Organic matter fluxes and marsh stability in a rapidly submerging estuarine marsh     

J. A. Nyman  R. D. DeLaune  S. R. Pezeshki  W. H. Patrick 《Estuaries and Coasts》1995,18(1):207-218

We studied organic matter cycling in two Gulf Coast tidal, nonsaline marsh sites where subsidence causes marine intrusion and rapid submergence, which mimics increased sea-level rise. The sites experienced equally rapid submergence but different degrees of marine intrusion. Vegetation was hummocked and much of the marsh lacked rooted vegetation. Aboveground standing crop and production, as measured by sequential harvesting, were low relative to other Gulf CoastSpartina patens marshes. Soil bulk density was lower than reported for healthyS. alterniflora growth but that may be unimportant at the current, moderate sulfate levels. Belowground production, as measured by sequential harvesting, was extremely fast within hummocks, but much of the marsh received little or no belowground inputs. Aboveground production was slower at the more saline site (681 g m^?2 yr^?1) than at the less saline site (1,252 g m^?2 yr^?1). Belowground production over the entire marsh surface averaged 1,401 g m^?2 yr^?1 at the less saline site and 585 g m^?2 yr^?1 at the more saline site. Respiration, as measured by CO₂ emissions in the field and corrected for CH₄ emissions, was slower at the less saline site (956 g m^?2 yr^?1) than at the more saline site (1,438 g m^?2 yr^?1), reflecting greater contributions byS. alterniflora at the more saline site which is known to decompose more rapidly thanS. patens. Burial of organic matter was faster at the less saline site (796 g m^?2 yr^?1) than at the more saline site (434 g m^?2, yr^?1), likely in response to faster production and slower decomposition at the less saline site. Thus vertical accretion was faster at the less saline site (1.3 cm yr^?1) than at the more saline site (0.85 cm yr^?1); slower vertical accretion increased flooding at the more saline site. More organic matter was available for export at the less saline site (1,377 g m^?2 yr^?1) than at the more saline site (98 g m^?2 yr^?1). These data indicated that organic matter production decreased and burial increased in response to greenhouse-like conditions brought on by subsidence. *** DIRECT SUPPORT *** A01BY069 00016  相似文献   

Shape preferred orientation of object populations: automatic analysis of digitized images   总被引：1，自引：0，他引：1  

Patrick Launeau  Jean-Luc Bouchez  Keith Benn 《Tectonophysics》1990,180(2-4):201-211

An automatic technique is presented for systematic shape preferred orientation (SPO) analysis of crystal fabrics in rocks. This technique is based on digitization of an image with a CCD camera and separation of an object population from its matrix. The image is analysed globally using a rotating grid that is superimposed on the square pixel grid of the computer screen. The parametric method is based on counting intercepts in all directions. The interceps rose provides information on both the orientation and strength of the SPO. Problems of hardware-related counting noise anisotropy are avoided using an original method of filtering the intercept function with a linear, sliding mask on the counting grid. The technique was tested both on single objects of different shapes and on different populations of identical objects. A very high degree of accuracy was obtained for orientation measurements. Fabric shape parameters are introduced which are specific to this intercept technique; they compare favourably with shape parameters used in axial fabric analysis.  相似文献   

Telecommunications and the Large City-Small City Divide: Evidence from Indiana Cities*     

Patrick Alles  Adrian Esparza  Susan Lucas 《The Professional geographer》1994,46(3):307-316

Urban systems are increasingly dominated by large cities that house a disproportionate share of telecommunications infrastructure. This paper investigates whether telecommunications is defining a technological divide between large and smaller cities. The paper provides a conceptual basis for large-city dominance and presents the results of surveys that investigate the use of telecommunications in medium and small Indiana cities. The survey data indicate that telecommunications is used by the set of Indiana cities, but is less prevalent among the set of smallest cities. Chi-square tests, however, suggest that city size does not adequately explain these variations in use.  相似文献   

Economic and climatic factors in ‘acreage abandonment’ over marginal cropland     

Patrick J. Michaels 《Climatic change》1985,7(2):185-202

Crop yield projections made at planting time or during the growing season often ignore the fact that an unknown percentage of planted acreage is not harvested. As a solution, we present a model for 'acreage abandonment, based upon both economic and weather variables. Weather is shown to be a much more important determinant of the decision not to harvest than is the expected price. The explained variance in abandonment of spring wheat acreage by future delivery price is approximately 16%, but rises to over 60% when weather variables are added. In a similarly designed model for winter wheat in the southern plains, the price contribution is less than 5%.The spring wheat model was tested on two extensive sets of withheld data: three-year successive deletions through the entire (1932–1975) data set, and a ten year block at the beginning of the modelling period that included substantial weather and price perturbations induced by the dust bowl, depression, and attendant market gyrations. Predictive capability was retained in both tests.Current weather appears to weigh more heavily in the abandonment decision than does future price.  相似文献   

Comparison between natural and artificial maturation series of humic coals from the Mahakam delta,Indonesia     

Marc Monthioux  Patrick Landais  Jean-Claude Monin 《Organic Geochemistry》1985,8(4):275-292

Type III (humic) organic matter from the Mahakam delta (Indonesia) was chosen to compare artificial and natural coal series. Powdered and concentrated immature organic matter was heated in sealed gold tubes for 24 hr at temperatures ranging from 250 to 550°C and under pressures ranging from 0.5 to 4 kb, with and without water. Both elemental and Rock-Eval analyses were used to characterize the products. A comparison between our results, published data and the natural model shows that, quantitatively, natural maturation is simulated better when pyrolysis is performed under confined conditions (no free volume, no diluting inert gas). Thus, pyrolysis in a medium swept by an inert gas, vacuum pyrolysis and some pyrolysis in sealed glass tubes must be considered to be poor simulation tools. The presence of water does not seem to have an essential effect. Allowing the hydrocarbons formed to reach a certain value of partial pressure seems to be important. Results are unchanged when external pressure varies from 0.5 to 4 kb.  相似文献   

Finite strains from non-coaxial strain paths. I. Computational techniques     

Patrick J. Shore  Ian J. Duncan 《Tectonophysics》1984,110(1-2)

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Importance of the oxidation/maturation pair in the evolution of humic coals     

Landais Patrick  Marc Monthioux  Jean-Dominique Meunier 《Organic Geochemistry》1984,7(3-4)

The natural thermal evolution of type III coals (Humic origin) is expressed during diagenesis by a loss of oxygen as CO₂ and H₂O. Other phenomena such as oxidation can cause extensive geochemical modifications and may complicate the effects of simple maturation.Humic coals from the Jurassic in southeastern Utah were studied by elemental analysis, Rock-Eval pyrolysis and infrared spectroscopy. In a van Krevelen diagram (atomic H/C vs atomic O/C), the samples fall within the envelope defined by 860 reference humic coals covering the entire range of diagenesis. Nevertheless, various criteria (geochemical, petrographic, geological and microscopic) cast doubt upon the interpretation that such a distribution of coal composition results from thermal maturation.The same criteria indicate the intervention of redox phenomena. Comparison of our results with those from artificial and natural oxidation shows that these coals were subjected to an oxidation process different from ordinary late alteration. This process was probably due to circulation of highly oxidizing saline water causing oxygen fixation and the transformation of carboxyls into carboxylate anions. The cations that were fixed are oxygenated and certainly contain calcium, but also uranium and perhaps several other cations (V, Mo, Fe...). Emphasis is placed on possible mechanisms that cause such phenomena.  相似文献   

Policy and implementation in rural planning     

Paul Cloke  Patrick Hanrahan 《Geoforum》1984,15(2):261-269

Although often critical of the results achieved by rural planners, research by geographers and others has for some time been constrained by an inability to isolate the precise impacts of planning procedures on rural areas. The notions of a technically solvable ‘implementation problem’ and a politically complex ‘policy problem’ are confronted here, and acknowledgement of the latter directs research into the realms of decision-making and policy-implementation iteration in rural areas. Key themes in the understanding of these matters are those of central-local state relations, inter-agency relations and public-private sector relations, all of which should figure prominently in any conceptualisation of policymaking and implementation in rural areas. One final factor which invites conceptual clarification is that of the specificity of rurality as a policy-moulding phenomenon. The idea is introduced of a ‘rural dimension’ which presents a spatial facade to aspatial structures and processes.  相似文献   

A modified parameterization of flux-profile relationships in the surface layer using different roughness length values for heat and momentum   总被引：1，自引：0，他引：1  

Patrick Mascart  Joel Noilhan  Hervé Giordani 《Boundary-Layer Meteorology》1995,72(4):331-344

The surface-layer flux-profile formulae of Louis (1979), used in many atmospheric models, are modified in a simple way to allow for different values of the roughness lengths for heat and momentum. The modified set of formulae simplifies the calculation of surface-layer fluxes over most natural land surfaces, where the roughness length for momentum can be almost an order of magnitude greater than that for heat.  相似文献   

Some Biases in Sampling Multilevel Piezometers for Volatile Organics     

J. F. Barker  G. C Patrick  L. Lemon  G. M. Travis 《Ground Water Monitoring & Remediation》1987,7(2):48-54

Multilevel piezometers are cost-effective monitoring devices for determining the three-dimensional distribution of solutes in ground water. Construction includes flexible tubing (plastic or Teflon®). Their sampling is subject to a number of'potential biases, particularly: (1) losses of volatile organic solutes via volatilization, (2) sorption onto the flexible tubing of the piezometers, (3) leaching of organics from this tubing, and (4) collection of unrepresentative samples due to inadequate piezometer flushing. It is shown that these biases are minimal or are easily controlled in most situations.
Another source of bias has been recognized. Organic solutes present in ground water above the screened level can penetrate the flexible plastic or Teflon tubing and contaminate the sampled water being drawn through this tubing. Laboratory tests and field results indicate this transmission causes low organic contaminant concentrations to be erroneously attributed to ground water which is free of such contaminants. The transmitted organics apparently desorb from the plastic tubing during flushing of even 40 piezometer volumes.
Recognition of this transmission problem provides for a better interpretation of existing organic contaminant distribution data. Caution is advised when considering the use of these monitoring devices in organic solute contaminant studies.  相似文献