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91.
Characterizing the spatial dynamics of soil moisture fields is a key issue in hydrology, offering an avenue to improve our understanding of complex land surface–atmosphere interactions. In this paper, the statistical structure of soil moisture patterns is examined using modelled soil moisture obtained from the North American Land Data Assimilation System (NLDAS) at 0.125° resolution. The study focuses on the vertically averaged soil moisture in the top 10 cm and 100 cm layers. The two variables display a weak dependence for lower values of surface soil moisture, with the strength of the relationship increasing with the water content of the top layer. In both cases, the variance of the soil moisture follows a power law decay as a function of the averaging area. The superficial layer shows a lower degree of spatial organization and higher temporal variability, which is reflected in rapid changes in time of the slope of the scaling functions of the soil moisture variance. Conversely, the soil moisture in the top 100 cm has lower variability in time and larger spatial correlation. The scaling of these patterns was found to be controlled by the changes in the soil water content. Results have implications for the downscaling of soil moisture to prevent model bias.  相似文献   
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We have developed a new technique to decouple the spectra of the host and the nucleus of type I AGNs using integral field spectroscopy data. The technique is a simple extension of methods widely tested in 2D imaging. We present here the results from applying the technique to data taken with INTEGRAL at the 4.2 m William Herschel Telescope on the Seyfert 1 radio-galaxy 3C 120. We obtained, for the first time, a clean spectrum of the host galaxy, without contamination from the nuclear source.  相似文献   
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The Bilbao Estuary is one of the most contaminated estuaries on the north coast of Spain, and vast efforts have been made to abate pollution there. In fact, the local water authority has forecast a biological recovery of the native fauna after a substantial increase in dissolved oxygen to normoxic levels. In order to assess this prediction by evaluating the extent of natural regeneration of these polluted sediments, two long-term bioassays (t=90 d) were performed. In both of them, lethal (differences in survival) and sublethal (differences in length and weight growth) effects were measured by using juvenile individuals of the autochthonous clam, Scrobicularia plana (Da Costa, 1778). The sediments tested differed in pollution levels, as measured by a set of indicators including PAHs, PCBs, heavy metals, volatile organic matter and coprostanol. All sediments were finally exposed to normoxic conditions in situ in the Bilbao Estuary (DO approximately 6.3 mg l(-1)). In the first experiment, concerning moderately polluted sediments from the Bilbao Estuary and reference sediments from the "pristine" Plentzia Estuary, no significant differences (P>0.05) were found regarding animal survival (approximately 94.5%) or growth in length or weight between the sediments tested. In the second experiment, also involving grossly polluted sediments (GPS) from the Bilbao Estuary, survival (24.5%) was statistically lower (P<0.05) than in the other sediments (approximately 93%). No significant differences were found in growth (length, weight) between animals exposed to moderately polluted or reference sediments. We interpret this dramatic difference in survival as the lethal effect on the animals tested of the GPS of the Bilbao Estuary, indicating a situation where biological recovery is not possible due to the adverse consequences of contaminants sorbed into sediments. The extensive use of this inexpensive bioassay could help to distinguish sediments in which homeostatic recovery is possible from grossly polluted "hot spots", which need costly remedial actions.  相似文献   
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In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean (36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L−1 in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems and ranged from 66 to 9,038 μg GX eq L−1. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes, the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column.  相似文献   
99.
The bioavailability and toxicity of copper (Cu) in Shelter Island Yacht Basin (SIYB), San Diego, CA, USA, was assessed with simultaneous toxicological, chemical, and modeling approaches. Toxicological measurements included laboratory toxicity testing with Mytilus galloprovincialis (Mediterranean mussel) embryos added to both site water (ambient) and site water spiked with multiple Cu concentrations. Chemical assessment of ambient samples included total and dissolved Cu concentrations, and Cu complexation capacity measurements. Modeling was based on chemical speciation and predictions of bioavailability and toxicity using a marine Biotic Ligand Model (BLM). Cumulatively, these methods assessed the natural buffering capacity of Cu in SIYB during singular wet and dry season sampling events. Overall, the three approaches suggested negligible bioavailability, and isolated observed or predicted toxicity, despite an observed gradient of increasing Cu concentration, both horizontally and vertically within the water body, exceeding current water quality criteria for saltwater.  相似文献   
100.
So far, six mechanisms have been proposed to account for the Galactic disc heating. Of these, the most important appear to be a combination of scattering of stars by molecular clouds and by spiral arms. We study a further mechanism, namely the repeated disc impact of the original Galactic globular cluster population up to the present. We find that globular clusters could have contributed at most a small fraction of the current vertical energy of the disc, as they could heat the whole disc to  σ z = 5.5 km s−1  (c.f. the observed 18 and 39 km s−1 for the thick and thin discs, respectively). We find that the rate of rise of disc heat (  α= 0.22  in  σ z ∼ t α  with t being time) is close to that found for scattering by molecular clouds.  相似文献   
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