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241.
Veiko Uri Krista LõhmusÜlo Mander Ivika OstonenJürgen Aosaar Martin MaddisonHeljä-Sisko Helmisaari Jürgen Augustin 《Ecological Engineering》2011,37(6):920-930
Short-rotation energy forestry is one of the potential ways for management of abandoned agricultural areas. It helps sequestrate carbon and mitigate human-induced climate changes. Owing to symbiotic dinitrogen (N2) fixation by actinomycetes and the soil fertilizing capacity and fast biomass growth of grey alders, the latter can be suitable species for short-rotation forestry. In our study of a young grey alder stand (Alnus incana (L.) Moench) on abandoned arable land in Estonia we tested the following hypotheses: (1) afforestation of abandoned agricultural land by grey alder significantly affects the soil nitrogen (N) status already during the first rotation period; (2) input of symbiotic fixation covers an essential part of the plant annual N demand of the stand; (3) despite a considerable N input into the ecosystem of a young alder stand, there will occur no significant environmental hazards (N leaching or N2O emissions). The first two hypotheses can be accepted: there was a significant increase in N and C content in the topsoil (from 0.11 to 0.14%, and from 1.4 to 1.7%, respectively), and N fixation (151.5 kg N ha−1 yr−1) covered about 74% of the annual N demand of the stand. The third hypothesis met support as well: N2O emissions (0.5 kg N ha−1 yr−1) were low, while most of the annual gaseous N losses were in the form of N2 (73.8 kg N ha−1 yr−1). Annual average NO3-N leaching was 15 kg N ha−1 yr−1 but the N that leached from topsoil accumulated in deeper soil layers. The soil acidifying effect of alders was clearly evident; during the 14-year period soil acidity increased 1.3 units in the upper 0-10 cm topsoil layer. 相似文献
242.
Kaido SoosaarÜlo Mander Martin MaddisonArno Kanal Ain KullKrista Lõhmus Jaak TruuJürgen Augustin 《Ecological Engineering》2011,37(1):40-53
We studied greenhouse gas (GHG) fluxes in two differently loaded riparian Alnus incana-dominated forests in agricultural landscapes of southern Estonia: a 33-year-old stand in Porijõgi, in which the uphill agricultural activities had been abandoned since the middle of the 1990s, and a 50-year-old stand in Viiratsi, which still receives polluted lateral flow from uphill fields fertilized with pig slurry. In Porijõgi, closed-chamber based sampling lasted from October 2001 to October 2009, whereas in Viiratsi the sampling period was from November 2003 to October 2009. Both temporal and spatial variations in all GHG gas fluxes were remarkable. Local differences in GHG fluxes between micro-sites (“Edge”, “Dry” and “Wet” in Porijõgi, and “Wet”, “Slope” and “Dry” in Viiratsi) were sometimes greater than those between sites. Median values of GHG fluxes from both sites over the whole study period and all microsites did not differ significantly, being 45 and 42 mg CO2-C m−2 h−1, 8 and 0.5 μg CH4-C m−2 h−1, 1.0 and 2.1 mg N2-N m−2 h−1, and 5 and 9 μg N2O-N m−2 h−1, in Porijõgi and Viiratsi, respectively. The N2:N2O ratio in Viiratsi (40-1200) was lower than in Porijõgi (10-7600). The median values-based estimation of the Global Warming Potential of CH4 and N2O was 19 and 185 kg CO2 equivalents (eq) ha−1 yr−1 in Porijõgi and −14 and 336 kg CO2 eq ha−1 yr−1 in Viiratsi, respectively. A significant Spearman rank correlation was found between the mean monthly air temperature and CO2, CH4 and N2 fluxes in Porijõgi, and N2O flux in Viiratsi, and between the monthly precipitation and CH4 fluxes in both study sites. Higher groundwater level significantly increases CH4 emission and decreases CO2 and N2O emission, whereas higher soil temperature significantly increases N2O, CH4 and N2 emission values. In Porijõgi, GHG emissions did not display any discernable trend, whereas in Viiratsi a significant increase in CO2, N2, and N2O emissions has been found. This may be a result of the age of the grey alder stand, but may also be caused by the long-term nutrient load of this riparian alder stand, which indicates a need for the management of similar heavily loaded riparian alder stands. 相似文献
243.
The performance of acetic acid-supported pH-heterogenized heterotrophic denitrification (HD) facilitated with ferrous sulfide-based autotrophic denitrification (AD) was investigated in upflow activated carbon-packed column reactors for reliable removal of highly elevated nitrate (42 mg NO3-N l−1) in drinking water. The use of acetic acid as substrate provided sufficient internal carbon dioxide to completely eliminate the need of external pH adjustment for HD, but simultaneously created vertically heterogenized pH varying from 4.8 to 7.8 in the HD reactor. After 5-week acclimation, the HD reactor developed a moderate nitrate removal capacity with about one third of nitrate removal occurring in the acidic zone (pH 4.8–6.2). To increase the treatment reliability, acetic acid-supported HD was operated under 10% carbon limitation to remove >85% of nitrate, and ferrous sulfide-based AD was supplementally operated to remove residual nitrate and formed nitrite without excess of soluble organic carbon, nitrite or sulfate in the final effluent. 相似文献
244.
F.J. Álvarez-HornosD. Volckaert P.M. HeynderickxH. Van Langenhove 《Bioresource technology》2011,102(19):8893-8898
Ethyl acetate removal from an air stream was carried out by using a flat composite membrane bioreactor. The composite membrane consisted of a dense polydimethylsiloxane top layer with an average thickness of 0.3 μm supported in a porous polyacrylonitrile layer (50 μm). The membrane bioreactor (MBR) was operated during 3 months, and a maximum elimination capacity of 225 g m−3 h−1 at an empty bed residence time of 60 s was observed. Removal efficiencies higher than 95% were obtained for inlet loads lower than 200 g m−3 h−1 and empty bed residence times as short as 15 s. The estimated yield coefficient, determined from the carbon dioxide production, resulted in 0.82 g dry biomass synthesized per gram of ethyl acetate degraded. No data of ethyl acetate treatment in MBR have been found in the literature, but the results illustrate that membrane bioreactors can potentially be a good option for its treatment. 相似文献
245.
This work examined the energy return of Chlorella vulgaris and Dunaliella tertiolecta cultivated in a gas-sparged photobioreactor design where the power input for sparging was manipulated (10, 20, and 50 W m−3). Dry weight, organic carbon and heating values of the biomass were measured, plus a suite of variables including Fv/Fm and dissolved oxygen. A model for predicting the higher heating value of microalgal biomass was developed and used to measure the energetic performance of batch cultivations. High power inputs enhanced maximum biomass yields, but did not improve the energy return. Cultivation in 10 W m−3 showed up to a 39% higher cumulative net energy return than 50 W m−3, and increased the cumulative net energy ratio up to fourfold. The highest net energy ratio for power input was 19.3 (D. tertiolecta, 12% CO2, 10 W m−3). These systems may be a sustainable method of biomass production, but their effectiveness is sensitive to operational parameters. 相似文献
246.
Until the end of last century, scientists began to show their concern about greenhouse gas emission from reservoirs and questioned the “green credential” of hydroelectric dams since then. Through measurements along the channel of the TGR, an unexpectedly low CH4 emission rate was recently observed from the surface of the TGR, much lower than our assumed estimate before. Moreover, the rate from the TGR is lower than that from many hydroelectric reservoirs. One possible reason for such a low emission rate is that lack of substrates supplied by decomposed vegetation limits the CH4 production in the sediment of the TGR because of vegetation clearance since 2002 before impounding, whose primary purpose is to conserve the water quality. These results indicated that TGR is not a hotspot of CH4 emission. On a broader sense, it also indicated that removal of flooded vegetation would help to decrease CH4 emission from dam reservoirs before impounding, especially in the drawdown area. 相似文献
247.
In an island population receiving immigrants from a larger continental population, gene flow causes maladaptation, decreasing mean fitness and producing continued directional selection to restore the local mean phenotype to its optimum. We show that this causes higher plasticity to evolve on the island than on the continent at migration-selection equilibrium, assuming genetic variation of reaction norms is such that phenotypic variance is higher on the island, where phenotypes are not canalized. For a species distributed continuously in space along an environmental gradient, higher plasticity evolves at the edges of the geographic range, and in environments where phenotypes are not canalized. Constant or evolving partially adaptive plasticity also alleviates maladaptation owing to gene flow in a heterogeneous environment and produces higher mean fitness and larger population size in marginal populations, preventing them from becoming sinks and facilitating invasion of new habitats. Our results shed light on the widely observed involvement of partially adaptive plasticity in phenotypic clines, and on the mechanisms causing geographic variation in plasticity. 相似文献
248.
Research in the soil of the tropics mostly has demonstrated the decline of soil organic carbon (SOC) after conversion of primary forest to plantation and cultivated lands. This paper illustrates the dynamics of SOC on the island of Java, Indonesia, from 1930 to 2010. We used 2002 soil profile observations containing organic carbon (C) analysis in the topsoil, which were collected by the Indonesian Center for Agricultural Land Resources Research & Development from 1923 to 2007. Results show the obvious decline of SOC values from around 2% in 1930–1940 to 0.8% in 1960–1970. However, there has been an increase of SOC content since 1970, with a median level of 1.1% in the year 2000. Our analysis suggests that the human influence and agricultural practices on SOC in Java have been a stronger influence than the environmental factors. SOC for the top 10 cm has shown a net accumulation rate of 0.2–0.3 Mg C ha?1 yr?1 during the period 1990–2000. These findings give rise to optimism for increased soil C sequestration in the tropics. 相似文献
249.
Sigrid Dengel Peter E. Levy John Grace Stephanie K. Jones Ute M. Skiba 《Global Change Biology》2011,17(12):3524-3533
Methane (CH4) is an important greenhouse gas, contributing 0.4–0.5 W m?2 to global warming. Methane emissions originate from several sources, including wetlands, rice paddies, termites and ruminating animals. Previous measurements of methane flux from farm animals have been carried out on animals in unnatural conditions, in laboratory chambers or fitted with cumbersome masks. This study introduces eddy covariance measurements of CH4, using the newly developed LI‐COR LI‐7700 open‐path methane analyser, to measure field‐scale fluxes from sheep grazing freely on pasture. Under summer conditions, fluxes of methane in the morning averaged 30 nmol m?2 s?1, whereas those in the afternoon were above 100 nmol m?2 s?1, and were roughly two orders of magnitude larger than the small methane emissions from the soil. Methane emissions showed no clear relationship with air temperature or photosynthetically active radiation, but some diurnal pattern was apparent, probably linked to sheep grazing behaviour and metabolism. Over the measurement period (days 60–277, year 2010), cumulative methane fluxes were 0.34 mol CH4 m?2, equating to 134.3 g CO2 equivalents m?2. By comparison, a carbon dioxide (CO2) sink of 819 g CO2 equivalents m?2 was measured over the same period, but it is likely that much of this would be released back to the atmosphere during the winter or as off‐site losses (through microbial and animal respiration). By dividing methane fluxes by the number of sheep in the field each day, we calculated CH4 emissions per head of livestock as 7.4 kg CH4 sheep?1 yr?1, close to the published IPCC emission factor of 8 kg CH4 sheep?1 yr?1. 相似文献
250.