The response of coastal marshes to sea-level rise: Survival or submergence?     

Denise J. Reed 《地球表面变化过程与地形》1995,20(1):39-48

In order to maintain an elevation in the intertidal zone at which marsh vegetation can survive, vertical accretion of the marsh surface must take place at a rate at least equal to the rate of relative sea-level rise. Net vertical accretion of coastal marshes is a result of interactions between tidal imports, vegetation and depositional processes. All of these factors are affected, directly or indirectly, by alterations in marsh hydrology which might occur as a result of sea-level rise. The overall response of coastal marshes to relative sea-level rise depends upon the relative importance of the inorganic and organic components of the marsh soil and the impact of increased hydroperiod on net accumulation. The varied combination of factors contributing to sediment supply, and their complexity at the scale of individual marshes, means that predicting the response of suspended sediment concentration in marsh floodwater to any changes which may occur as a result of sea-level rise, at anything other than the local scale is unlikely to be accurate. The impact of sea-level rise on net below-ground production is also complex. The sensitivity of certain species to waterlogging and soil chemical changes could result in a change in species composition or the migration of vegetation zones. Consequently, predicting the net impact of sea-level rise on organic matter accumulation is fraught with difficulties and requires improved understanding of interactions between vegetation, soil and hydrologic processes.  相似文献   

Small ion concentrations in and near clouds and fogs     

Austin W. Hogan  James R. Hickman 《Pure and Applied Geophysics》1965,60(1):176-182

Summary A mobile small ion and condensation nuclei laboratory was used to study small ion concentrations in and near orographic clouds, low cloud bases, and fogs. It was found that these areas of diminished visibility exist in a conductivity well, characterized by a small ion concentration of less than 200 small ions per cm³, surrounded by an area of increasing small ion concentration, until the concentration exceeds 400 small ions per cm³ 500 to 1000 feet below the base of the cloud. It was also observed that small ion concentration increases during the dissipation of fog, and oscillates with the passage of large patches of drifting fog.  相似文献   

Formation of regolith-collapse sinkholes in southern Illinois: Interpretation and identification of associated buried cavities     

S. V. Panno  C. P. Wiebel  P. C. Heigold  P. C. Reed 《Environmental Geology》1994,23(3):214-220

Three regolith-collapse sinkholes formed near the Dongola Unit School and the Pentecostal Church in the southern Illinois village of Dongola (Union County) during the spring of 1993. The sinkholes appeared over a three-month period that coincided with development of a new municipal well. The new well was drilled through clay-rich, valley-fill sediment into karstified limestone bedrock. The piezometric surface of the limestone aquifer is above land surface, indicating the presence of an upward hydraulic gradient in the valley and that the valley fill is acting as a confining unit. Pumping during development of the well lowered the piezometric surface of the limestone aquifer to an elevation below the base of the valley fill. It is hypothesized that drainage of water from the sediments, the resulting loss of hydrostatic pressure and buoyant force in overlying sediments, increased intergranular pressure, and the initiation of groundwater flow toward the well resulted in rapid sediment transport, subsurface erosion, and collapse of the valley-fill sediment. The sinkholes follow an approximately east-west alignment, which is consistent with one of the two dominant alignments of passages of nearby joint-controlled caves. A constant electrode-separation resistivity survey of the school playground was conducted to locate areas that might contain incipient sinkholes. The survey revealed a positive resistivity anomaly trending N75E in the southern part of the study area. The anomaly is linear, between 5 and 10 m wide, and its trend either intersects or is immediately adjacent to the three sinkholes. The anomaly is interpreted to be a series of pumping-induced cavities in the valley-fill sediments that formed over a preexisting crevice in the karstified bedrock limestone.  相似文献   

Lithium tracer-diffusion in an alkali-basaltic melt — An ion-microprobe determination     

R.K. Lowry  S.J.B. Reed  J. Nolan  P. Henderson  J.V.P. Long 《Earth and Planetary Science Letters》1981,53(1):36-40

An ion-microprobe-based technique has been used to measure lithium tracer-diffusion coefficients (D_Li) in an alkali-basaltic melt at 1300, 1350 and 1400°C. The results can be expressed in the form:D_Li=7.5 ×10^?2exp(?27,600/RT)cm²S^?1The results show significantly faster diffusion rates than those previously recorded for other monovalent, divalent and trivalent cations in a tholeiitic melt. Consequently, diffusive transport of ions acting over a given time in a basaltic melt can produce a wider range of transport distance values than hitherto supposed. Hence, it is concluded that great care should be exercised when applying diffusion data to petrological problems.  相似文献   

Lithium diffusion in silicate melts     

G.J. Cunningham  P. Henderson  R.K. Lowry  J. Nolan  S.J.B. Reed  J.V.P. Long 《Earth and Planetary Science Letters》1983,65(1):203-205

  相似文献   

Gulf of Mexico,ocean-color surface-truth measurements     

R. W. Austin 《Boundary-Layer Meteorology》1980,18(3):269-285

In October 1977, a major remote sensing experiment was conducted in the Gulf of Mexico, in preparation for the launch of NIMBUS-7 which carried the Coastal Zone Color Scanner. Two major vessels obtained surface-truth measurements, while two jet aircraft at altitudes of 12.5 and 19.5 km obtained images of the surrounding ocean in 10 spectral bands. Measurements obtained in the surface water from the NOAA vessel Researcher of the spectral downwelling irradiances, upwelling radiances, attenuation and scattering properties are described.  相似文献   

Calculation of multicomponent chemical equilibria and reaction processes in systems involving minerals,gases and an aqueous phase   总被引：1，自引：0，他引：1  

Mark H Reed 《Geochimica et cosmochimica acta》1982,46(4):513-528

The compositional characteristics of many geochemical systems which involve the interaction of natural aqueous solutions with minerals and gases are conveniently described using the following thermodynamic components: Cl^?, SO₄⁼, HS^?, CO₃⁼, H⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, Fe⁺⁺, Zn⁺⁺, Cu⁺, Al⁺⁺⁺, SiO₂ and H₂O. A set of mass balance and mass action equations equal in number to the number of components plus the number of saturated minerals (and gases) is defined for a specified temperature, pressure and bulk composition. The mass balance equations include terms for minerals, gases and the molalities of aqueous complexes and dissociated species. This set of non-linear equations can be solved with the aid of a computer using'a Newton-Raphson technique. The calculation takes account of aqueous ion complexing, oxidation-reduction equilibria, activity coefficients, non-unit water activity and solid solutions. The use of H⁺, SO₄⁼, HS^? and H₂O as components allows straightforward treatment of processes involving oxidation-reduction, evaporation, boiling and changes of total aqueous H⁺ due to hydrolysis, mineral reaction or temperature change. One product of this approach is a technique for calculating pH at high temperature from measurement of pH at room temperature.By linking a series of discrete overall heterogeneous equilibrium calculations in which incremental changes of bulk composition, temperature or pressure are made, dynamic geochemical processes can be modeled. Example calculations for two such processes are given. These are the heating of seawater from 25° to 300°C and the isothermal irreversible reaction of rhyolite with an aqueous solution at 250°C.  相似文献   

Zinc and copper levels in Belfast Lough     

M.S. McGrath  J. Austin 《Marine pollution bulletin》1979,10(3):86-88

A survey of dissolved zinc, copper, oxygen and biochemical oxygen demand in Belfast Lough has been carried out. Zinc and to a lesser extent copper occur at elevated levels compared with a non-industrialized area of the Irish Sea. Zinc levels are particularly high in the marginal waters of the north shore of the lough. Dissolved oxygen and biochemical oxygen demand levels indicate that pollution of the lough by oxygendemanding wastes is not a serious problem.  相似文献   

Citation I Biogeochemistry of Mono Lake,California     

Walter E. Reed 《Geochimica et cosmochimica acta》1979,43(3):446

  相似文献   

Concentrations and thermal release of Hg from iron and zinc sulfides     

G.W. Reed Jr.  S. JovanovicA.C. Tennissen 《Earth and Planetary Science Letters》1972

Hg contents ranging from 0.026 to 0.19 and 0.1 to 344 ppm were measured by activation analysis in a number of pyrite and sphalerite samples, respectively. The release of Hg based on stepwise heating shows a correlation with metamorphic grade of the pyrite samples and with Fe content of the sphalerite samples. Experiments were undertaken to study the equilibration of Hg at different temperatures in Hg-doped laboratory prepared ZnS and FeS₂. On subsequent volatilization, trends in the Hg release were observed which paralleled those in the sulfide minerals.  相似文献