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A.-K. Viitanen T. Mattila J.M. Mkel M. Marjamki O. Anttalainen J. Keskinen 《Atmospheric Research》2008,90(2-4):115-ICNAA07
Ion mobility spectrometry offers a robust and effective technique to study ion clusters in ambient conditions. Here, we have experimentally studied the influence of temperature on the positive ion cluster formation of 2-propanol vapor in air, along with parallel measurements for n-butyl acetate vapor in air. For both of these low proton affinity compounds in the ppm concentration range, temperatures below 0 °C tend to favor formation of dimers and trimers. The measurements indicate that approximate estimations for the fractions of these n-mers (n > 1) in the ion spectra, can be obtained by classical theory for ion induced nucleation. Presence of natural background vapors however slightly blurs the data, especially for the fraction of monomers, so that accurate prediction of the fractions of n-mers in the spectra would require more accurate information on the gas composition. The findings concerning thermal behavior of ions help to understand better ion phenomena also in field conditions. 相似文献
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ABSTRACTWe greatly enjoyed reading the paper by Liu et al., which is both timely and rich in insight, as it discusses the challenges in operationalizing the water–energy–food security (WEF) nexus. The nexus approach is gaining increasing attention, both in research and in policy documents, as reflected in the number and content of published documents in the past years and highlighted by the authors. 相似文献
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Numerous rootless fumaroles were developed on pyroclastic flows and a lava flow generated during the March 1986 eruptive cycle of Mount St. Augustine. Gases issued from fumarole vents with four different shapes: fissure, phreatic explosion crater, single/multiple ovoid opening, and diffuse, multiple opening. Fumarole distribution and morphology were controlled by preeruption drainage and topography, as well as by the thickness, compaction, and settling of the flow deposits. Fumarole temperatures measured in June and July 1986 ranged from 75°–394°C. Varying amounts of colorful and often roughly zoned encrustations are associated with all fumarole vent shapes. Only six types of crystalline phases were detected by X-ray diffraction, with gypsum the most abundant mineral, followed by anhydrite, sulfur, tridymite, halite, and soda alum. Scanning electron microscopy and energy dispersive X-ray analysis revealed a number of amorphous phases, mainly halogen-rich, as well as other minor crystalline phases. The mineral assemblages in the encrustations suggest formation conditions for these deposits within a general range of 25°–250°C in an oxidizing environment. Many of the amorphous phases are metastable and upon cooling of the fumarole lose nonstructural water and crystallize to more stable forms. The high halogen contents of the fumarole condensates and the mineralogy, chemistry, and morphology of the encrustations support leaching of the andesitic ash and lava flow by condensed acid vapors as the primary source for the chemical components contained in the encrustations. Comparison of traceelement (Sr, Ba, V, Co, Ni, and Cr) contents in unaltered and altered ash suggests that trace-element distribution follows a pattern of isomorphic substitution in the encrustation phases. 相似文献
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ABSTRACTWe greatly enjoyed reading the paper by Liu et al., which is both timely and rich in insight, as it discusses the challenges in operationalizing the water–energy–food security (WEF) nexus. The nexus approach is gaining increasing attention, both in research and in policy documents, as reflected in the number and content of published documents in the past years and highlighted by the authors. 相似文献
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Reclamation of peat bogs for agriculture changes the physical and chemical characteristics of the peat matrix, for example, drainage and tillage accelerate decomposition, altering peat porosity, pore size distribution, and hydraulic properties. This study investigated changes in near-saturated hydraulic conductivity over time after drainage of peat soil for agricultural use by conducting tension infiltrometer measurements in a mire that has been gradually drained and reclaimed for agriculture during the past 80 years (with fields drained 2, 12, 40, and 80 years before the measurements). At pore water pressure closest to saturation (pressure head −1 cm), hydraulic conductivity in the newest field was approximately nine times larger than that in the oldest field, and a decreasing trend with field age was observed. A similar (but weaker) trend was observed with −3 cm pressure head (approximately four times larger in the newest field in comparison to the oldest), but at −6 cm head, there were no significant differences. These results indicate that peat degradation reduces the amount of millimetre-sized pores in particular. They also indicate that changes in peat macroporosity continue for several decades before a new steady state is reached. 相似文献
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Jari Syväranta Pia Högmander Tapio Keskinen Juha Karjalainen Roger I. Jones 《Aquatic Sciences - Research Across Boundaries》2011,73(1):79-89
We used carbon and nitrogen stable isotope analyses to assess the relative contributions from pelagic and littoral energy sources to higher trophic levels in a lake ecosystem before and after a major food web perturbation. The food web structure of the lake was altered when the population sizes of the most abundant fish species (small perch, roach and bream) were reduced during an attempt to improve water quality by biomanipulation. Fish removal was followed by dense year classes of young fish, which subsequently increased the utilisation of pelagic resources. This was reflected as a decrease in relative energy contribution from littoral sources and also led to more distinct pelagic and littoral food chains after fish removal. Community metrics calculated from stable isotope data indicated increased trophic diversity and occupied niche area, and reduced trophic redundancy in the food web. However, only minor changes were observed in fish trophic positions, although roach and pike occupied slightly lower trophic positions after fish removal. Despite the Jyväsjärvi ecosystem becoming more dependent on pelagic energy after fish removals, the littoral energy contribution was still substantial, particularly to certain fish species. Hence, our results support recent arguments for the importance of benthic production in lake ecosystems. More generally, our results illustrate how large-scale perturbations of food web structure can alter energy flow patterns through an entire ecosystem. 相似文献
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Laukka Vuokko Katko Tapio S. Peltonen Lasse Rajala Riikka 《Hydrogeology Journal》2021,29(4):1369-1378
In Finland, community water supply has increasingly relied on natural groundwater and artificially recharged groundwater as the raw water source. Several managed aquifer recharge (MAR) projects have been co-created with involved parties and have proceeded well, while some cases have raised considerable resistance among the stakeholders. It seems that success or failure in MAR cooperation is related to management cultures and the ways in which various interests are taken into account, from the very beginning and throughout the process. Empirically, this paper builds on comparison between two conflictual case studies in Finland: one in the Tampere region and the other in the Turku region. The study analyses the major constraints of these projects through the lens of collaborative rationality, also drawing upon discourse analysis and negotiation theory. The material is gathered through thematic interviews of stakeholders, newspaper articles and a stakeholder workshop. The results indicate that conventional management approaches, drawing from expert-based instrumental rationality, were insufficient in both cases. The collaborative rationality framework suggests that legitimacy for the groundwater projects should be gained through joint knowledge production and inclusive multiparty interaction for creating options for collaboration. Both cases lacked the tools and know-how for authentic dialogue and collaboration. The emerging paradigm emphasizes more collaborative approaches for natural resources management and urban planning. While MAR projects operate inside these areas and are highly complex in nature, it is essential to embrace the emerging paradigm in order to promote MAR systems along with their huge potential.
相似文献8.
Ari Venäläinen Heikki Tuomenvirta Riikka Lahtinen Martti Heikinheimo 《Climatic change》2001,50(1-2):111-128
The influence of the predicted climate warming on soil frost conditions in Finland was studied using a climate scenario based on a Hadley Centre (U.K.) global ocean-atmosphere general circulation model (HadCM2) run. HadCM2 results were dynamically downscaled to the regional level using the regional climate model at the Rossby Centre (Sweden). The future period this study focuses on is the end of the 21st century. The study was limited to ground surface conditions in which snow has been removed. The predicted air temperature rise was interpreted in terms of changes in soil frost conditions using an empirical dependence that was found between measured soil frost depths and the sum of daily mean air temperatures calculated from the beginning of the freezing period. On average the annual maximum soil frost depth will decrease in southern and central Finland from the present approx. 100–150 cm by about 50 cm. In northern Finland the change will be from depths of about 200–300 cm to about 100–200 cm depending on station. The annual maximum soil frost depth in the future would thus be about the same in northern Finland as it is in the current climate in southern Finland. In southern Finland after about 100 years the ground will seldom be frozen in December and even in January there will be no soil frost in about half of the years. In Central and northern Finland the probability of completely unfrozen ground in December–March is very small, even in the future. 相似文献
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Two widespread tephra deposits constrain the age of the Delta Glaciation in central Alaska. The Old Crow tephra (ca. 140,000 ± 10,000 yr), identified by electron microprobe and ion microprobe analyses of individual glass shards, overlies an outwash terrace coeval with the Delta glaciation. The Sheep Creek tephra (ca. 190,000 yr) is reworked in alluvium of Delta age. The upper and lower limiting tephra dates indicate that the Delta glaciation occurred during marine oxygen isotope stage 6. We hypothesize that glaciers in the Delta River Valley reached their maximum Pleistocene extent during this cold interval because of significant mid-Pleistocene tectonic uplift of the east-central Alaska Range. 相似文献
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