Are peatlands in different states with respect to their thermodynamic behaviour? A simple test of peatland energy and entropy budgets

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 (ΔR_n) 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’.     

Geochronological and isotopic records of crustal storage and assimilation in the Wolverine Creek–Conant Creek system,Heise eruptive centre,Snake River Plain

Understanding the processes of differentiation of the Yellowstone–Snake River Plain (YSRP) rhyolites is typically impeded by the apparent lack of erupted intermediate compositions as well as the complex nature of their shallow interaction with the surrounding crust responsible for their typically low O isotopic ratios. A pair of normal-δ¹⁸O rhyolitic eruptions from the Heise eruptive centre in eastern Idaho, the Wolverine Creek Tuff and the Conant Creek Tuff, represent unique magmatic products of the Yellowstone hotspot preserving abundant vestiges of the intermediate differentiation steps leading to rhyolite generation. We address both shallow and deep processes of magma generation and storage in the two units by combining high-precision ID–TIMS U–Pb zircon geochronology, trace element, O and Hf isotopic studies of zircon, and Sr isotopic analyses of individual high-Mg# pyroxenes inherited from lower- to mid-crustal differentiation stages. The zircon geochronology confirms the derivation of both tuffs from the same rhyolitic magma reservoir erupted at 5.5941 ± 0.0097 Ma, preceded by at least 92 ± 14 ky of continuous or intermittent zircon saturation approximating the length of pre-eruptive magma accumulation in the upper crust. Some low-Mg# pyroxenes enclosing zircons predate the eruption by at least 45 ± 27 ky, illustrating the co-crystallisation of major and accessory phases in the near-liquidus rhyolitic melts of the YSRP over a significant period of time. Coeval zircon crystals are isotopically heterogeneous (two populations at εHf ~?5 and ?13), requiring the assembly of isotopically distinct melt pockets directly prior to, or during, the eruption. The primitive Mg# 60–90 pyroxenes are out of isotopic equilibrium with the host rhyolitic melt (⁸⁷Sr/⁸⁶Sr_i = 0.70889), covering a range of ⁸⁷Sr/⁸⁶Sr_i = 0.70705–0.70883 corresponding to ratios typical of the most radiogenic YSRP basalts to the least radiogenic YSRP rhyolites. Together with the low εHf in zircon, the Sr isotopic ratios illustrate limited assimilation dominated by radiogenic Archean crustal source materials incorporated into variably evolved YSRP melts as they progress towards rhyolitic compositions by assimilation–fractional crystallisation.     

Distribution and Characteristics of Dinosaur Eggs in China

正China is one of the most prolific countries for dinosaur material in the world,from skeletons to footprints and eggs.At present,China has documented more than 160kinds of dinosaur,35 genera and 39 ichnospecies of dinosaur footprints,and 17 genera and 44 oospecies of dinosaur eggs.The dinosaur eggs in China are mainly distributed in Xinjiang,Inner Mongolia,Ningxia,Gansu,     

Spatial and temporal constraints on regional-scale groundwater flow in the Pampa del Tamarugal Basin,Atacama Desert,Chile

Aquifers within the Pampa del Tamarugal Basin (Atacama Desert, northern Chile) are the sole source of water for the coastal city of Iquique and the economically important mining industry. Despite this, the regional groundwater system remains poorly understood. Although it is widely accepted that aquifer recharge originates as precipitation in the Altiplano and Andean Cordillera to the east, there remains debate on whether recharge is driven primarily by near-surface groundwater flow in response to periodic flood events or by basal groundwater flux through deep-seated basin fractures. In addressing this debate, the present study quantifies spatial and temporal variability in regional-scale groundwater flow paths at 20.5°S latitude by combining a two-dimensional model of groundwater and heat flow with field observations and δ¹⁸O isotope values in surface water and groundwater. Results suggest that both previously proposed aquifer recharge mechanisms are likely influencing aquifers within the Pampa del Tamarugal Basin; however, each mechanism is operating on different spatial and temporal scales. Storm-driven flood events in the Altiplano readily transmit groundwater to the eastern Pampa del Tamarugal Basin through near-surface groundwater flow on short time scales, e.g., 10⁰–10¹ years, but these effects are likely isolated to aquifers in the eastern third of the basin. In addition, this study illustrates a physical mechanism for groundwater originating in the eastern highlands to recharge aquifers and salars in the western Pampa del Tamarugal Basin over timescales of 10⁴–10⁵ years.     

Estuarine Habitat and Demographic Factors Affect Juvenile Chinook (<Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>) Growth Variability in a Large Freshwater Tidal Estuary

Estuarine rearing has been shown to enhance within watershed biocomplexity and support growth and survival for juvenile salmon (Oncorhynchus sp.). However, less is known about how growth varies across different types of wetland habitats and what explains this variability in growth. We focused on the estuarine habitat use of Columbia River Chinook salmon (Oncorhynchus tshawytscha), which are listed under the Endangered Species Act. We employed a generalized linear model (GLM) to test three hypotheses: (1) juvenile Chinook growth was best explained by temporal factors, (2) habitat, or (3) demographic characteristics, such as stock of origin. This study examined estuarine growth rate, incorporating otolith microstructure, individual assignment to stock of origin, GIS habitat mapping, and diet composition along ~130 km of the upper Columbia River estuary. Juvenile Chinook grew on average 0.23 mm/day in the freshwater tidal estuary. When compared to other studies in the basin our growth estimates from the freshwater tidal estuary were similar to estimates in the brackish estuary, but ~4 times slower than those in the plume and upstream reservoirs. However, previous survival studies elucidated a possible tradeoff between growth and survival in the Columbia River basin. Our GLM analysis found that variation in growth was best explained by habitat and an interaction between fork length and month of capture. Juvenile Chinook salmon captured in backwater channel habitats and later in the summer (mid-summer and late summer/fall subyearlings) grew faster than salmon from other habitats and time periods. These findings present a unique example of the complexity of understanding the influences of the many processes that generate variation in growth rate for juvenile anadromous fish inhabiting estuaries.     

The Oeschinensee rock avalanche,Bernese Alps,Switzerland: a co-seismic failure 2300 years ago?

Landslide deposits dam Lake Oeschinen (Oeschinensee), located above Kandersteg, Switzerland. However, past confusion differentiating deposits of multiple landslide events has confounded efforts to quantify the volume, age, and failure dynamics of the Oeschinensee rock avalanche. Here we combine field and remote mapping, topographic reconstruction, cosmogenic surface exposure dating, and numerical runout modeling to quantify salient parameters of the event. Differences in boulder lithology and deposit morphology reveal that the landslide body damming Oeschinensee consists of debris from both an older rock avalanche, possibly Kandertal, as well as the Oeschinensee rock avalanche. We distinguish a source volume for the Oeschinensee event of 37 Mm³, resulting in an estimated deposit volume of 46 Mm³, smaller than previous estimates that included portions of the Kandertal mass. Runout modeling revealed peak and average rock avalanche velocities of 65 and 45 m/s, respectively, and support a single-event failure scenario. ³⁶Cl surface exposure dating of deposited boulders indicates a mean age for the rock avalanche of 2.3 ± 0.2 kyr. This age coincides with the timing of a paleo-seismic event identified from lacustrine sediments in Swiss lakes, suggesting an earthquake trigger. Our results help clarify the hazard and geomorphic effects of rare, large rock avalanches in alpine settings.