Treesearch

Increasing temperatures in northern high latitudes are causing permafrost to thaw1, making large amounts of previously frozen organic matter vulnerable to microbial decomposition2. Permafrost thaw also creates a fragmented landscape of drier and wetter soil conditions3,4 that determine the amount and form (carbon dioxide (CO2), or methane (CH4)) of carbon (C) released to the atmosphere. The rate and form of C release control the magnitude of the permafrost C feedback, so their relative contribution with a warming climate remains unclear5,6. We quantified the eect of increasing temperature...

Many microbes responsible for inorganic nutrient uptake and transformation utilize dissolved organic matter (DOM) as a nutrient or energy source, but little is known about whether DOM composition is an important driver of nutrient uptake in streams. Our goal was to determine whether incorporating DOM composition metrics with other more commonly considered biological, physical, and chemical variables improved our ability to explain patterns of ammonium (NH+4 –N) and soluble reactive phosphorus (SRP) uptake across 11 Lake Superior tributaries. Nutrient uptake velocities (Vf) ranged from...

The 2013 Rim Fire was the third largest wildfire in California history and burned 257 314 acres in the Sierra Nevada Mountains. We evaluated air-quality impacts of PM2.5from smoke from the Rim Fire on receptor areas in California and Nevada. We employed two approaches to examine the air-quality impacts: (1) an evaluation of PM2.5concentration data collected by temporary and permanent air-monitoring sites and (2) an estimation of intake fraction (iF) of PM2.5from smoke. The Rim Fire impacted locations in the central Sierra nearest to the fire and extended to the northern Sierra Nevada...

Peat can develop in any wetland area where plant production exceeds decomposition. Peatlands are most prevalent in fl at landscapes at high latitudes (tundra, boreal zones) where coo l temperatures, low evaporation rates, water-logging, and low pH combine to retard plant decomposition (Vitt 1994 ; Rochefort et al. 2012 ). Although much less expansive, peatlands can also occur under other climatic conditions provided decomposition is still slow (see the below section on the Okefenokee Swamp). Peatlands are often classifi ed as either bogs or fens, with bogs receiving nutrients almost...

Aim: Ecological niche theory states that realized niche breadth should increase with population growth. This relationship has been studied extensively in the context of density-dependent habitat selection, and there is evidence that animal populations at higher density occupy a wider range of vegetation types. To our knowledge, no previous studies have investigated the relationship between population growth and climate niche breadth (i.e. the range of climatic conditions occupied). Here we aim to estimate the influence of population trend, as well as changes in distribution, on realized...

We used radiotelemetry and observations of color-banded birds in Costa Rica and Nicaragua to characterize the social system and foraging behavior of Golden-winged Warblers (Vermivora chrysoptera) at the nonbreeding grounds, and we assessed how these behaviors affected intraspecific spacing and home-range size. Golden-winged Warblers spent the majority of their time associating with mixed-species flocks composed of migrant and resident species. Males were territorial, responding aggressively to broadcast vocalizations and exhibiting a high degree of within- and among-season site fidelity....

Simulating an advancing fire front may be achieved within a Lagrangian or Eulerian framework. In the former, independently moving markers are connected to form a fire front, whereas in the latter, values representing the moving front are calculated at points within a fixed grid. Despite a mathematical equivalence between the two methods, it is not clear that both will produce the same results when implemented numerically. Here, we describe simulations of fire spread created using a level set Eulerian approach (as implemented in the wildland-urban interface fire dynamics simulator, WFDS)...

Pinus yunnanensis is the main species used for reforestation in Yunnan province, China. To manage the genetic resources of this economically and ecologically important species efficiently, greater knowledge of the distribution of its genetic diversity is needed. In this study, the genetic diversity of 20 natural populations representing most of the P. yunnanensis range was examined using seven simple sequence repeats. No loci showed significant departure from Hardy-Weinberg equilibrium. Most genetic diversity was found within populations, and overall genetic differentiation was low (FST =...

This paper presents recent progress in the development of seismic performance factors for cross-laminated timber (CLT) systems in the United States. A brief overview of some of other systematic studies conducted in Europe, North America, and Japan is also provided. The FEMA P695 methodology is briefly described and selected results from connector testing and CLT wall testing are discussed. Shear and uplift tests were performed on generic angle brackets to quantify their behavior. CLT walls with these connectors were then tested investigate the influence of various parameters on wall...

The formation of graphene-encapsulated copper nanoparticles was investigated through carbonizing a mixture of kraft lignin and copper sulfate pentahydrate at the temperature up to 500 °C. The abrupt conversion of copper ions into its atoms occurred at 300 °C. The formation of graphene layers surrounding copper nanoparticles started as early as the heating temperature reached 400 °C. Most copper nanoparticles were covered with less than five graphene layers when the temperature reached 500 °C. The average diameter of graphene-encapsulated copper nanoparticles was 12.75 and 11.62 nm for...