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61.
Interpreting the dependence of soil respiration on soil temperature and water content in a boreal aspen stand 总被引:8,自引:2,他引:8
David Gaumont-Guay T. Andrew Black Tim J. Griffis Alan G. Barr Rachhpal S. Jassal Zoran Nesic 《Agricultural and Forest Meteorology》2006,140(1-4):220
Continuous half-hourly measurements of soil CO2 efflux made between January and December 2001 in a mature trembling aspen stand located at the southern edge of the boreal forest in Canada were used to investigate the seasonal and diurnal dependence of soil respiration (Rs) on soil temperature (Ts) and water content (θ). Daily mean Rs varied from a minimum of 0.1 μmol m−2 s−1 in February to a maximum of 9.2 μmol m−2 s−1 in mid-July. Daily mean Ts at the 2-cm depth was the primary variable accounting for the temporal variation of Rs and no differences between Arrhenius and Q10 response functions were found to describe the seasonal relationship. Rs at 10 °C (Rs10) and the temperature sensitivity of Rs (Q10Rs) calculated at the seasonal time scale were 3.8 μmol m−2 s−1 and 3.8, respectively. Temperature normalization of daily mean Rs (RsN) revealed that θ in the 0–15 cm soil layer was the secondary variable accounting for the temporal variation of Rs during the growing season. Daily RsN showed two distinctive phases with respect to soil water field capacity in the 0–15 cm layer (θfc, 0.30 m3 m−3): (1) RsN was strongly reduced when θ decreased below θfc, which reflected a reduction in microbial decomposition, and (2) RsN slightly decreased when θ increased above θfc, which reflected a restriction of CO2 or O2 transport in the soil profile.Diurnal variations of half-hourly Rs were usually out of phase with Ts at the 2-cm depth, which resulted in strong diurnal hysteresis between the two variables. Daily nighttime Rs10 and Q10Rs parameters calculated from half-hourly nighttime measurements of Rs and Ts at the 2-cm depth (when there was steady cooling of the soil) varied greatly during the growing season and ranged from 6.8 to 1.6 μmol m−2 s−1 and 5.5 to 1.3, respectively. On average, daily nighttime Rs10 (4.5 μmol m−2 s−1) and Q10Rs (2.8) were higher and lower, respectively, than the values obtained from the seasonal relationship. Seasonal variations of these daily parameters were highly correlated with variations of θ in the 0–15 cm soil layer, with a tendency of low Rs10 and Q10Rs values at low θ. Overall, the use of seasonal Rs10 and Q10Rs parameters led to an overestimation of daily ranges of half-hourly Rs (ΔRs) during drought conditions, which supported findings that the short-term temperature sensitivity of Rs was lower during periods of low θ. The use of daily nighttime Rs10 and Q10Rs parameters greatly helped at simulating ΔRs during these periods but did not improve the estimation of half-hourly Rs throughout the year as it could not account for the diurnal hysteresis effect. 相似文献
62.
Background, Aims and Scope Contaminated land is a high priority environmental problem in most of Europe and North-America. Sweden is no exception and
generic guideline values have been developed for the initial assessment, but site-specific assessments are also needed. The
generic guideline values are not applicable when the exposure conditions are different from the typical Swedish conditions
or when the site contains a particularly sensitive ecosystem. The Swedish guideline values have, like in many other countries,
been set by using deterministic point estimates for all variables and constants in the used multimedia model. The same approach
is common also for site-specific assessments, and a limitation is that it fails to quantify variability and uncertainty. Probabilistic
risk assessment provided a method to deal with this problem. Variability and uncertainty in the input parameters (variables
or constants) are described by probability distributions, and likewise the output (risk or exposure) is presented as a probability
distribution. A substantial number of probabilistic risk assessments for contaminated land at sites in North America, Europe
and Asia have been published. However, an extensive review of the literature did not identify any study where probabilistic
risk assessment was applied to a site contaminated by an iron or steel industry. Here we will describe such a case, where
we have compared a deterministic point estimate with a probabilistic risk assessment for six elements and benzo[a]pyrene.
Methods The site had different metallurgical plants in operation for more than 100 years. Most parts of the steel mill were closed
by the mid 1980s, and today the site is used by small-sized enterprises. The soil is contaminated with metals from the previous
industrial operations. The present owner plans to develop the site and has therefore initiated extensive investigations of
soil contamination. Sixty-two soil samples collected between 1997 and 2000 provided a good coverage of the whole site, and
were analyzed for the content of different elements and polycyclic aromatic hydrocarbons (PAH). The exposure assessments were
focused on six elements with high concentrations compared to the generic guideline values; arsenic (As), lead (Pb), cadmium
(Cd), chromium (Cr), copper (Cu) and zinc (Zn). In addition, benzo[a]pyrene was included due to the high toxicity and comparatively
high concentrations. Variability and uncertainty were characterized in a Monte Carlo simulation of exposures (10 000 iterations),
and the exposures were evaluated with two land use scenarios; less sensitive use and sensitive use.
Results and Discussion The deterministic point estimates and the probabilistic estimates of the 95th percentile are in approximately the same ranges
in the scenario of less sensitive land use. It is only the exposure for arsenic that is slightly above the toxicological reference
value (TRV) in the deterministic assessment. In the probabilistic assessment, the exposure for all elements is below the TRV.
The results for sensitive land use are applicable to a scenario where the site is developed for general housing. The deterministic
point estimates and the probabilistic estimates of the 95th percentile are also here in approximately the same ranges, but
the exposure exceeds the TRV for arsenic, cadmium and lead. Drinking water, vegetables grown on site and soil ingestion are
the major exposure pathways for this scenario. In this assessment, the estimated intake distributions are applicable to a
randomly selected individual. The probability distributions used here to characterize the different soil parameters are typically
representing both variability and uncertainty, and the same is true the majority of the exposure variables. We therefore decided
not to attempt to separate variability and uncertainty at this stage, but with additional data from a more in-depth site investigation
it might be possible to achieve this.
Conclusions and Outlook To the best of our knowledge, this study is the first report on a probabilistic risk assessment on a former iron and steel
works site. The materials handled by this industry were less toxic than for many other metallurgical operations, but contaminants
may still severely limit the options for future land use. This case study shows that probabilistic exposure estimates for
a set of soil contaminants can be quite similar to deterministic point estimates. The main difference is instead to be found
in the additional information obtained with the probabilistic assessment. The sensitivity analyses show pathways and input
variables that contribute most to variations in the total intake of each contaminant, e.g. dermal contact and ingestion of
soil, vegetables and drinking water. This information can be used both in the planning of future land use and for active measures
to reduce current exposure. The probabilistic assessment also provides information on the magnitude of exposure and the margin
of safety. This information may facilitate risk communication between decision-makers and stakeholders. The presentation of
results from probabilistic risk assessments is only briefly discussed in the literature and here we see a need for research
and opportunities for enhancement. The choice of data analytical tools may then be of importance, since more complex multimedia
models are rather difficult to decipher when implemented within traditional spreadsheet software. Some of the research needs
are identified here and in a previous review article in this journal. 相似文献
63.
The temperature dependence of litter and soil organic matter (SOM) mineralisation is important because it determines how strong the feedback from the expected warmer climate may be on the atmospheric CO2 concentration. We have used a simple, analytical model to investigate how three different mechanism (i) the rate at which decomposers take up substrate at their surface; (ii) the rate by which substrate diffuses up to the surface of the decomposer; and (iii) the rate at which substrate is made available in the environment interact to determine the temperature response. The mechanisms are characterised by activation energies; two for the uptake rate (i) and one for each of the other two (ii, iii). The model shows that the temperature dependence is the result of the number of processes that effectively contributes to the rate of mineralisation; this result should also be valid if other processes are included. Depending upon the relative magnitude of the four activation energies, the temperature response is mainly determined by one or two of the mechanisms. In a transition zone, where all activation energies are similar and the number of contributing processes changes, there can be either a sharp increase or a sharp decrease in the temperature response when activation energies change. 相似文献
64.
重庆市位于长江上游生态屏障的最前沿,其水土流失对整个长江流域生态安全和三峡水利枢纽工程的安全运行有着重要影响。依据1999年重庆市水土流失遥感调查结合水土流失观测资料,评价了重庆市土壤侵蚀强度及区域分布。根据USLE方程中5N因子对土壤侵蚀敏感性影响,建立了土壤侵蚀敏感性评价指标体系,对重庆市土壤侵蚀敏感性进行评价。结合GIS技术,分析了重庆市土壤侵蚀敏感性的空间分布,探讨了土壤侵蚀的敏感性原因,并提出了有关水土保持对策。 相似文献
65.
66.
67.
Porcine corpora lutea (CL) fail to show a luteolytic response to prostaglandin-F-2α (PGF-2α) (ie, luteolytic sensitivity, or LS) until ∼day 13 of the estrous cycle. In view of the importance of protein kinase C (PRKC) in PGF-2α signal transduction, it was hypothesized that limiting levels of 1 or more PRKC isoforms may explain the lack of LS before day 13. This hypothesis was tested by examining expression of mRNA and protein, and the cellular localization patterns of the 11 PRKC isoforms throughout the porcine estrous cycle, to determine whether PRKC expression correlates with and thus may be associated with the control of the acquisition of LS in the pig. The expression patterns show that for most PRKC isoforms (ie, PRKC alpha, beta 1, beta 2, delta, epsilon, theta, iota, and zeta), mRNA was maximally expressed on day 7 or day 10 (protein kinase D1 only) of the cycle, whereas PRKCs gamma, eta, and lambda were unchanged. At the protein level, only PRKC epsilon (PRKCE) significantly changed during the estrous cycle and was elevated on day 13 (versus days 4, 7, and 15; P < 0.05). By immunofluoresence, most PRKC isoforms, including PRKCE, were localized to steroidogenic large luteal cells (LLC) and small (nonendothelial cell) luteal cell subtypes (SLC). In conclusion, since the increase in PRKCE protein expression (day 13) occurred coincidentally with the onset of LS (≥day 12), these results support a potential role for PRKCE in control of the acquisition of LS in the pig. 相似文献
68.
Nutritional management of animals during pregnancy can affect glucose and insulin dynamics in the resulting offspring through influences on fetal development. Additionally, high starch feeding in mature horses is associated with reduced insulin sensitivity and an increased risk for diseases such as obesity and laminitis. However, no study has yet evaluated the effect of feeding a high starch diet to pregnant mares on glucose and insulin dynamics in their offspring. Twenty late-gestation mares maintained on pasture were provided two-thirds of digestible energy requirements from isocaloric, isonitrogenous low starch (LS, n = 10) or high starch (HS, n = 10) feed. Their foals were assessed with an insulin-modified frequently sampled intravenous glucose tolerance test at 5, 40, 80, and 160 d of age. Baseline glucose concentrations, insulin sensitivity, and insulin-independent glucose clearance in 5-d foals were all greater than values observed in mature horses and declined towards mature values as foals reached 160 d of age. Baseline glucose concentrations were all within normal range, but higher in foals born from HS mares through 80 d of age. Insulin sensitivity was not different between dietary groups until a trend for lower insulin sensitivity in HS foals emerged at 160 d of age. These data are the first to characterize decreasing insulin sensitivity and glucose tolerance in Thoroughbred foals from 5 to 160 d of age. This study also presents the first data examining glucose and insulin dynamics in developing foals in response to maternal high starch diet. 相似文献
69.
Daniela Simon Dorina Schoenrock Ingo Nolte Wolfgang Baumgrtner Ronnie Barron Reinhard Mischke 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2009,38(4):521-528
Background: Mammary tumors are the most common neoplasms in female dogs. Malignant tumors may carry a poor prognosis and necessitate surgery. Few data are available on the value of cytologic examination as a diagnostic or prognostic tool for mammary tumors in dogs. Objectives: The objectives of this study were to determine whether cytologic findings in fine‐needle aspirate specimens of canine mammary tumors correlate with histopathologic results and whether the cytologic diagnosis is associated with postoperative outcome. Methods: In this prospective study, fine‐needle aspirate samples were obtained from 50 mammary tumors in 50 dogs. Results of cytologic and histopathologic examination were compared, using the histologic diagnosis as the reference method. Kaplan–Meier log rank analysis was used to evaluate univariate association of the cytologic diagnosis with duration of survival, local control, and metastasis‐free interval. Results: Adequate cytologic samples were obtained in 43/50 (86%) cases. The cytologic diagnosis correlated with the histologic diagnosis for benign and malignant tumors in 40/43 (93%) and 35/43 (81%) cases, respectively. Cytologic examination had a sensitivity of 88% and a specificity of 96% for the diagnosis of malignancy. The cytologic diagnosis had significant univariate association with duration of survival (P=.016), recurrence‐free interval (P=.003), and metastasis‐free interval (P=.014). Conclusions: Cytologic examination of mammary tumors in the dog has satisfactory accuracy, sensitivity, and specificity for the diagnosis of malignancy and is associated with postoperative outcome. Further studies on the diagnostic accuracy of cytology as well as multivariate analysis of its preoperative prognostic value in mammary tumors in the dog are warranted. 相似文献
70.