David Nelson

University of Maryland Center for Environmental Science | UMCES · Appalachian Laboratory

Water quality impacts of stream water nitrate (NO3-) on downstream ecosystems are largely determined by the load of NO3- from the watershed to surface waters. The largest NO3- loads often occur during storm events, but it is unclear how loads of different NO3- sources change during storm events relative to baseflow or how watershed attributes might...

Abstract The expansion of industrial‐scale wind‐energy facilities has not only increased the production of low‐carbon emission energy but has also resulted in mortality of wildlife, including migratory bats. Management decisions can be limited by a lack of understanding of the geographic impact of bats killed at wind‐energy facilities. Several stud...

Plant megafossils from the Paleocene-Eocene Thermal Maximum (PETM) in the Bighorn Basin, north-central Wyoming, USA, document a dramatic shift in floral composition, whereas palynofloral change from the same sections has appeared to be more subtle. We investigated this discrepancy by quantifying pollen preservation and measuring the stable carbon i...

Alder (Alnus spp.) and Pacific salmon (Oncorhynchus spp.) provide key nutrient subsidies to freshwater systems. In southwestern Alaska, alder-derived nutrients (ADNs) are increasing as alder cover expands in response to climate warming, while climate change and habitat degradation are reducing marine-derived nutrients (MDNs) in salmon-spawning habi...

White-nose syndrome (WNS) is an emerging fungal epizootic disease that has caused large-scale mortality in several species of North American bats. The fungus that causes WNS, Pseudogymnoascus destructans (Pd), has also been detected in bat species without diagnostic signs of WNS. Although these species could play a role in WNS spread, understanding...

Renewable energy production can kill individual birds, but little is known about how it affects avian populations. We assessed the vulnerability of populations for 23 priority bird species killed at wind and solar facilities in California, USA. Bayesian hierarchical models suggested that 48% of these species were vulnerable to population-level effe...

Shifting range limits are predicted for many species as the climate warms. However, the rapid pace of climate change will challenge the natural dispersal capacity of long-lived, sessile organisms such as forest trees. Adaptive responses of populations will, therefore, depend on levels of genetic variation and plasticity for climate-responsive trait...

Atmospheric nitrate (NO3⁻Atm) deposition has increased dramatically during the past ~ 150 years and contributes to ecosystem eutrophication. NO3⁻Atm deposition is widespread, but the role of different landscapes in modulating watershed-scale processing and export of NO3⁻Atm remains unclear. We measured triple oxygen isotopes (a tracer of NO3⁻Atm) o...

Organisms are constantly challenged by pathogens and pests which can drive the evolution of growth‐defense strategies. Plant stomata are essential for gas‐exchange during photosynthesis and conceptually lie at the intersection of the physiological demands of growth and exposure to foliar fungal pathogens. Generations of natural selection for locall...

The geographic distributions of eastern and western Lasionycteris noctivagans populations suggest they could be genetically isolated, but this has rarely been assessed using genetic data. Here, we evaluate this possibility by sequencing the complete mitochondrial genome of four silver-haired bats from eastern and western populations. The three usab...

The expansion of the wind energy industry has had benefits in terms of increased renewable energy production but has also led to increased mortality of migratory bats due to interactions with wind turbines. A key question that could guide bat-related management activities is identifying the geographic origin of bats killed at wind-energy facilities...

Understanding the factors influencing the current distribution of genetic diversity across a species range is one of the main questions of evolutionary biology, especially given the increasing threat to biodiversity posed by climate change. Historical demographic processes such as population expansion or bottlenecks and decline are known to exert a...

Fire frequency exerts a fundamental control on productivity and nutrient cycling in savanna ecosystems. Individual fires often increase short-term nitrogen (N) availability to plants, but repeated burning causes ecosystem N losses and can ultimately decrease soil organic matter and N availability. However, these effects remain poorly understood due...

Probability-of-origin maps deduced from stable isotope data are important for inferring broad-scale patterns of animal migration, but few resources and tools for interpreting and validating these maps exist. For example, quantitative tools for comparing multiple probability-of-origin maps do not exist, and many existing approaches for geographic as...

Abstract. Fire frequency exerts a fundamental control on productivity and nutrient cycling in savanna ecosystems. A single fire event often increases short-term nitrogen (N) availability to individual plants, but repeated burning causes ecosystem carbon and N losses and can ultimately decrease soil organic matter and N availability. However, these...

Human activity influences wildlife. However, the ecological and conservation significances of these influences are difficult to predict and depend on their population-level consequences. This difficulty arises partly because of information gaps, and partly because the data on stressors are usually collected in a count-based manner (e.g., number of...

A limitation to understanding drivers of long-term trends in terrestrial nitrogen (N) availability in forests and its subsequent influence on stream nitrate export is a general lack of integrated analyses using long-term data on terrestrial and aquatic N cycling at comparable spatial scales. Here we analyze relationships between stream nitrate conc...

1.Fire activity is changing dramatically across the globe, with uncertain effects on ecosystem processes, especially belowground. Fire‐driven losses of soil carbon (C) are often assumed to occur primarily in the upper soil layers because the repeated combustion of aboveground biomass limits organic matter inputs into surface soil. However, C losses...

Little is known about the regional extent and variability of nitrate from atmospheric deposition that is transported to streams without biological processing in forests. We measured water chemistry and isotopic tracers of nitrate sources across the Northern Forest Region of the USA and Canada and reanalyzed data from other studies to determine when...

The temporal dynamics of soil bacterial communities are understudied, but such understanding is critical to elucidating the drivers of community variation. The goal of this study was to characterize how soil bacterial communities vary across diurnal, sub-seasonal and seasonal time-scales in a 5.8 m2 plot and test the hypothesis that bacterial diver...

This data publication includes water chemistry, nitrate isotopic values (δ15N and δ18O), apportioned amounts of unprocessed atmospheric nitrate in freshwaters, streamflow, streamflow apportioned into quick flow, and associated metadata. Data were collected from forested or predominantly forested catchments in the United States and Canada. Some samp...

Accounting for migration and connectivity of mobile species across the annual cycle can present challenges for conservation and management efforts. The use of stable isotope approaches to examine the movements and ecology of wildlife has been widespread over the past two decades. Hydrogen stable isotope (δ 2 H) composition, in particular, has been...

Human societies depend on an Earth system that operates within a constrained range of nutrient availability, yet the recent trajectory of terrestrial nitrogen (N) availability is uncertain. Examining patterns of foliar N concentrations and isotope ratios (δ15N) from more than 43,000 samples acquired over 37 years, here we show that foliar N concent...

Paleoecological records suggest that growing season length and/or cloudiness may affect peatland carbon accumulation and testate amoeba-based environmental reconstructions, highlighting a need to understand how light intensity affects microbial communities. We shaded plots on two peatlands for two years to examine effects on testate amoeba communit...

Rationale: Stable hydrogen isotope (δ2 H) ratios of animal tissues are useful for assessing movement and geographic origin of mobile organisms. However, it is uncertain whether heat and singeing affects feather δ2 H values and thus subsequent geographic assignments. This is relevant for birds of conservation interest that are burned and killed at...

Carcasses provide an important resource for assessing the vulnerability of bat species and sexes to threats, but the reliability of sex data derived from the external morphology (sexmorph) of bat carcasses remains uncertain. We used genetic‐based assessment of sex (sexgen) to evaluate the effect of carcass age and searcher identity on sexmorph‐base...

Declining near-infrared (NIR) surface reflectance between early and late summer, here termed greendown, is a common, yet poorly understood phenomena in remote sensing time series of temperate deciduous forests. As revealed by phenology analysis of Landsat satellite data, there are strong spatial patterns in the rate of greendown across temperate de...

Atmospheric nitrate deposition resulting from anthropogenic activities negatively affects human and environmental health. Identifying deposited nitrate that is produced locally vs. that originating from long-distance transport would help inform efforts to mitigate such impacts. However, distinguishing the relative transport distances of atmospheric...

Variation across climate gradients in the isotopic composition of nitrogen (N) and carbon (C) in foliar tissues has the potential to reveal ecological processes related to N and water availability. However, it has been a challenge to separate spatial patterns related to direct effects of climate from effects that manifest indirectly through species...

Forests cover 30% of the terrestrial Earth surface and are a major component of the global carbon (C) cycle. Humans have doubled the amount of global reactive nitrogen (N), increasing deposition of N onto forests worldwide. However, other global changes—especially climate change and elevated atmospheric carbon dioxide concentrations—are increasing...

Bats perform important ecosystem services, but it remains difficult to quantify their dietary strategies and trophic position (TP) in situ. We conducted measurements of nitrogen isotopes of individual amino acids (δ¹⁵NAA) and bulk-tissue carbon (δ¹³Cbulk) and nitrogen (δ¹⁵Nbulk) isotopes for nine bat species from different feeding guilds (nectarivo...

Rationale: Carbon isotope (δ(13) C values) data from arthropod cuticles provide invaluable information on past and present biogeochemical processes. However, such analyses typically require large sample sizes that may mask important variation in δ(13) C values within or among species. Methods: We have evaluated a spooling-wire microcombustion (S...

Renewable energy production is expanding rapidly despite mostly unknown environmental effects on wildlife and habitats. We used genetic and stable isotope data collected from Golden Eagles (Aquila chrysaetos) killed at the Altamont Pass Wind Resource Area (APWRA) in California in demographic models to test hypotheses about the geographic extent and...

There is wide agreement that anthropogenic climate warming has influenced the phenology of forests during the late twentieth and early twenty-first centuries1,2. Longer growing seasons can lead to increased photosynthesis and productivity3, which would represent a negative feedback to rising CO2 and consequently warming4,5. Alternatively, increased...

Recent reports suggest that decreases in atmospheric nitrogen (N) deposition throughout Europe and North America may have resulted in declining nitrate export in surface waters in recent decades, yet it is unknown if and how terrestrial N cycling was affected. During a period of decreased atmospheric N deposition, we assessed changes in forest N cy...

An unanticipated impact of wind-energy development has been large-scale mortality of insectivorous bats. In eastern North America, where mortality rates are among the highest in the world, the hoary bat (Lasiurus cinereus) and the eastern red bat (L. borealis) comprise the majority of turbine-associated bat mortality. Both species are migratory tre...

It remains difficult to assess the timing and amount of atmospherically deposited and microbial nitrate (NO3-NAtm and NO3-NMicro, respectively) reaching streams. To elucidate temporal variation of NO3-NAtm and NO3-NMicro, we measured nitrate concentrations, δ17O-NO3-, and δ18O-NO3- in a stream draining a gaged, forested watershed in the central App...

Before their rapid expansion during the late Miocene, C4 plants were generally uncommon or absent from most grasslands. Recent studies have furthered our understanding of shifts in C4 abundance prior to their late-Miocene expansion; however, the early history of C4 grasses remains poorly constrained. Distinguishing C4 grasses from C3 taxa (i.e., mo...

Knowledge of the distribution and movements of populations of migratory birds is useful for the effective conservation and management of biodiversity. However, such information is often unavailable because of the difficulty of tracking sufficient numbers of individuals. We used more easily obtained feather stable hydrogen isotope ratios (δ2H) to pr...

Bats face numerous threats associated with global environmental change, including the rapid expansion of wind-energy facilities, emerging infectious disease, and habitat loss. An understanding of the movement and migration patterns of these highly dispersive animals would help reveal how spatially localized the impacts from these threats are likely...

Various environmental factors, including atmospheric CO2 (pCO(2)), regional climate, and fire, have been invoked as primary drivers of long-term variation in C-4 grass abundance. Evaluating these hypotheses has been difficult because available paleorecords often lack information on past C-4 grass abundance or potential environmental drivers. We ana...

Background/Question/Methods The Pleistocene-Holocene transition in North America (17,000 BP to 8,000 BP) was a time of widespread environmental change, including the arrival of humans, the extinction of 35 genera of megafauna, and individualistic shifts in species’ ranges and abundances in response to climate change and melting ice sheets. The wi...

The C4-plant functional type is a major evolutionary and ecological success. However, the relative importance of environmental factors, such as climatic conditions and atmospheric CO2 concentrations, in driving the origin of C4 grasses in different parts of the world remains poorly understood. We determined the carbon-isotope composition of 612 ind...

This article documents the public availability of (i) genomic sequence data and 43 microsatellite loci for the bat species, Lasiurus borealis and Lasiurus cinereus; and (ii) complete mitochondrial and partial nuclear genomes for two jack species, Caranx ignobilis, Caranx melampygus. This article is protected by copyright. All rights reserved.

Differentiating C3 and C4 grass pollen in the paleorecord is difficult because of their morphological similarity. Using a spooling wire microcombustion device interfaced with an isotope ratio mass spectrometer, Single Pollen Isotope Ratio AnaLysis (SPIRAL) enables classification of grass pollen as C3 or C4 based upon δ13C values. To address several...

Background/Question/Methods Government initiatives designed to address global climate change have spurred the proliferation of wind energy projects in the United States and abroad. Although wind energy development represents a move toward reducing greenhouse gas emissions, an unanticipated impact has been widespread mortality of migratory tree ba...

Background/Question/Methods Golden eagles (Aquila chrysaetos) are apex predators and thought to have a large effect on the population dynamics of their prey, with follow-on effects on ecosystem-level processes. In eastern North America there is a small population of golden eagles (ca. 1,000-3,000 individuals) whose basic ecology, including migrat...

Background/Question/Methods Grass-dominated ecosystems cover one-third of Earth’s land surface, influence key biogeochemical processes, and serve as major food sources. A challenge in studying the response of grasslands to environmental change in paleorecords is that grass pollen generally has low taxonomic specificity, which means that pollen as...

The hydrogen isotope composition of terrestrial plant leaf wax in sediments is increasingly used as a paleoclimatic indicator. Modern calibration studies suggest that paleoclimatic interpretation of leaf wax δD values requires consideration of the differences in the apparent fractionation of hydrogen isotopes among different groups of plants. Howev...

Fires burning the vast grasslands and savannas of Africa significantly influence the global carbon cycle. Projecting the impacts of future climate change on fire-mediated biogeochemical processes in these dry tropical ecosystems requires understanding of how various climate factors influence regional fire regimes. To examine climate–vegetation–fire...

Background/Question/Methods Grass-dominated ecosystems cover one-third of Earth’s land surface, influence key biogeochemical processes, and serve as major food sources. A challenge in studying the response of grasslands to environmental change in paleorecords is that grass pollen generally has low taxonomic specificity, which means that pollen as...

Background/Question/Methods Soil microbial communities influence a host of biogeochemical processes. An understanding of the factors regulating their composition may improve our ability to project changes in ecosystem function. Recent studies demonstrate that soil microbial communities are strongly influenced by soil pH. However, whether the infl...

There is limited evidence on how shifts in plant physiological performance influence vegetation variations in the paleorecord. To evaluate δ¹³C of pollen from C₃ plants as an indicator of community-level physiology, small quantities (10-30 grains) of untreated pollen and sporopollenin from herbarium specimens of Ambrosia (A. tomentosa and A. psilos...

The reliability of paleoclimatic inferences from lake-sediment records rests on the understanding of how various sediment indicators respond to environmental changes. Despite the recent proliferation of paleoclimatic records, only a limited number of studies have rigorously evaluated potential indicators by comparing lake-sediment records with inst...

Percent of different archaeal lineages (identified in Figs. 2, S3) for which there was no statistical difference among plant/[CO2] combinations. The abbreviations are as follows: maize ambient [CO2] (Ma), maize elevated [CO2] (Me), soybean ambient [CO2] (Sa), and soybean elevated [CO2] (Se). Mean values (+/− one standard deviation) are shown. (TIF)

Phylogenetic trees of amoA rRNA gene sequences from rhizosphere soil samples for each plant/[CO2] combination. The colored bars represent the relative abundances of representative sequences from individual plots for each plant/[CO2] combination, as in Figs. 2, S3. Identical branch lengths are shown for all branches and leaves. (PDF)

Number of reads obtained per sample for each gene and Chao1 estimates. (PDF)

Archaea are important to the carbon and nitrogen cycles, but it remains uncertain how rising atmospheric carbon dioxide concentrations ([CO(2)]) will influence the structure and function of soil archaeal communities. We measured abundances of archaeal and bacterial 16S rRNA and amoA genes, phylogenies of archaeal 16S rRNA and amoA genes, concentrat...

Middle-Holocene (8 to 4 ka BP) warmth and aridity are well recorded in sediment archives from midcontinental North America. However, neither the climatic driver nor the seasonal character of precipitation during this period is well understood because of the limitations of available proxy indicators. For example, an important challenge is to disting...

C4 plants are widely successful in the grass-dominated ecosystems of tropical, subtropical, and warm-temperate regions, largely as a result of their ability to limit photorespiration and improve water-use efficiency. A widely held paradigm is that low (<∼400 ppm) atmospheric CO2 concentrations were an important factor selecting for the origin of C4...

Background/Question/Methods North American grasslands are of ecological, economic, and societal importance. However, climate-vegetation-fire relationships in grasslands remain poorly understood, and ecological knowledge from historical records may be inadequate for anticipating future environmental changes that exceed the range of observed variab...

Background/Question/Methods: In African grasslands and savannas, fire plays a key role in vegetational dynamics and biogeochemical cycling. Only a few fire records in Africa extend into the Last Glacial Maximum, and even fewer exist in Africa’s vast equatorial grassland. We report here two macro-charcoal (particles >180 µm) records spanning the las...

Neighbor-joining phylogenetic trees of amino acid sequences from fosmid 7–14 that were used to assess LGT, as described in the text. Sequences in bold represent those from Clostridium cluster IV. For CDS 11, 29, and 34 the conclusion of LGT based upon the neighbor-joining trees differed from that based upon maximum likelihood trees (as listed in Ta...

PCR assessment of the presence of fosmid 7–14 and 7–25 16S rDNA sequences in marine iguana fecal samples from five different marine iguanas (named 24, 10, 18, 26, and 19). Arrows point to the 1.4 and 1.5 kb markers, between which is the expected PCR product size. Lanes 1 and 10 are molecular weight ladders (M). Lanes 2–6 represent the samples. A fa...

Phylogenetic trees of archaeal 16S rRNA gene sequences from rhizosphere soil samples from maize grown at ambient and elevated [CO2]. The colored bars represent the relative abundances of representative sequences from individual plots for each [CO2] treatment. Each colored bar in each phylogenetic tree represents data from a different plot. Starting...