Effects of salinity on NH4 + adsorption capacity, nitrification, and denitrification in Danish estuarine sediments   总被引：1，自引：0，他引：1  

Søren Rysgaard  Peter Thastum  Tage Dalsgaard  Peter Bondo Christensen  Niels P. Sloth 《Estuaries and Coasts》1999,22(1):21-30

The regulatory effect of salinity on nitrogen dynamics in estuarine sediments was investigated in the Randers Fjord estuary, Denmark, using sediment slurries and intact sediment cores and applying ¹⁵N-isotope techniques. Sediment was sampled at three representative stations varying in salinity, and all experiments were run at 0‰, 10‰, 20‰, and 30‰. The sediment NH₄ ⁺ adsorption capacity decreased markedly at all stations when salinity was increased from 0‰ to 10‰; further increase showed little effect. In situ nitrification and denitrification also decreased with increasing salinities, with the most pronounced reduction of approximately 50% being observed when the salinity was raised from 0‰ to 10‰. The salinity-induced reduction in NH₄ ⁺ adsorption capacity and stimulation of NH₄ ⁺ efflux has previously been argued to cause a reduction in nitrification activity since the nitrifying bacteria become limited by NH₄ ⁺ availability at higher salinities. However, using a potential nitrification assay where NH₄ ⁺ was added in excess, it was demonstrated that potential nitrification activity also decreased with increasing salinity, indicating that the inhibitory salinity effect may also be a physiological effect on the microorganisms. This hypothesis was supported by the finding that denitrification based on NO₃ ⁻ from the overlying water (D_w), which is independent of the nitrification process, and hence NH₄ ⁺ availability, also decreased with increasing salinity. We conclude that changes in salinity have a significant effect on nitrogen dynamics in estuarine sediments, which must be considered when nitrogen transformations are measured and evaluated.  相似文献   

The use of proxy chemical records in Coral skeletons to ascertain past environmental conditions in Florida Bay     

Peter Koenraad Swart  Genevieve Healy  Lisa Greer  Michael Lutz  Amel Saied  Daniel Anderegg  Richard E. Dodge  David Rudnick 《Estuaries and Coasts》1999,22(2):384-397

This paper will discuss the use of chemical proxies in coral skeletons to reconstruct the history of salinity (from the δ¹⁸O of the skeleton) and nutrients in the water (from the δ¹³C) in Florida Bay between 1824 and 1994. Monthly salinity and water temperature data collected since 1989 were used to establish a correlation between salinity, temperature, and the δ¹⁸O of the skeleton of the coralSolenastrea bournoni from Lignumvitae Basin in Florida Bay. This relationship explains over 50% of the variance in the δ¹⁸O of the skeleton. Assuming that interannual variations in the temperature of the water are small, we have applied this relationship to the δ¹⁸O measured in the coral skeleton collected from Lignumvitae Basin which has a record between 1824 and 1993. These data provide a revised estimate of salinity variation in Lignumvitae Basin for the period when historical records for salinity were not available, and show that the highest salinity events occurred in the past 30 yr. Using the relationships between the salinity in Lignumvitate Basin and other basins, obtained using a modern dataset, we are able to estimate ranges in salinity for other portions of Florida Bay. Skeletons of specimens of the coral speciesSiderastrea radians collected from other areas of Florida Bay show similar patterns in the δ¹⁸O over the past 10 yr, indicating that corals in most portions of Florida Bay are recording salinity variations in their skeletons and therefore support the idea that salinity variations in different portions of Florida Bay can be related. Fluorescence analysis of the coral from Lignumvitae Basin shows a large change in the magnitude of the 10-yr signal coincident with the construction of the railway, confirming that this event had a significant impact upon Florida Bay. The δ¹³C of the coral skeletons reveals a long-term history of the oxidation of organic material, fixation of carbon by photosynthesis (algal blooms), and the intrusion of marine water into the bay. Since the construction of the railway from Miami to Key West there has been a long-term decrease in the δ¹³C of the coral skeleton from Lignumvitae Basin, suggesting the increased oxidation of organic material in this area. This decrease in δ¹³C appears to have reached a minimum value around 1984 and has increased since this time in the western portions of Florida Bay. The increase may be related to the algal blooms prevalent in the area or alternatively could result from intrusion of more marine water. In the eastern areas, a small increase in the δ¹⁸C between 1984 and 1988 was followed by further decline suggesting more oxidation of organic material. We have also attempted to use the concentration of barium in the coral skeleton as a proxy indicator of the nutrient status in Florida Bay.  相似文献   

Evidence for MTBE in Heating Oil     

Gary A. Robbins  Brent J. Henebry  Barbara M. Schmitt  Frank B. Bartolomeo  Aaron Green  Peter Zack 《Ground Water Monitoring & Remediation》1999,19(2):65-69

"Contamination of heating oil with MTBE could result in increasing the environmental impact of subsurface heating oil releases."  相似文献   

Constraints from high-pressure veins in eclogites on the composition of hydrous fluids in subduction zones   总被引：3，自引：0，他引：3  

Harry Becker  Klaus Peter Jochum  Richard W. Carlson 《Chemical Geology》1999,160(4):1207-308

Hydrous high-pressure veins formed during dehydration of eclogites in two paleo-subduction zones (Trescolmen locality in the Adula nappe, central Alps and Münchberg Gneiss Massif, Variscan fold belt, Germany) constrain the major and trace element composition of solutes in fluids liberated during dehydration of eclogites. Similar initial isotopic compositions of veins and host eclogites at the time of metamorphism indicate that the fluids were derived predominantly from the host rocks. Quartz, kyanite, paragonite, phengite, zoisite and omphacite are the dominant minerals in the veins. The major element compositions of the veins are in agreement with experimental evidence indicating that the composition of solutes in such fluids is dominated by SiO₂ and Al₂O₃. Relative to N-MORB, the veins show enrichments of Cs, Rb, Ba, Pb, and K, comparable or slightly lower abundances of Sr, U, and Th, and very low abundances of Nd, Sm, Zr, Nb, Ti and Y. The differential fractionation of highly incompatible elements such as K, U and Th in the veins, as well as the presence of hydrous minerals in the eclogites rule out partial melting as a cause for vein formation. These results confirm previous suggestions that fluids derived from subducted basalt may have low abundances of high field strength elements, rare earth elements and Y. Variable vein-eclogite enrichment factors of incompatible alkalis and to a lesser extent Pb appear to reflect mineralogical controls (phengite, epidote-group minerals) on partitioning of these elements during dehydration of eclogite in subduction zones. However, abundance variations of incompatible elements in minerals from eclogites suggest that the composition of fluids released from eclogites at temperatures <700°C may not reflect true equilibrium partitioning during dehydration. Simple models for the trace elements U and Th indicate the relative importance of the basaltic and sedimentary portions of subducted oceanic crust in producing the characteristic chemical signatures of these elements in convergent plate margin volcanism.  相似文献   

Volcanoes and peat bogs   总被引：1，自引：0，他引：1  

Jane Holmes  Valerie Hall  & Peter Wilson 《Geology Today》1999,15(2):60-63

Peat bogs in the British Isles contain tephra from volcanic eruptions in Iceland; tephra in the Falkland Islands most likely derives from Andean volcanoes. Study of these far-travelled volcanic products is making a significant contribution to our understanding of past environmental changes.  相似文献   

The Asia-Pacific Rim's transport and telecommunications systems: spatial structure and corporate control since the mid-1980s     

Peter J. Rimmer 《GeoJournal》1999,48(1):43-65

There is a need to move from discussing the Asia-Pacific Rim's leading port cities as shipping centres measured by container throughput. This shift in focus involves examining how different transport and telecommunications systems are interacting with each other at an international scale under the power and control of major world operators. Using a three-level network framework an attempt is made to illustrate and explain the formation of multilayered trade/communications corridors and hubs/headquarters in the Asia-Pacific Rim since the mid-1980s and to identify the factors affecting them. From this examination of spatial structure and corporate control three levels of cities in the Asia-Pacific Rim are recognised: first level cities with strong corporate representation in container shipping, air cargo, air passenger and telecommunications; second level cities with marked corporate representation in one but not all four modes; and third level cities with no marked corporate representation in any mode but with strong throughput. The third level includes the Asia-Pacific Rim's ‘true’ port cities. Perhaps the ambiguous category ‘port city’ should be reserved for them. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Reply     

Rebecca J. Dorsey  & Peter D. Falk 《Sedimentology》1999,46(4):763-767

  相似文献   

Tectonothermal history of the basement rocks in the western zone of the North China Craton and its tectonic implications   总被引：47，自引：0，他引：47  

Guochun Zhao  Simon A. Wilde  Peter A. Cawood  Liangzhao Lu 《Tectonophysics》1999,310(1-4):37-53

The basement of the North China Craton can be divided into the eastern, central and western zones, based on lithological, structural, metamorphic and geochronological data. The western zone comprises two different petrotectonic units: Archaean tonalitic–trondhjemitic–granodioritic (TTG) grey gneisses and metamorphic mafic rocks, and Palaeoproterozoic khondalite series. The former is characterized by isobaric cooling (IBC)-type anticlockwise P–T paths in the north-northwestern part of the zone and near-isothermal decompression (ITD)-type clockwise P–T paths in the eastern part, adjacent to the central zone. On the other hand, the tectonothermal evolution of Palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling, defining clockwise P–T paths. The Archaean TTG gneisses and associated mafic rocks with anticlockwise metamorphic P–T paths reflects an origin related to underplating and intrusion of mantle-derived magmas which may be derived from mantle plumes. They represent a late Archaean continental block in the western part of the North China Craton. The Palaeoproterozoic khondalite series rocks represent passive continental margin deposits. They were metamorphosed and deformed in the late Palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the North China Craton. The ITD-type clockwise P–T–t paths of the Palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the North China Craton at c. 1800 Ma.  相似文献   

Role of coal type and rank on methane sorption characteristics of Bowen Basin, Australia coals   总被引：5，自引：0，他引：5  

Chikatamarla Laxminarayana  Peter J. Crosdale 《International Journal of Coal Geology》1999,40(4):157

The effect of coal composition, particularly the organic fraction, upon gas sorption has been investigated for Bowen Basin and Sydney Basin, Australia coals. Maceral composition influences on gas retention and release were investigated using isorank pairs of hand-picked bright and dull coal in the rank range of high volatile bituminous (0.78% R_{o max}) to anthracite (3.01% R_{o max}). Adsorption isotherm results of dry coals indicated that Langmuir volume (V_L) for bright and dull coal types followed discrete, second-order polynomial trends with increasing rank. Bright coals had a minimum V_L at 1.72% R_{o max} and dull coals had a minimum V_L at 1.17% R_{o max}. At low rank, V_L was greater in bright coal by about 10 cm³/g, but as rank increased, the bright and dull trends converged and crossed at 1.65% R_{o max}. At ranks higher than 1.65% R_{o max}, both bright and dull coals followed similar trends. These competing trends mean that the importance of maceral composition on V_L varies according to rank. In high volatile bituminous coals, increases in vitrinite content are associated with increases in adsorption capacity. At ranks higher than medium to low volatile bituminous, changes in maceral composition may exert relatively little influence on adsorption capacity. The Langmuir pressure (P_L) showed a strong relationship of decreasing P_L with increasing rank, which was not related to coal type. It is suggested that the observed trend is related to a decrease in the heterogeneity of the pore surfaces, and subsequent increased coverage by the adsorbate, as coal rank increases. Desorption rate studies on crushed samples show that dull coals desorb more rapidly than bright coals and that desorption rate is also a function of rank. Coals of lower rank have higher effective diffusivities. Mineral matter was found to have no influence on desorption rate of these finely crushed samples. The evolution of the coal pore structure with changing rank is implicated in diffusion rate differences.  相似文献   

Development of an operational low-flow index for hydrological drought monitoring over Europe   总被引：1，自引：1，他引：0  

Carmelo Cammalleri  Jürgen Vogt  Peter Salamon 《水文科学杂志》2017,62(3):346-358

Near real-time monitoring of hydrological drought requires the implementation of an index capable of capturing the dynamic nature of the phenomenon. Starting from a dataset of modelled daily streamflow data, a low-flow index was developed based on the total water deficit of the discharge values below a certain threshold. In order to account for a range of hydrological regimes, a daily 95th percentile threshold was adopted, which was computed by means of a 31-day moving window. The observed historical total water deficits were statistically fitted by means of the exponential distribution and the corresponding probability values were used as a measure of hydrological drought severity. This approach has the advantage that it directly exploits daily streamflow values, as well as allowing a near real-time update of the index at regular time steps (i.e. 10 days, or dekad). The proposed approach was implemented on discharge data simulated by the LISFLOOD model over Europe during the period 1995–2015; its reliability was tested on four case studies found within the European drought reference database, as well as against the most recent summer drought observed in Central Europe in 2015. These validations, even if only qualitative, highlighted the ability of the index to capture the timing (starting date and duration) of the main historical hydrological drought events, and its good performance in comparison with the commonly used standardized runoff index (SRI). Additionally, the spatial evolution of the most recent event was captured well in a simulated near real-time test case, suggesting the suitability of the index for operational implementation within the European Drought Observatory.  相似文献