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471.
Nitrogen and phosphorus content ofSpartina alterniflora Loisel and soil nitrogen were measured along a transect perpendicular to a stream in a Louisiana salt marsh in order to provide information on differences between the so-called streamside and inland regions. Total plant nitrogen and phosphorus levels in June and September tended to be greater at streamside than inland sites. Total soil nitrogen on a dry soil weight basis increased with distance inland from a natural stream toward an interdistributary basin in the marsh. Soil extractable ammonium-nitrogen levels measured in June were very low in vegetated streamside and inland areas, but they were much higher in inland areas devoid of plants. Nitrogen and phosphorus utilization byS. alterniflora was also investigated at an inland location in the salt marsh. Labelled ammonium-nitrogen and phosphate-phosphorus were added in May at a rate of 200 kg/ha to the soil of replicated plots. Added nitrogen significantly increased total above-ground plant biomass and plant height by 28 and 25%, respectively, 4 months after application. The ratio of belowground macro-organic matter to total aboveground biomass was decreased from 5.7 to 4.7 by the additional nitrogen. Added phosphorus did not significantly affect plant height and biomass. The use of15N-depleted nitrogen tracers showed that about half of the nitrogen in the aboveground portion ofS. alterniflora from 1 to 4 months after the nitrogen addition was derived from the added ammonium-nitrogen. After 4 months, 28 and 29% of the added labelled nitrogen was recovered in the aboverground and belowground biomass ofS. alterniflora, respectively. Recovery of added nitrogen was overestimated with a non-tracer method based on the difference in total nitrogen uptake between nitrogen-amended plots and untreated plots. Soil organic nitrogen comprised the majority of the nitrogen in the salt marsh. Nitrogen in the standing crop biomass ofS. alterniflora represented only about 2% of the total nitrogen in the plantsoil system of an inland marsh to a 20 cm soil depth. 相似文献
472.
Sources and transport of carbon and nitrogen in the River Sava watershed, a major tributary of the River Danube 总被引:1,自引:0,他引:1
Nives Ogrinc Roland Markovics Tjaa Kandu
Lynn M. Walter Stephen K. Hamilton 《Applied Geochemistry》2008,23(12):3685-3698
Carbon and nitrogen dynamics were examined throughout the River Sava watershed, a major tributary of the River Danube, in 2005 and 2006. The River Sava exported 2.1 × 1011 mol C/yr as dissolved inorganic carbon (DIC), and emitted 2.5 × 1010 mol C/yr as CO2 to the atmosphere. Stable carbon isotope ratios indicate that up to 42% of DIC originated from carbonate weathering and 23% from degradation of organic matter. Loads of dissolved and particulate organic carbon increased with discharge and export rates were calculated to be 2.1 × 1010 mol C/yr and up to 4.1 × 109 mol C/yr, respectively. Isotopic compositions (δ13C and δ15N) and C/N ratios indicated that soil organic matter was the dominant source of particulate organic matter for 59% of the samples. Eighteen percent of the samples were dominated by plankton, 12% by periodic inputs of fresh terrestrial plant detritus with C/N > 15, and about 11% of the samples were dominated by the contribution of aquatic vascular plants. Nitrate inputs were controlled by land use in the River Sava watershed. δ15NNO3 values <6‰ were found in predominantly forested watersheds, while values >6‰ typically represented watersheds with a higher percentage of agricultural and/or urban land use. Elevated δ15NNO3 values (up to +25.5‰) at some sites were probably due to the combined effects of low-flow and inputs from sewage and/or animal waste. 相似文献
473.
Radio-isotopic analysis of single zircons from two early Telychian K-bentonites, one of which is among the most widespread Lower Paleozoic volcanic ash falls in north- ern Europe, yields overlapping weighted mean 206pb/238U ages of 438. 7± 1.0 Ma and 437.8 ± 0.5 Ma, respectively. The former age is from zircons of the Osmundsberg K-bentonite from the type locality at Osmundsberget in the Siljan area of central Sweden where it occurs in the lower part of the Spirograptus tur- riculatus Graptolite Zone and in the lower part of the Angochitina longicollis Chitinozoan Zone. Zircons giv- ing the latter age are from a bed previously identified as the Osmundsberg K-bentonite at the Kallholn Quarry in the same area. Based on new biostratigraphic data, the latter bed is now considered to be slightly younger than the Osmundsberg K-bentonite. The dated stratigraphic level of the ash layers is slightly younger than the base of the Telychian Stage and thus represents a minimum age for the Aeronian/Telychian Stage boundary. A U-Pb age of 〉 438 Ma for the base of this stage, however, is older and in conflict with estimates in the most recent compilation of the Silurian time scale. In view of the fact that only three radio-isotopic dates from the entire Llan- dovery have been previously accepted, this new and biostratigraphically exceptionally well-controlled radio-isotopic date fills an important gap in the Lower Silurian geochronology. 相似文献
474.
475.
Monitoring drilling deviation is important for drilling of boreholes and measuring injection rock permeability by Lugeon value for safe and efficient drilling and grouting. This paper is aiming at the study drilling deviation and relationship between drilling and injection permeability at the depth of 100 m in dam of Pushi River. The results show that at different depths the deviation of grouting borehole is within the allowable range according to specifications. LU value decreases with the depth increased in general, but at the depths between 40-41 m the permeability is 1.5 LU, and at 24 m the LU value is the largest (2 LU) in this site by this study. The study thus concludes that even though the rocks are hard and their injection permeability decreases with depth increased, good drilling practices including carefully considering technical and geological specifications can get good drilling boreholes. 相似文献
476.
Trine Marianne Holm Karin A. Koinig Tom Andersen Espen Donali Anne Hormes Dag Klaveness Roland Psenner 《Aquatic Sciences - Research Across Boundaries》2012,74(3):385-395
High Arctic lakes are among the most sensitive ecosystems and climate change strongly affects their physical properties, especially water temperature, and mixing processes. To study the effect of recent climate change on such a lake in the Arctic environment, we measured water chemistry and temperature from 2005 to 2010 in Kongressvatn, a crenogenic meromictic lake in Spitsbergen (Svalbard). In addition, we monitored water column temperatures during two consecutive years and compared them to regional air temperature data and physicochemical lake data from 1962 and 1968, two relatively cold years. Summer surface water temperature was highly correlated to air temperature, and both have increased by approximately 2°C since 1962. Temperature monitoring during 2?years showed that the warm summer of 2007 resulted in increased water temperatures even in the stratified, denser hypolimnion. Our water chemistry measurements showed that the chemocline position in 2005?C2010 was ca 12?m deeper than in 1962?C1968, and a second, weaker, chemocline appeared at metalimnetic depths of 7?C15?m. During the study period, the water level decreased by 4?m, and this change accelerated between 2008 and 2010. Our data support the hypothesis that water temperatures and stratification patterns are changing rapidly with air temperature, but changes in the catchment, such as glacial retreat and permafrost melting, may have an even stronger impact on lake properties. 相似文献
477.
Nina Reuss Peter R. Leavitt Roland I. Hall Christian Bigler Dan Hammarlund 《Journal of Paleolimnology》2010,43(1):149-169
A surface-sediment survey of pigments in 100 lakes in the Scandes Mountains, northern Sweden, was combined with a reconstruction
of Holocene sedimentary pigments from Lake Seukokjaure to assess the major factors regulating phototrophic communities, and
how these controls may have changed during the period from the deglaciation (~9700 cal. years BP) to the present. The study
area covers a pronounced gradient of temperature and precipitation, and encompasses the subarctic tree line, an important
ecotonal boundary in this region. Lake Seukokjaure is located in a presently treeless basin close to the modern tree line.
The spatial survey of sedimentary pigments was analyzed using principle components analysis (PCA) and redundancy analysis
(RDA). PCA explained 73–83% of variance in pigment abundance and composition, whereas RDA explained 22–32% of variation in
fossil assemblages. Dissolved organic carbon (DOC) content of lake water, sediment δ13C, maximum lake depth, elevation and lake-water conductivity were all identified as environmental variables with significant
association with pigment abundances in the spatial survey, although phototrophic communities of lakes situated in different
vegetation zones (alpine, birch, conifer/birch) were incompletely distinguished by the ordinations. In the RDAs, the primary
pigment variability occurred along a production gradient that was correlated negatively to water-column DOC content and δ13C signature of sediments. This pattern suggested that the important controls of primary production were light regime and terrestrial
supplies of 13C-depleted carbon. In contrast, depth, elevation and conductivity were found to be more important for the differentiation
of the phototrophic community composition. Application of these spatial survey results to the Holocene sediment record of
Lake Seukokjaure demonstrated the importance of DOC for the temporal development of the lake, from an early state of high
production to a period of slight oligotrophication. In general, the algal changes were regulated by the interaction of DOC
and conductivity, although transitions in the phototrophic community during the late Holocene were less easily interpreted.
Terrestrial vegetation development thus appears to be of utmost importance for the regulation of primary production in oligotrophic
alpine and subarctic lakes and climate impacts on lakes, whereas other basin-specific factors may control the ontogeny of
algal community composition. 相似文献
478.
The challenges of a changing world, which are progressively threatening sustainable use of groundwater resources, can only be rationally and effectively addressed through close collaboration between experts and practitioners from different disciplines. Furthermore, science and management need to build on stakeholder opinions and processes in order to generate useful knowledge and positive outcomes in terms of sustainable and equitable groundwater management. This essay provides a discussion of the status of and vision for participatory and inter-disciplinary approaches to groundwater evaluation and management as well as a conceptual framework and relevant research questions that will facilitate such approaches. 相似文献
479.
Michael?A.?SokalEmail author Roland?I.?Hall Brent?B.?Wolfe 《Journal of Paleolimnology》2008,39(4):533-550
Water chemistry and surface sediments were analyzed from 41 shallow lakes representing three previously-defined hydrological
categories in the Slave River Delta, Northwest Territories, Canada, in order to identify relationships between hydrological
and limnological conditions and their associations with recently deposited diatom assemblages. Evaporation-dominated lakes are physically removed from the influence of the Slave River, and are characterized by high alkalinity and high concentrations
of nutrients and ions. In contrast, flood-dominated lakes tend to receive a pulse of floodwater from the Slave River during the spring thaw and have low alkalinity and low concentrations
of most nutrients and ions. Exchange-dominated lakes are variably influenced by floodwaters from the Slave River and seiche events from Great Slave Lake throughout the
spring thaw and open-water season, and are characterized by a broad array of limnological conditions that are largely dependent
on the strength of the connection to these sources of floodwater. Specific diatom ‘indicator’ taxa have been identified that
can discriminate these three hydrological lake categories. Evaporation-dominated lakes are associated with high relative abundance
of common epiphytic diatom taxa, while diatoms indicative of flood- and exchange-dominated lakes span a wide range of habitat
types (epiphytic, benthic) but also include unique planktonic diatoms (Stephanodiscus and Cyclostephanos taxa) that were not found in surface sediments of evaporation-dominated lakes. The planktonic diatom taxa originate from
the Slave River, and thus are indicative of river influence. In complex, remote, freshwater ecosystems like the Slave River
Delta, integration of results from hydrological and limnological approaches provides a necessary foundation to assess present,
past and future hydroecological responses to changes in river discharge and climate. 相似文献
480.
Annette T. Hollingshead Steven Businger Roland Draxler John Porter Duane Stevens 《Boundary-Layer Meteorology》2003,109(1):107-107