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21.
Precipitation stable isotope variability and subcloud evaporation processes in a semi‐arid region 
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下载免费PDF全文 The stable isotopic (2H/1H and 18O/16O) composition of precipitation has been used for a variety of hydrological and paleoclimate studies, a starting point for which is the behaviour of stable isotopes in modern precipitation. To this end, daily precipitation samples were collected over a 7‐year period (2008–2014) at a semi‐arid site located at the Macquarie Marshes, New South Wales (Australia). The samples were analysed for stable isotope composition, and factors affecting the isotopic variability were investigated. The best correlation between δ 18O of precipitation was with local surface relative humidity. The reduced major axis precipitation weighted local meteoric water line was δ 2H = 7.20 δ 18O + 9.1. The lower slope and intercept (when compared with the Global Meteoric Water Line) are typical for a warm dry climate, where subcloud evaporation of raindrops is experienced. A previously published model to estimate the degree of subcloud evaporation and the subsequent isotopic modification of raindrops was enhanced to include the vertical temperature and humidity profile. The modelled results for raindrops of 1.0 mm radius showed that on average, the measured D‐excess (=δ 2H ? 8 δ 18O) was 19.8‰ lower than that at the base of the cloud, and 18% of the moisture was evaporated before ground level (smaller effects were modelled for larger raindrops). After estimating the isotopic signature at the base of the cloud, a number of data points still plotted below the global meteoric water line, suggesting that some of the moisture was sourced from previously evaporated water. Back trajectory analysis estimated that 38% of the moisture was sourced over land. Precipitation samples for which a larger proportion of the moisture was sourced over land were 18O and 2H‐enriched in comparison to samples for which the majority of the moisture was sourced over the ocean. The most common weather systems resulting in precipitation were inland trough systems; however, only East Coast Lows contributed to a significant difference in the isotopic values. Copyright © 2016 Australian Nuclear Science and Technology Organisation. Hydrological Processes. © 2016 John Wiley & Sons, Ltd. 相似文献
22.
Jordan S. Oestreicher Karina Benessaiah Maria C. Ruiz-Jaen Sean Sloan Kate Turner Johanne Pelletier Bruno Guay Kathryn E. Clark Dominique G. Roche Manfred Meiners Catherine Potvin 《Global Environmental Change》2009,19(2):279-291
Reducing greenhouse gas emissions from deforestation and forest degradation (REDD) is likely to be central to a post-Kyoto climate change mitigation agreement. As such, identifying conditions and factors that will shape the success or failure of a reduced deforestation scheme will provide important insights for policy planning. Given that protected areas (PAs) are a cornerstone in forest conservation, we draw on interviews and secondary data to analyze the effects of available PA resources, governance ability, the level of community involvement, and provincial deforestation rates on land-cover change in nine PAs in Panama. Our results illustrate that coupling surveillance measures with greater funding and strong governance are paramount to reducing deforestation. Alone, however, these factors are insufficient for forest protection. We argue that conservation approaches that complement effective surveillance with community participation and equitable benefit sharing will address the wider issues of leakage and permanence. 相似文献
23.
Menone ML Miglioranza KS Botto F Iribarne O Aizpún de Moreno JE Moreno VJ 《Marine pollution bulletin》2006,52(12):1717-1724
The influence of intertidal crab beds on the concentrations of organochlorine (OC) pesticides in sediment was studied in two different coastal environments in Argentina. Samples of male burrowing crabs (Chasmagnathus granulatus) were collected for this study. Our field data showed lower bioaccumulation of OC pesticides in crabs from sediments with a higher total organic carbon (TOC) and higher clay content. Thus, concentrations in crabs depend on the physico-chemical characteristics of the sediment where they live more than on the OC pesticide concentrations in the environment. The distribution patterns in sediment from inside and outside crab burrows were similar for both coastal areas being HCHs γ-chlordane > p,p′-DDE for San Antonio Bay (SAO), and HCHs > p,p′-DDE γ-chlordane for Mar Chiquita (MCh) coastal lagoon. OC pesticide concentrations in sediment were significantly lower inside than outside crab burrows, irrespective of the sediment physico-chemical characteristics due to the bioturbation activity of C. granulatus. 相似文献
24.
Gabriel Katul Chun-Ta Lai Karina Schfer Brani Vidakovic John Albertson David Ellsworth Ram Oren 《Advances in water resources》2001,24(9-10)
The variability in land surface heat (H), water vapor (LE), and CO2 (or net ecosystem exchange, NEE) fluxes was investigated at scales ranging from fractions of seconds to years using eddy-covariance flux measurements above a pine forest. Because these fluxes significantly vary at all these time scales and because large gaps in the record are unavoidable in such experiments, standard Fourier expansion methods for computing the spectral and cospectral statistical properties were not possible. Instead, orthonormal wavelet transformations
are proposed and used. The
are ideal at resolving process variability with respect to both scale and time and are able to isolate and remove the effects of missing data (or gaps) from spectral and cospectral calculations. Using the
spectra, we demonstrated unique aspects in three appropriate ranges of time scales: turbulent time scales (fractions of seconds to minutes), meteorological time scales (hour to weeks), and seasonal to interannual time scales corresponding to climate and vegetation dynamics. We have shown that: (1) existing turbulence theories describe the short time scales well, (2) coupled physiological and transport models (e.g. CANVEG) reproduce the wavelet spectral characteristics of all three land surface fluxes for meteorological time scales, and (3) seasonal dynamics in vegetation physiology and structure inject strong correlations between land surface fluxes and forcing variables at monthly to seasonal time scales. The broad implications of this study center on the possibility of developing low-dimensional models of land surface water, energy, and carbon exchange. If the bulk of the flux variability is dominated by a narrow band or bands of modes, and these modes “resonate” with key state and forcing variables, then low-dimensional models may relate these forcing and state variables to NEE and LE. 相似文献
25.
Sediment cores from two locations in Green Bay and two in lake Michigan were analyzed for 12 polycyclic aromatic hydrocarbons (PAHs), loss-on-ignition (LOI),210Pb,137Cs, and7Be to study differences in deposition patterns between the freshwater estuary Green Bay, with several local sources, and the open Lake Michigan, dominated by atmospheric inputs. We found that the remote sites receive relatively less high-molecular weight PAHs such as ideno(1,2,3-cd)pyrene and dibenz(ah)anthracene and are more depleted in anthracene and pyrene. This may be related to a low Henry’s law constant for the high molecular compounds and to selective photo-oxidation of anthracene and pyrene during transport. While sedimentation rates are higher in Green Bay than in the open lake, the PAH levels are generally comparable (0.3–8.5 μg g?1) in the two areas. However, the highest PAH levels are found in a core from Green Bay (GB88G). The two Green Bay cores have total PAH concentration maxima in 1985, which appear to be related to the combustion of petroleum. Also, one Green Bay core (GB88G) and the two from Lake Michigan exhibit PAH maxima in the early 1950s in agreement with observations from other study areas. There is a significant correlation between total PAH and LOI, and thus total organic carbon, for the Green Bay cores, but little or no such correlation for the Lake Michigan cores. This may indicate that PAHs in Green Bay are effectively scavenged by settling detritus. 相似文献
26.
Karina Williams 《Astronomy& Geophysics》2006,47(3):3.36-3.37
Tiny black holes could be popping in and out of existence in our atmosphere all the time. It sounds a scary prospect but, as Karina Williams explains, there is (probably) no need to be alarmed. 相似文献
27.
Karina?L.?LecomteEmail author Andrea?I.?Pasquini Pedro?J.?Depetris 《Aquatic Geochemistry》2005,11(2):173-194
By means of PHREEQC inverse modeling, we have simulated the weathering reactions in Los Reartes River, a mountainous (2400–670 m a.s.l.) drainage basin from the Sierras Pampeanas of Córdoba, Argentina, analyzing the effect of lithology, relief, and climate. The steep upper half of the basin (slopes > 20) is occupied by exposed granite; the remaining area is mostly metamorphic, with cropping out gneisses and progressively decreasing slopes (< 6). Climate is semihumid to semiarid; rainfall mainly occurs in summer and decreases with decreasing height. PHREEQC inverse models developed using water chemical data showed that (a) oligoclase was the major supplier of solutes, while the main precipitated phase was kaolinite in the granite domain; (b) muscovite is the chief supplier of solutes and illite is the main precipitated phase in the gneissic realm; (c) the steeper portions of the metamorphic reach are less crucial in supplying solutes than the lower ones, thus highlighting the importance of the water residence time in the kinetics of dissolution; (d) in the driest time of the year (winter, 20 mm/month) we registered the highest production of dissolved and precipitated phases; fluxes (mmol/month), however, are higher at the end of the rainy season; (e) CO2 consumption is important all along the Los Reartes drainage basin and, in terms of mmol/kg H2O, the lowermost portion of the basin is the most significant supplier; (f) CO2 accounts for over 50 of all the species involved in the weathering reactions occurring at the Los Reartes drainage basin. 相似文献
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Flow cytometry was used to examine immune responses in haemocytes of the green-lipped mussel Perna viridis under six combinations of oxygen level (1.5 mg O2 l(-1), 6.0 mg O2 l(-1)) and temperature (20 °C, 25 °C and 30 °C) at 24 h, 48 h, 96 h and 168 h. The mussels were then transferred to normoxic condition (6.0 mg O2 l(-1)) at 20 °C for further 24 h to study their recovery from the combined hypoxic and temperature stress. Esterase (Est), reactive oxygen species (ROS), lysosome content (Lyso) and phagocytosis (Pha) were reduced at high temperatures, whereas hypoxia resulted in higher haemocyte mortality (HM) and reduced phagocytosis. For HM and Pha, changes were observed after being exposed to the stresses for 96 h, whereas only a 24 h period was required for ROS and Lyso, and a 48 h one for Est. Recovery from the stresses was observed for HM and Pha but not other immune responses. 相似文献
30.
Daniele Botelho de Souza Karina Scurupa Machado Sandro Froehner Cristóvão Fernandes Scapulatempo Tobias Bleninger 《Chemie der Erde / Geochemistry》2011,71(2):171-176
The geochemical composition of lake bed sediments of a tropical reservoir in Brazil have been investigated. The C, N, P composition showed almost no variation between the different sampling points. All samples contained inorganic phosphorus (IP) ranging from 52 to 70%. The Redfield ratios show that the lake is without significant anthropogenic inputs. Most of the organic matter is composed by higher plants decomposition revealed in the total organic carbon (TOC):nitrogen (N) ratio ranging from 15.4 to 57.2. Also, TOC:organic phosphorus (OP) ranged from 265.3 to 933.6, suggesting that most of the organic matter has terrestrial origin from wood plants. The ratios suggest that most organic matter is influenced by the terrestrial characteristics of the watershed. Furthermore, the relative abundance of n-alkane homologues in the sediments was investigated. All samples have been analyzed for the n-alkanes C8 to C40. The sediments were dominated by n-alkanes C25–C38. It is concluded that n-alkane in sediments mainly come from terrestrial plants, however there is a contribution of submerged aquatic plants, especially in those sites in deeper areas of the lake. On the basis of Paq index the n-alkanes in sediments comes from terrestrial plants, however there is a contribution from emerged/floating plants.The investigated lake seems to be considered as meso to eutrophic. Because of the relatively high primary productivity in the lakes, there is a substantial organic-matter flux to the sediments, which rapidly becomes anoxic. According to the pristine/phytane ratio the sediments represent an anoxic environment with values found between 0.38 and 1.72. 相似文献