the Penman, the energy budget, and the Priestley–Taylor methods. Based on a comparison with recorded lake level variations, the model with the energy‐budget evaporation model subcomponent is most effective at reproducing observed lake level variations using regional climate records. A sensitivity analysis using this model indicates that Lake Bosumtwi is highly sensitive to changes in precipitation, cloudiness and temperature. However, the model is also sensitive to changes in runoff related to vegetation, and this factor needs to be considered in simulating lake level variations. Both interannual and longer‐term changes in lake level over the last 65 years appear to have been caused primarily by changes in precipitation, though the model also suggests that the drop in lake level over the last few decades has been moderated by changes in cloudiness and temperature over that time. Based on its effectiveness at simulating the magnitude and rate of lake level response to changing climate over the historical record, this model offers a potential future opportunity to examine the palaeoclimatic factors causing past lake level fluctuations preserved in the geological record at Lake Bosumtwi. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Microbial remains in some earliest Earth rocks: Comparison with a potential modern analogue   总被引：1，自引：1，他引：0  

Miryam Glikson  Lawrence J. Duck  Suzanne D. Golding  Axel Hofmann  Robert Bolhar  Robyn Webb  Justice C.F. Baiano  Lindsay I. Sly 《Precambrian Research》2008,164(3-4):187-200

Carbonaceous matter (CM) from ca. 3.5 Ga hydrothermal black cherts of the Pilbara Craton of Western Australia and the Barberton Greenstone Belt of South Africa yielded transmission electron microscopy (TEM) images that are suggestive of microbial remains and possible remnants of microbial cell walls. These are compared to a potential modern analogue, the hyperthermophilic Methanocaldococcus jannaschii, derived from an active seafloor hydrothermal environment and cultured under similar conditions. A striking resemblance to the early Archaean forms was evident in wall structure and thermal degradation mode. Cell disintegration of the cultures occurred at 100 °C marking the limits of life. Complete disintegration, deformation and shrinkage occurred at 132 °C. A multidisciplinary approach to the characterisation of the CM was undertaken using organic petrology, TEM coupled with electron dispersive spectral analysis (EDS), high resolution TEM (HRTEM) to determine molecular ordering, and elemental and carbon isotope geochemistry. Reflectance measurements of the CM to determine thermal stress yielded a range of values corresponding to several populations, and pointing to different sources and processes. The δ¹³C values of Dresser Formation CM (−36.5 to −32.1‰) are negatively correlated with TOC (0.13–0.75%) and positively correlated with C/N ratio (134–569), which is interpreted to reflect the relative abundance of high R_o/oxidised/recycled CM and preferential loss of ¹²C and N during thermal maturation. TEM observations, inferred carbon isotopic heterogeneity and isotope fractionations of −27 to −32‰ are consistent with the activity of chemosynthetic microbes in a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the CM.  相似文献   

The influences of land use and sanitation infrastructure on flooding in Kumasi,Ghana     

Justice Kufour Owusu-Ansah 《GeoJournal》2016,81(4):555-570

Each year during the rainy seasons, the Ghanaian media is dominated by banner headlines of flooded urban landscapes along with emergency response teams doling out relief items to the victims. However, when the rains subside and the floods are no longer newsworthy, the key stakeholders return to their normal duties only to await the next cycle of rains with bated breath. Based on the analyses of secondary and fieldwork data, the paper found no significant change in recent rainfall patterns that could account for the city’s flood problems. Rather, the impervious surfaces created through the removal of wetlands, riparian lands and urban vegetation, along with deposits of sediments and domestic wastes into streams and drains, have combined to slow down the velocity of stormwater flows and allowing it to disperse into the surrounding built up areas in lower terrains. The paper recommends the construction of modern city-wide sewerage systems to cope up with the current and predicted rainfall patterns, complemented by non-structural approaches including the protection of wetlands and urban vegetation to reduce the amount of storm water flows. Planners should anticipate and project future land use demands to cater emerging activities such as LPG stations which currently take sites in open space or flood ways and manage and direct physical development into low risk locations. Other measures would include the consideration of free domestic waste collection systems, mandatory flood insurance schemes on properties, with premiums assessed based on site risks, the development of early warning systems to minimize the effects of floods.  相似文献   

Spatial and temporal intercomparison of four global burned area products     

Michael L. Humber  Luigi Boschetti  Louis Giglio  Christopher O. Justice 《International Journal of Digital Earth》2019,12(4):460-484

We characterize the agreement and disagreement of four publically available burned products (Fire CCI, Copernicus Burnt Area, MODIS MCD45A1, and MODIS MCD64A1) at a finer spatial and temporal scale than previous assessments using a grid of three-dimensional cells defined both in space and in time. Our analysis, conducted using seven years of data (2005–2011), shows that estimates of burned area vary greatly between products in terms of total area burned, the location of burning, and the timing of the burning. We use regional and monthly units for analysis to provide insight into the variation between products that can be lost when considering products yearly and/or globally. Comparison with independent, contemporaneous MODIS active fire observations provides one indication of which products most reasonably capture the burning regime. Our results have implications for the use of global burned area products in fire ecology, management and emissions applications.  相似文献   

Classification of boreal macrotidal littoral zone habitats in the Gulf of Maine: comparison of IKONOS and CASI multispectral imagery     

Peter Foster Larsen  David A. Phinney  Fay Rubin  David Justice 《国际地球制图》2013,28(6):457-472

Increasingly, remote sensing has become a useful tool for mapping and measuring terrestrial and aquatic environments. Advances in the spatial and spectral resolution of satellite-borne sensors have allowed affordable investigations of littoral macrotidal coastal systems that previously required more costly aircraft-based imagery. In this communication, we compare the results from analysis of a 4 m spatial resolution, multispectral IKONOS satellite image of the intertidal habitats of Islesboro, Maine, USA with that of an aerial compact airborne spectral imager survey of the same regions captured 4 years earlier. There was 72% agreement between the surveys in spite of the temporal gaps between the images. Accuracy varied by habitat class and the perceived error can be assigned to temporal and definitional issues rather than basic acquisition and analytic protocols. Most of the error can be explained by: (1) inadequacy of training sites, (2) temporal variations and (3) class definitions. We conclude that IKONOS imagery provides sufficient spatial and spectral resolution to map and monitor diverse intertidal habitats as found in the macrotidal Gulf of Maine.  相似文献   

Hydrochemical and isotopic characteristics of groundwater in the Ndop plain,northwest Cameroon: resilience to seasonal climatic changes     

Mengnjo Jude Wirmvem  Takeshi Ohba  Justice Yuven Suila  Wilson Yetoh Fantong  Nchemty Oscar Bate  Seigo Ooki  Engome Regina Wotany  Asobo Nkengmatia Elvis Asaah  Samuel Ndonwi Ayonghe  Gregory Tanyileke  Joseph Victor Hell 《Environmental Earth Sciences》2014,72(9):3585-3598

Shallow groundwater (>30 mbgl) is an essential source of drinking water to rural communities in the Ndop plain, northwest Cameroon. As a contribution to water management, the effect of seasonal variation on the groundwater chemistry, hydrochemical controls, drinking quality and recharge were investigated during the peaks of the dry (January) and rainy (September) seasons. Field measurements of physical parameters were preceded by sampling 58 groundwater samples during both seasons for major ions and stable isotope analyses. The groundwater, which was barely acidic (mean pH of 6) and less mineralised (TDS < 272 mg/l), showed no significant seasonal variation in temperature, pH and TDS during the two seasons. The order of cation abundance (meq/l) was Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ in the dry and rainy seasons, respectively, but that of anions ( \( {\text{HCO}}_{3}^{ - } \)  >  \( {\text{NO}}_{3}^{ - } \)  > Cl^? >  \( {\text{SO}}_{4}^{2 - } \)  > F^?) was similar in both seasons. This suggests a negligible effect of seasonal variations on groundwater chemistry. The groundwater, which was CaMgHCO₃ and NaHCO₃, is chemically evolved rainfall (CaMgSO₄Cl) in the area. Silicate mineral dissolution and cation-exchange were the main controls on groundwater chemistry while there was little anthropogenic influence. The major ions and TDS concentrations classified the water as suitable for human consumption as per WHO guidelines. The narrow cluster of δ¹⁸O and δD of same groundwater from both seasons between the δ¹⁸O and δD values of May–June precipitation along the Ndop Meteoric Water Line indicates meteoric origin, rapid recharge (after precipitation) and timing of recharge between May and June rainfall. Diffuse groundwater recharge mainly occurs at low altitudes (<1,400 m asl) within the plain. Besides major ions and TDS, the similar δ¹⁸O and δD of groundwater from both seasons indicate a consistent groundwater recharge and flow pattern throughout the year and resilience to present day short-term seasonal climatic variations. However, controlled groundwater abstraction is recommended given the increasing demand.  相似文献