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1.
This study integrated surface and subsurface stratigraphic data with geophysical logs and hydrogeologic data in order to
characterize the hydraulic properties of the Silurian dolomite in northeastern Wisconsin. Silurian stratigraphy consists of
predictable alternations of characteristic facies associations. A vertical profile of hydraulic conductivity, obtained from
short-interval packer tests in a core hole that penetrates a majority of the Silurian section, indicates that hydraulic conductivity
ranges over five orders of magnitude (10–1 to 10–6 cm/s). Matrix conductivity is generally low and varies with texture; the finer-grained restricted-marine and transitional
facies being less permeable than the coarser-grained open-marine facies. High-conductivity values are generally associated
with bedding-plane fractures, and fracture frequency is greater in the restricted-marine facies.
High-flow features in 16 wells were identified using fluid-temperature/resistivity and heat-pulse flowmeter logs. Natural-gamma
logs were used to identify the stratigraphic position of flow features in each well and to correlate flow features to specific
stratigraphic horizons. By combining stratigraphic, geophysical, and hydrogeologic data, 14 high-permeability zones within
the Silurian aquifer have been identified and correlated in wells more than 16 km apart. These zones parallel bedding, appear
most pronounced at contacts between contrasting lithologies, and are most abundant in restricted-marine lithologies.
Electronic Publication 相似文献
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Field-based experiments were designed to investigate the release of naturally occurring, low to moderate (< 50 microg/L) arsenic concentrations to well water in a confined sandstone aquifer in northeastern Wisconsin. Geologic, geochemical, and hydrogeologic data collected from a 115 m2 site demonstrate that arsenic concentrations in ground water are heterogeneous at the scale of the field site, and that the distribution of arsenic in ground water correlates to solid-phase arsenic in aquifer materials. Arsenic concentrations in a test well varied from 1.8 to 22 microg/L during experiments conducted under no, low, and high pumping rates. The quality of ground water consumed from wells under typical domestic water use patterns differs from that of ground water in the aquifer because of reactions that occur within the well. Redox conditions in the well can change rapidly in response to ground water withdrawals. The well borehole is an environment conducive to microbiological growth, and biogeochemical reactions also affect borehole chemistry. While oxidation of sulfide minerals appears to release arsenic to ground water in zones within the aquifer, reduction of arsenic-bearing iron (hydr)oxides is a likely mechanism of arsenic release to water having a long residence time in the well borehole. 相似文献
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依据南海低纬地区SA09-040孔高分辨率的孢粉记录,自下至上划分了4个孢粉组合带。从孢粉成分的变化,重建了22.25ka B P以来的植被与气候变化历史。结果表明:孢粉主要来源于婆罗洲和周围岛屿,孢粉1带(22.25～16.6ka B P),低山雨林植被发育,为暖热气候,从测年时间看,当时为末次冰期晚期。孢粉2带(16.6～10.82ka B P,为末次冰消期),植被以热带低山雨林和低地雨林为主,针叶的松数量较多,当时的气温比现在低。孢粉3带(全新世早期,10.82～6.43ka B P),植被以热带低山雨林和低地雨林为主,针叶松属数量减少,气温比前期升高,海平面也上升。孢粉4带(全新世中晚期,6.43ka B P至今),全新世中期为炎热、湿润的气候环境,全新世晚期可能与婆罗洲现今的植被景观相近,为热、湿的气候环境。 相似文献
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Aspects of the Fine-Scale Climatology Over Lake Tanganyika as Resolved by a Mesoscale Model 总被引：1，自引：0，他引：1
Summary An hourly averaged climatology at 0.05 ° horizontal resolution over the Lake Tanganyika region was created by making simulations
with a mesoscale model (HIRLAM) using a high resolution physiography to represent the surface. Initial and boundary values
were interpolated from ECMWF analyses. Climatologies for a typical dry season month (July 1994) and wet season month (March
1994) were created by 7-day segmenting. Model results were validated by utilizing a special coastal observation network. A
number of experiments were made with changes to the physiography (mountains/no mountains, lake/no lake).
The results reveal local channelling and blocking effects of the near-surface southeasterly trade winds by the high mountain
chains in the region of the East African rift. Furthermore, surface winds display regular diurnal cycles in many places, due
to slope winds over hills and lake-land-type breezes near the coast. The diurnal coastal winds (defined by the observation
network) are reasonably well simulated. Precipitation patterns display the semi-annual march of the ITCZ across the area,
plus considerable topographic effects. There is high evaporation from lakes and wetlands during the windy dry season, while
evaporation from the moist land surface dominates the rainy season.
Received October 15, 1998/Revised September 2, 1999 相似文献
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Fish assemblages that included known predators of benthic crustaceans were compared between kelp and barren habitats in northeastern New Zealand using baited underwater video census methods. The benthic-feeding fish were observed in winter, spring/summer and autumn, as well as during night-time in spring/summer. Overall, the fish assemblages varied between barren and kelp habitat, being most marked in winter. Individual benthic-feeding species, such as grey mao mao (Scorpis lineolatus) and leatherjacket (Meuschenia scaber) were associated with barren habitat, while the spotted wrasse (Notolabrus celidotus) was more strongly associated with kelp habitat. The results suggest that changes in habitats on coastal reefs affect populations of species that are benthic predators, which may in turn influence the distribution and abundance of their prey species, such as juvenile spiny lobsters. 相似文献
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ML Camara B Mérigot F Leprieur JA Tomasini I Diallo M Diallo 《African Journal of Marine Science》2016,38(2):189-206
In a context of growing fishing pressures and recommendations for an ecosystem approach to fisheries, there is a need to monitor changes in fish communities over time. In this study, we analysed data from scientific trawl surveys carried out on the continental shelf off Guinea between 1985 and 2012. We performed factorial analyses and calculated biodiversity indices to characterise the changes in the structure and composition of fish communities that occurred over the 28-year period in this area, particularly given intensive fishing activities. We show that, over the study period, fish communities on the Guinean shelf were structured primarily according to spatial factors, with temporal changes being less pronounced than expected. However, a temporal analysis of biodiversity indices and species dominance showed that the intensification of fishing had significant effects on the general ecological features of the fish assemblages under study. There was a decrease in fish density and in mean trophic level. In addition, there were changes in species dominance, whereby large, slow-growing species with high commercial value were gradually replaced by smaller, fast-growing species of lesser commercial interest. These results from field observations are in line with some conclusions from previous modelling studies in the same geographical area, and provide further support for the hypothesis of a progressive ‘ecosystem effect of fishing’ occurring in Guinean waters. 相似文献
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Zooplankton biomass and distribution in the KwaZulu-Natal Bight were investigated in relation to environmental parameters during summer (January–February 2010) and winter (July–August 2010). Mean zooplankton biomass was significantly higher in winter (17.1 mg dry weight [DW] m–3) than in summer (9.5 mg DW m?3). In summer, total biomass was evenly distributed within the central bight, low off the Thukela River mouth and peaked near Durban. In winter, highest biomass was found offshore between Richards Bay and Cape St Lucia. Zooplankton biomass in each size class was significantly, negatively related to sea surface temperature and integrated nitrate, but positively related to surface chlorophyll a and dissolved oxygen. Zooplankton biomass was significantly related to bottom depth, with greatest total biomass located inshore (<50 m). Distribution across the shelf varied with zooplankton size. Seasonal differences in copepod size composition suggest that a smaller, younger community occupied the cool, chlorophyll-rich waters offshore from the St Lucia upwelling cell in winter, and a larger, older community occurred within the relatively warm and chlorophyll-poor central bight in summer. Nutrient enrichment from quasi-permanent upwelling off Durban and Richards Bay appears to have a greater influence on zooplankton biomass and distribution in the bight than the strongly seasonal nutrient input from the Thukela River. 相似文献
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DJ Karoly JA Cohen GA Meehl JFB Mitchell AH Oort RJ Stouffer RT Wetherald 《Climate Dynamics》1994,10(1-2):97-105
As an example of the technique of fingerprint detection of greenhouse climate change, a multivariate signal or fingerprint of the enhanced greenhouse effect is defined using the zonal mean atmospheric temperature change as a function of height and latitude between equilibrium climate model simulations with control and doubled CO2 concentrations. This signal is compared with observed atmospheric temperature variations over the period 1963 to 1988 from radiosonde-based global analyses. There is a significant increase of this greenhouse signal in the observational data over this period.These results must be treated with caution. Upper air data are available for a short period only, possibly too short to be able to resolve any real greenhouse climate change. The greenhouse fingerprint used in this study may not be unique to the enhanced greenhouse effect and may be due to other forcing mechanisms. However, it is shown that the patterns of atmospheric temperature change associated with uniform global increases of sea surface temperature, with El NinoSouthern Oscillation events and with decreases of stratospheric ozone concentrations individually are different from the greenhouse fingerprint used here. 相似文献