Impact of prescribed burning on Acacia nilotica seed banks and seedlings in the Astrebla grasslands of northern Australia

Acacia nilotica is a tree of international significance both as a beneficial plant and as a species prone to thicket formation and negative impacts on savannas throughout much of its range. While fire has been identified as a useful tool for controlling negative impacts of some Acacia species in Africa, A. nilotica adult trees are apparently fire tolerant. The effects of fire on seed bank mortality, viability and germination, and on juvenile plants of this species are unknown. We undertook a study to investigate the impacts of fire on seeds and first and second year seedlings in Australian Astrebla savannas. The primary objective was to determine the effects of control burns applied during the early stages of invasion and thicket formation. Because of high rates of seedling dessication post fire in 1997, supplementary watering was undertaken until fire mortality could be measured the following year. High seed mortality occurred for seeds located either in cattle dung (100%) or on the soil surface (c. 80%). Germination of those seeds that survived was enhanced following exposure to fire. Very high fire mortality (99%) was observed among first year seedlings and moderate mortality (60%) for second year seedlings even after a low intensity burn. Negative impacts on major pasture species were minimal. The implications of these findings are discussed in relation to A. nilotica fire ecology and to the efficacy of fire as a tool for managing this species.     

Feedbacks between erosion and sediment transport in experimental bedrock channels

Natural bedrock rivers flow in self‐formed channels and form diverse erosional morphologies. The parameters that collectively define channel morphology (e.g. width, slope, bed roughness, bedrock exposure, sediment size distribution) all influence river incision rates and dynamically adjust in poorly understood ways to imposed fluid and sediment fluxes. To explore the mechanics of river incision, we conducted laboratory experiments in which the complexities of natural bedrock channels were reduced to a homogenous brittle substrate (sand and cement), a single sediment size primarily transported as bedload, a single erosion mechanism (abrasion) and sediment‐starved transport conditions. We find that patterns of erosion both create and are sensitive functions of the evolving bed topography because of feedbacks between the turbulent flow field, sediment transport and bottom roughness. Abrasion only occurs where sediment impacts the bed, and so positive feedback occurs between the sediment preferentially drawn to topographic lows by gravity and the further erosion of these lows. However, the spatial focusing of erosion results in tortuous flow paths and erosional forms (inner channels, scoops, potholes), which dissipate flow energy. This energy dissipation is a negative feedback that reduces sediment transport capacity, inhibiting further incision and ultimately leading to channel morphologies adjusted to just transport the imposed sediment load. Copyright © 2007 John Wiley & Sons, Ltd.     

Patterns of heritability of decreased EROD activity and resistance to PCB 126-induced teratogenesis in laboratory-reared offspring of killifish (Fundulus heteroclitus) from a creosote-contaminated site in the Elizabeth River,VA, USA

Killifish (Fundulus heteroclitus) from a highly contaminated site on the Elizabeth River are resistant to the acute toxicity and the cytochrome P4501A (CYP1A)-inducing activity of both the sediments from the site and chemically pure polycyclic aromatic hydrocarbons (PAHs). These effects are highly heritable for one generation, but heritable to a lesser degree by subsequent generations, in clean conditions in the laboratory. We show that offspring of this population of Elizabeth River killifish are also resistant to the teratogenicity and P4501A-inducing activity of PCB congener 126, a prototypical coplanar halogenated aromatic hydrocarbon (HAH). Furthermore, the pattern of greater resistance to acute toxicity and P4501A-inducing activity in the first generation and less in subsequent generations is also observed upon exposure to PCB-126.     

Surface evolution of dissolving minerals investigated with a kinetic Ising model

In natural weathering systems, both the chemistry and the topography of mineral surfaces change as rocks and minerals equilibrate to surface conditions. Most geochemical research has focused on changes in solution chemistry over time; however, temporal changes in surface topography may also yield information about rates and mechanisms of dissolution. We use stochastic dissolution simulations of a regular 2-D lattice with reaction mechanisms defined in terms of nearest neighbor interactions to elucidate how the surface area and reactivity of a crystal evolve during dissolution. Despite the simplicity of the model, it reproduces key features observed or inferred for mineral dissolution. Our model results indicate that: (i) dissolving surfaces reach a steady-state conformation after sufficient dissolution time, (ii) linear defects cause surface area and dissolution rate to vary in concert with one another, (iii) sigmoidal and non-sigmoidal rate vs. free-energy of reaction (ΔG_rxn) behavior can be rationalized in terms of the multiple steps occurring during dissolution, and (iv) surface roughness as a function of ΔG_rxn is highly sensitive to the reaction mechanism. When simulated times to reach steady-state are compared to published time series rate data using suitable scaling, good agreement is found for silicate minerals while the model significantly over-predicts the duration of the transient for Fe and Al oxides. The implication of our simple model is that many aspects of mineral dissolution behavior, including approach to steady-state, sigmoidal vs. non-sigmoidal rate vs. ΔG_rxn behavior, and development of rougher surfaces in conditions further from equilibrium can be explained by nearest neighbor interactions and simple Kossel-type models where reactivity of a surface is defined in terms of perfect surface, step, and kink sites.     

Sources of mercury to San Francisco Bay surface sediment as revealed by mercury stable isotopes

Mercury (Hg) concentrations and isotopic compositions were examined in shallow-water surface sediment (0-2 cm) from San Francisco (SF) Bay to determine the extent to which historic Hg mining contributes to current Hg contamination in SF Bay, and to assess the use of Hg isotopes to trace sources of contamination in estuaries. Inter-tidal and wetland sediment had total Hg (Hg_T) concentrations ranging from 161 to 1529 ng/g with no simple gradients of spatial variation. In contrast, inter-tidal and wetland sediment displayed a geographic gradient of δ²⁰²Hg values, ranging from −0.30‰ in the southern-most part of SF Bay (draining the New Almaden Hg District) to −0.99‰ in the northern-most part of SF Bay near the Sacramento-San Joaquin River Delta. Similar to SF Bay inter-tidal sediment, surface sediment from the Alviso Slough channel draining into South SF Bay had a δ²⁰²Hg value of −0.29‰, while surface sediment from the Cosumnes River and Sacramento-San Joaquin River Delta draining into north SF Bay had lower average δ²⁰²Hg values of −0.90‰ and −0.75‰, respectively. This isotopic trend suggests that Hg-contaminated sediment from the New Almaden Hg District mixes with Hg-contaminated sediment from a low δ²⁰²Hg source north of SF Bay. Tailings and thermally decomposed ore (calcine) from the New Idria Hg mine in the California Coast Range had average δ²⁰²Hg values of −0.37 and +0.03‰, respectively, showing that Hg calcination fractionates Hg isotopes resulting in Hg contamination from Hg(II) mine waste products with higher δ²⁰²Hg values than metallic Hg(0) produced from Hg mines. Thus, there is evidence for at least two distinct isotopic signals for Hg contamination in SF Bay: Hg associated with calcine waste materials at Hg mines in the Coast Range, such as New Almaden and New Idria; and Hg(0) produced from these mines and used in placer gold mines and/or in other industrial processes in the Sierra Nevada region and SF Bay area.     

Geomorphic process from topographic form: automating the interpretation of repeat survey data in river valleys

The ability to quantify the processes driving geomorphic change in river valley margins is vital to geomorphologists seeking to understand the relative role of transport mechanisms (e.g. fluvial, aeolian, and hillslope processes) in landscape dynamics. High‐resolution, repeat topographic data are becoming readily available to geomorphologists. By contrasting digital elevation models derived from repeat surveys, the transport processes driving topographic changes can be inferred, a method termed ‘mechanistic segregation.’ Unfortunately, mechanistic segregation largely relies on subjective and time consuming manual classification, which has implications both for its reproducibility and the practical scale of its application. Here we present a novel computational workflow for the mechanistic segregation of geomorphic transport processes in geospatial datasets. We apply the workflow to seven sites along the Colorado River in the Grand Canyon, where geomorphic transport is driven by a diverse suite of mechanisms. The workflow performs well when compared to field observations, with an overall predictive accuracy of 84% across 113 validation points. The approach most accurately predicts changes due to fluvial processes (100% accuracy) and aeolian processes (96%), with reduced accuracy in predictions of alluvial and colluvial processes (64% and 73%, respectively). Our workflow is designed to be applicable to a diversity of river systems and will likely provide a rapid and objective understanding of the processes driving geomorphic change at the reach and network scales. We anticipate that such an understanding will allow insight into the response of geomorphic transport processes to external forcings, such as shifts in climate, land use, or river regulation, with implications for process‐based river management and restoration. Copyright © 2017 John Wiley & Sons, Ltd.     

国际矿物学协会新矿物及矿物命名委员会（CNMMN,IMA）1998年批准的新矿物

本文的资料是国际矿物学协会新矿物及矿物命名委员会提供的,以资矿物学家在新矿物研究工作中参考和对比。ＣＮＭＭＮ鼓励其成员将本文提交其所在国家的有关刊物发表。中译文由中国新矿物及矿物命名委员会供稿。文中所列的已经批准的新矿物的名称及其详细资料,将由每个新...     

Improvement of distributed snowmelt energy balance modeling with MODIS‐based NDSI‐derived fractional snow‐covered area data

Describing the spatial variability of heterogeneous snowpacks at a watershed or mountain‐front scale is important for improvements in large‐scale snowmelt modelling. Snowmelt depletion curves, which relate fractional decreases in snow‐covered area (SCA) against normalized decreases in snow water equivalent (SWE), are a common approach to scale‐up snowmelt models. Unfortunately, the kinds of ground‐based observations that are used to develop depletion curves are expensive to gather and impractical for large areas. We describe an approach incorporating remotely sensed fractional SCA (FSCA) data with coinciding daily snowmelt SWE outputs during ablation to quantify the shape of a depletion curve. We joined melt estimates from the Utah Energy Balance Snow Accumulation and Melt Model (UEB) with FSCA data calculated from a normalized difference snow index snow algorithm using NASA's moderate resolution imaging spectroradiometer (MODIS) visible (0·545–0·565 µm) and shortwave infrared (1·628–1·652 µm) reflectance data. We tested the approach at three 500 m² study sites, one in central Idaho and the other two on the North Slope in the Alaskan arctic. The UEB‐MODIS‐derived depletion curves were evaluated against depletion curves derived from ground‐based snow surveys. Comparisons showed strong agreement between the independent estimates. Copyright © 2010 John Wiley & Sons, Ltd.     

Ultraviolet light curves of V535 Arae

Observations of V535 Ara obtained with IUE define the light curve of this long-period W UMa binary in the ultraviolet and let us estimate its gravity darkening. This star was chosen as a contact binary near the high-T _eff limit for convection. The ultraviolet colours and spectral type correspond to (B–V)₀=0.24, or A8V, and imply the star should have very little residual convection in its envelope. The gravity darkening thus ought to be large, as in a radiative star, unless it is modified by circulation in the common envelope, or unless all stars this warm are convective. The light-curve analysis is complicated by a long-term wave that depresses the orbital phases before and after secondary eclipse. We have obtained four solutions to a combination of optical and ultraviolet light curves, two for high, radiative gravity darkening and two for low, convective gravity darkening. For each value of the gravity-darkening exponent, we let the larger, more massive binary component either (a) have a dark spot in its back side or (b) have an excessively hot side facing its companion. The light curves were fitted equally well in all four cases; however, in all but the one with low-gravity darkening and a hot inner face there was a rather large global temperature difference between the two stars. The primary component of this system appears to be significantly undermassive for its spectral type, more so than the primary in AW UMa, but this probably results simply from systematic errors in a radial-velocity solution by Schöffel. It is suggested that the W UMa binaries are found only at spectral types later than about A8 because their outer envelopes must be convective to transfer luminosity.