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Fred Worrall Ross Morrison Chris Evans Joerg Kaduk Susan Page Alex Cumming Mark Rayment Nicholas Kettridge 《水文研究》2021,35(12):e14431
Whilst all ecosystems must obey the second law of thermodynamics, these physical bounds and controls on ecosystem evolution and development are largely ignored across the ecohydrological literature. To unravel the importance of these underlying restraints on ecosystem form and function, and their power to inform our scientific understanding, we have calculated the entropy budget of a range of peat ecosystems. We hypothesize that less disturbed peatlands are ‘near equilibrium’ with respect to the second law of thermodynamics and thus respond to change by minimizing entropy production. This ‘near equilibrium’ state is best achieved by limiting evaporative losses. Alternatively, peatlands ‘far-from-equilibrium’ respond to a change in energy inputs by maximizing entropy production which is best achieved by increasing evapotranspiration. To test these alternatives this study examined the energy balance time series from seven peatlands across a disturbance gradient. We estimate the entropy budgets for each and determine how a change in net radiation (ΔRn) was transferred to a change in latent heat flux (ΔλE). The study showed that: (i) The transfer of net radiation to latent heat differed significantly between peatlands. One group transferred up to 64% of the change in net radiation to a change in latent heat flux, while the second transferred as little as 27%. (ii) Sites that transferred the most energy to latent heat flux were those that produced the greatest entropy. The study shows that an ecosystem could be ‘near equilibrium’ rather than ‘far from equilibrium’. 相似文献
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Brent D. Newman Lewis Land Fred M. Phillips Geoffrey C. Rawling 《Hydrogeology Journal》2016,24(4):753-756
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In the southwestern United States, precipitation in the high mountains is a primary source of groundwater recharge. Precipitation patterns, soil properties and vegetation largely control the rate and timing of groundwater recharge. The interactions between climate, soil and mountain vegetation thus have important implications for the groundwater supply. This study took place in the Sacramento Mountains, which is the recharge area for multiple regional aquifers in southern New Mexico. The stable isotopes of oxygen and hydrogen were used to determine whether infiltration of precipitation is homogeneously distributed in the soil or whether it is partitioned among soil-water ‘compartments’, from which trees extract water for transpiration as a function of the season. The results indicate that “immobile” or “slow” soil water, which is derived primarily from snowmelt, infiltrates soils in a relatively uniform fashion, filling small pores in the shallow soils. “Mobile” or “fast” soil water, which is mostly associated with summer thunderstorms, infiltrates very quickly through macropores and along preferential flow paths, evading evaporative loss. It was found that throughout the entire year, trees principally use immobile water derived from snowmelt mixed to differing degrees with seasonally available mobile-water sources. The replenishment of these different water pools in soils appears to depend on initial soil-water content, the manner in which the water was introduced to the soil (snowmelt versus intense thunderstorms), and the seasonal variability of the precipitation and evapotranspiration. These results have important implications for the effect of climate change on recharge mechanisms in the Sacramento Mountains. 相似文献
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No meteorites from Mercury and Venus have been conclusively identified so far. In this study, we develop an original approach based on extensive Monte Carlo simulations and diffusion models to explore the radiogenic argon (40Ar*) and helium (4He*) loss behavior and the range of 40Ar/39Ar and (U‐Th)/He age signatures expected for a range of crystals if meteorites from these planets were ever to be found. We show that we can accurately date the crystallization age of a meteorite from both Mercury and Venus using the 40Ar/39Ar technique on clinopyroxene (± orthopyroxene) and that its 40Ar/39Ar age should match the Pb‐Pb age. At the surface of Mercury, phases like albite and anorthite will exhibit a complete range of 40Ar* loss ranging from 0% to 100%, whereas merrillite and apatite will show 100% 4He* loss. By measuring the crystal size and diffusion parameters of a series of plagioclase crystals, one can inverse the 40Ar* loss value to estimate the maximum temperature experienced by a rock, and narrow down the possible pre‐ejection location of the meteorite at the surface of Mercury. At the surface of Venus, plagioclase and phosphate phases will only record the age of ejection. The (U‐Th)/He systematics of merrillite and apatite will be, respectively, moderately and strongly affected by 4He* loss during the transit of the meteorite from its host planet to Earth. Finally, meteorites from Mercury or Venus will each have their own 40Ar/39Ar and (U‐Th)/He isotopic age and 38Arc cosmic ray exposure age signatures over a series of different crystal types, allowing to unambiguously recognize a meteorite for any of these two planets using radiogenic and cosmogenic noble gases. 相似文献
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