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241.
242.
Clayton J. Williams Rudolf Jaffé William T. Anderson Frank J. Jochem 《Estuarine, Coastal and Shelf Science》2009
A stable carbon isotope approach was taken to identify potential organic matter sources incorporated into biomass by the heterotrophic bacterial community of Florida Bay, a subtropical estuary with a recent history of seagrass loss and phytoplankton blooms. To gain a more complete understanding of bacterial carbon cycling in seagrass estuaries, this study focused on the importance of seagrass-derived organic matter to pelagic, seagrass epiphytic, and sediment surface bacteria. Particulate organic matter (POM), seagrass epiphytic, seagrass (Thalassia testudinum) leaf, and sediment surface samples were collected from four Florida Bay locations with historically different organic matter inputs, macrophyte densities, and primary productivities. Bulk (observed and those reported previously) and compound-specific bacterial fatty acid δ13C values were used to determine important carbon sources to the estuary and benthic and pelagic heterotrophic bacteria. The δ13C values of T. testudinum green leaves with epiphytes removed ranged from −9.9 to −6.9‰. Thalassia testudinum δ13C values were significant more enriched in 13C than POM, epiphytic, and sediment samples, which ranged from −16.4 to −13.5, −16.2 to −9.6, and −16.7 to −11.0‰, respectively. Bacterial fatty acid δ13C values (measured for br14:0, 15:0, i15:0, a15:0, br17:0, and 17:0) ranged from −25.5 to −8.2‰. Assuming a −3‰ carbon source fractionation from fatty acid to whole bacteria, pelagic, epiphytic, and sediment bacterial δ13C values were generally more depleted in 13C than T. testudinum δ13C values, more enriched in 13C than reported δ13C values for mangroves, and similar to reported δ13C values for algae. IsoSource mixing model results indicated that organic matter derived from T. testudinum was incorporated by both benthic and pelagic bacterial communities, where 13–67% of bacterial δ13C values could arise from consumption of seagrass-derived organic matter. The IsoSource model, however, failed to discriminate clearly the fraction of algal (0–86%) and mangrove (0–42%) organic matter incorporated by bacterial communities. These results indicate that pelagic, epiphytic, and sediment surface bacteria consumed organic matter from a variety of sources. Bacterial communities incorporated consistently seagrass-derived organic matter, the dominant macrophyte in Florida Bay, but seagrass δ13C values alone could not account fully for bacterial δ13C values. 相似文献
243.
Rudolf Brázdil Zdeněk Máčka Ladislava Řezníčková Eva Soukalová Petr Dobrovolný Tomáš Matys Grygar 《水文科学杂志》2013,58(7):1166-1185
Abstract The development of the River Morava floodplain has been influenced by several natural and anthropogenic factors. This paper focuses on variations in flood activity and channel changes of the River Morava in the region of Strá?nické Pomoraví (southeastern Czech Republic). Floods are analysed in terms of measured peak water stages, Hk (Rohatec, 1886–1920) and peak discharges Qk (Rohatec/Strá?nice, 1921–2010) evaluated with respect to their N-year return period (H N or QN ). The frequency of floods with Qk ≥ Q 2 reaches a significant maximum in March, followed by July. According to flood series compiled from 1881 onwards, their frequency peaked in the 1961–1970 decade with the most severe events occurring in July 1997 (Q 100), March 2006 and June 2010 (Q 50). During the study period the natural dynamics of the original anabranching channel patterns were significantly modified by human intervention, such as the abandonment of some anabranching channels, channel straightening, enlargement of the main channel, flood-dike construction, and the creation of the Ba?a shipping channel. These changes resulted in decreased frequency and a reduction in the extent of floodplain inundations compared to the period prior to channel modifications in the 1930s. Citation Brázdil, R., Má?ka, Z., ?ezní?ková, L., Soukalová, E., Dobrovolný, P. & Matys Grygar, T. (2011) Floods and floodplain changes of the River Morava, the Strá?nické Pomoraví region (Czech Republic) over the past 130 years. Hydrol. Sci. J. 56(7), 1166–1185. 相似文献
244.
Á. Bazsó R. Dvorak E. Pilat-Lohinger V. Eybl Ch. Lhotka 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):63-76
It is known since the seminal study of Laskar (1989) that the inner planetary system is chaotic with respect to its orbits and even escapes are not impossible, although in time scales of billions of years. The aim of this investigation is to locate the orbits of Venus and Earth in phase space, respectively, to see how close their orbits are to chaotic motion which would lead to unstable orbits for the inner planets on much shorter time scales. Therefore, we did numerical experiments in different dynamical models with different initial conditions—on one hand the couple Venus–Earth was set close to different mean motion resonances (MMR), and on the other hand Venus’ orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i = 40°). The couple Venus–Earth is almost exactly in the 13:8 mean motion resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8 resonance are within a small shift in the Earth’s semimajor axis (only 1.5 percent). Especially Mercury is strongly affected by relatively small changes in initial eccentricity and/or inclination of Venus, and even escapes for the innermost planet are possible which may happen quite rapidly. 相似文献
245.
Environmental fate of fish farm wastes (FFW) released from an open-sea-cage farm at Kat O, Hong Kong was examined by measuring carbon and nitrogen stable isotope (SI) ratios in selected benthic organisms collected along a 2000 m transect from the farm. Our results showed that FFW significantly influenced the energy utilization profile of consumers near the fish farm. Although nitrogen enrichment effect on δ15N was anticipated in biota near the farm, the predicted patterns did not consistently occur in all feeding guilds. Two species of suspension-feeders, which relied on naturally δ15N-depleted sources, were δ15N-enriched near the fish farm. In contrast, both species of benthic grazer and deposit-feeder, which relied on naturally δ15N-enriched algal sources, were δ15N-depleted under the influence of FFW. The SI signatures of biota can, therefore, serve as feasible biomarkers for FFW discharges only when the trophic structure of the receiving environment is fully elucidated. 相似文献
246.
Youhei?YamashitaEmail author Anouska?Panton Claire?Mahaffey Rudolf?Jaffé 《Ocean Dynamics》2011,61(5):569-579
The spatial and diurnal tidal variability of dissolved organic carbon (DOC) concentrations and the composition of dissolved
organic matter (DOM), as evaluated by high-temperature catalytic oxidation and excitation–emission matrix combined with parallel
factor analysis (EEM–PARAFAC), respectively, were determined in Liverpool Bay. EEM–PARAFAC modeling resulted in six fluorescent
components characterized as terrestrial humic-like (two), microbial humic-like (two), and protein-like (two). The spatial
distributions of DOC and the four humic-like components were negatively correlated with salinity in the high-salinity waters
observed in this study (30.41–33.75), suggesting that terrestrial DOM was conservatively distributed. The spatial patterns
of protein-like components were largely different from those of DOC, humic-like components, and chlorophyll a, suggesting that these distributions were the combined result of production and degradation in the bay in addition to river
inputs. These findings suggest that the DOM dynamics in Liverpool Bay are strongly controlled by river-dominated allochthonous
DOM inputs with some less significant contributions of autochthonous DOM within the bay. In addition, the temporal variations
of DOM associated with the diurnal tidal cycles were determined at one inshore (31.34–32.24 salinity) and one offshore (33.64–33.75
salinity) station in the bay. Negative linear relationships between salinity and DOM characteristics, i.e., DOC, humic-like,
and protein-like components, were observed at the inshore station. In contrast, no relationship was observed at the offshore
station, suggesting that the export of DOM through rivers and possibly tidal flats have a noticeable influence on DOM concentration
and composition up to a relatively elevated salinity of around 33 in Liverpool Bay. 相似文献
247.
Several new radiation defects with total electron spin S?=?1 occurring in electron-irradiated, synthetic ??-quartz have been observed by using electron paramagnetic resonance spectroscopy. These defects are considered to be biradicals, i.e., pairs of S?=?1/2 species. The concentration of these centers depends on the condition of the fast-electron irradiation. They have different decay behaviors that allow measurements of any individual species especially when it predominates over the others. The primary spin Hamiltonian parameter matrices g 1, g 2, D have now been determined for two similar defects, which herein are labeled $ E_{2}^{\prime \prime } $ and $ E_{4}^{\prime \prime } $ . Inter-electron distances estimated by using the magnetic dipole model, suggest that the structures of centers $ E_{2}^{\prime \prime } $ and $ E_{4}^{\prime \prime } $ both involve the unpaired electrons each located in orbitals of two silicon atoms next to a common oxygen vacancy but which have slightly different Si?CSi distances at 0.90 and 0.79?nm, respectively. This model is consistent with previous DFT calculations of the triplet configurations with local energetic minima. Observed decay behaviors suggest a transformation of centers $ E_{2,4}^{\prime \prime } $ to the analogous $ E_{1}^{\prime \prime } $ center. These triplet centers in quartz provide new insights into the structures of analogous defects in amorphous silica. 相似文献
248.
Petr Kolář Miroslav Trnka Rudolf Brázdil Petr Hlavinka 《Theoretical and Applied Climatology》2014,117(3-4):707-721
The paper aims to study the variability of spring barley and winter wheat yields, the most important crops in the Czech Republic, with respect to the variability of weather and climatic factors. Yields of both crops have been studied for 13 districts in Southern Moravia for the 1961–2007 period. From detrended series of spring barley and winter wheat yields, years with very low (lower than the mean minus a 2.5-multiple of the standard deviation) and extremely low (interval given by the mean minus a 1.5- and 2.5-multiple of the standard deviation) yields were selected. Years in which at least one of the districts had extremely low/very low yields were further analyzed. From 10 such years selected separately for spring barley and winter wheat, six of them agreed for both crops. Extreme years were studied using NUTS4-level yield data with respect to temperature, precipitation, the self-calibrated Palmer Drought Severity Index (scPDSI), snow cover, frost patterns, and the onset and duration of select phenophases. Extremely/very low barley yields in 1993, 2000, and 2007 were related to high April–June (AMJ) temperatures, low AMJ precipitation totals, and negative AMJ scPDSI (indicating drought) with an earlier onset of flowering and full ripeness and shorter intervals from tillering to flowering and from flowering to full ripeness compared to the entire 1961–2007 mean. As for extremely/very low winter wheat yields, in addition to the previously mentioned factors, winter patterns also played an important role, particularly the occurrence of severe frosts with a coinciding lack of snow cover and a long-lasting snow cover (in highlands), indicating that low yields are the result of not only one unfavorable factor but a combination of several of them. 相似文献
249.
Richard Schwarz Markus Gyergyovits Rudolf Dvorak 《Celestial Mechanics and Dynamical Astronomy》2004,90(1-2):139-148
The orbits of real asteroids around the Lagrangian points L4 and L 5of Jupiter with large inclinations (i > 20°) were integrated for 50 Myrs. We investigated the stability with the aid of the
Lyapunov characteristic exponents (LCE) but tested also two other methods: on one hand we integrated four neighbouring orbits
for each asteroid and computed the maximum distance in every group, on the other hand we checked the variation of the Delaunay
element H of the asteroid. In a second simulation – for a grid of initial eccentricity versus initial inclination – we examined the
stability of the orbits around both Lagrangian points for 20° < i < 55° and 0.0 < e < 0.20. For the initial semimajor axes
we have chosen the one ofJupiter(a = 5.202 AU). We determined the stability with the aid of the LCEs and also the maximum
eccentricity of the orbits during the whole integration time. The region around L4 turned out to be unstable for large inclinations and eccentricities (i > 55° and e > 0.12). The stable region shrinks for
orbits around L5: we found that they become unstable already for i > 45° and e > 0.10. We interpret it as a first hint why we observe more
Trojans around the leading Lagrangian point. The results confirm the stability behaviour of the real Trojans which we computed
in the first part of the paper. 相似文献
250.