Methylmercury and methane production potentials in North Carolina Piedmont stream sediments

Methylated mercury (MeHg) can be produced by all microbes possessing the genes hgcA and hgcB, which can include sulfate-reducing bacteria (SRB), iron-reducing bacteria (FeRB), methane-producing archaea (MPA), and other anaerobic microbes. These microbial groups compete for substrates, including hydrogen and acetate. When sulfate is in excess, SRB can outcompete other anaerobic microbes. However, low concentrations of sulfate, which often occur in stream sediments, are thought to reduce the relative importance of SRB. Although SRB are regarded as the primary contributors of MeHg in many aquatic environments, their significance may not be universal, and stream sediments are poorly studied with respect to microbial Hg methylation. We evaluated suppression of methanogenesis by SRB and the potential contributions from SRB, MPA and other MeHg producing microbes (including FeRB) to the production of MeHg in stream sediments from the North Carolina Piedmont region. Lower methanogenesis rates were observed when SRB were not inhibited, however, application of a sulfate-reduction inhibitor stimulated methanogenesis. Greater MeHg production occurred when SRB were active. Other MeHg producing microbes (i.e., FeRB) contributed significantly less MeHg production than SRB. MPA produced MeHg in negligible amounts. Our results suggest that SRB are responsible for the majority of MeHg production and suppress methanogenesis in mid-order stream sediments, similar to other freshwater sediments. Further investigation is needed to evaluate the generality of these findings to streams in other regions, and to determine the mechanisms regulating sulfate and electron acceptor availability and other potential factors governing Hg methylation and methane production in stream sediments.     

Edge Effects on Species Composition and Exotic Species Abundance in the North Carolina Piedmont

Edges between forest and non-forest habitats often have significant effects on forest microclimate and resource availability, with corresponding effects on species composition and abundance. Exotic species are often increased in abundance near forest edges. This increase in abundance could be either because of the increase in resource availability near edges, or because of increased dispersal into forest edges. We measured species composition and a set of geospatial variables on transects at 66 edges in the North Carolina Piedmont in an attempt to distinguish between these two factors. Mantel tests show that species composition is significantly different in forest edges than in the forest interior, but that this effect only penetrates about 5 m into the forest. Indicator species analysis finds several species that are indicative of edge communities, including trumpet vine (Campsis radicans), two drought-tolerant oak species (Quercus stellata and Q. falcata), a serviceberry (Amelanchier arboreum), and a common exotic species, tree-of-heaven (Ailanthus altissima). Poisson regression techniques showed that in both the seedling and tree strata of the forest, exotic species increased in abundance on flat sites with a high potential seed source. Mapping predicted exotic species abundance onto the landscape. We find that large-scale variation in exotic species abundance is due mostly to variation in potential seed sources, while small-scale variation relates more to edaphic factors. Our results stress that both dispersal and environmental filters are important for determining exotic species abundance, but potentially the filters operate at different spatial scales.     

Effects of land use on water quality and aquatic biota of three North Carolina Piedmont streams

Three streams in the Piedmont ecoregion of North Carolina were studied to evaluate the effect of land use (forested, agricultural, urban) on water quality and aquatic biota. In comparison with the forested stream, there were few changes in water quality at the agricultural and urban streams. Suspended-sediment yield was greatest for the urban catchment and least at the forested catchment. Suspended-sediment concentrations during storm events followed this same pattern, but at low-moderate flows suspended-sediment concentrations were greatest at the agricultural site. Most nutrient concentrations were highest at the agricultural site, and the amount of available dissolved nitrogen was elevated at both the urban and agricultural sites. High concentrations of metals (totals) in the water column were sometimes observed at all sites, but maximum average concentrations were recorded at the urban site (especially Cr, Cu, and Pb). Maximum sediment metal concentrations, however, were not found at the urban site, but were usually recorded at the forested site. Only minor differences were noted between fish communities of the forested and agricultural sites, although both abundance and average size of some species increased at the agricultural site. The fish community at the urban site was characterized by low species richness, low biomass, and the absence of intolerant species.Invertebrate taxa richness, a biotic index, and the number of unique invertebrate species (found at only one site) indicated moderate stress (Fair water quality) at the agricultural site and severe stress (Poor water quality) at the urban site. At the agricultural site, declines in taxa richness within intolerant groups were partially offset by increases within tolerant groups. The agricultural stream had the highest abundance values, indicating enrichment. The urban site, however, was characterized by low species richness for most groups and very low abundance values. Analysis of seasonal patterns suggested detritus was the most important food source for invertebrates in the forested stream, while periphyton was of greater importance in the agricultural stream. Dominant macroinvertebrate groups shifted from Ephemeroptera at the forested site, to Chironomidae at the agricultural site, and Oligochaeta at the urban site. There was little between-site overlap in dominant species (8–7%), indicating that land use strongly influenced the invertebrate community. Chemical and physical parameters measured at the three sites did not seem sufficient to account for all of the observed differences in the invertebrate communities, suggesting some unmeasured toxicity. Biological measurements, especially macroinvertebrates community structure, consistently indicated strong between-site differences in water and habitat quality.     

Spatial Impacts of Stream and Wetland Restoration on Riparian Soil Properties in the North Carolina Piedmont

Hydric soil development of riparian wetlands is primarily influenced by the hydrologic connection between the floodplains and the stream channel. Often, the goal of riparian restoration is to revitalize this connectivity through a restructuring of the stream channel and the floodplain; however, the effects of this restructuring on the physical and spatial characteristics of soil properties are rarely considered. The objective of this study was to quantify the impacts of restoration efforts on the spatial characteristics of soil properties by means of a pre‐ and post‐restoration comparison. We determined that the spatial patterns of soil organic matter (SOM) and exchangeable phosphorus (P_ex) appeared less variable in the years following restoration than in the years before restoration. Mean SOM significantly decreased after restoration, whereas mean P_ex significantly increased. The spatial characteristics and mean concentrations of NO₂–NO₃ did not differ much between sampling dates. The loss of this spatial patterning in SOM and P_ex and the decrease in SOM pools may represent negative impacts of restoration on important ecosystem characteristics. This study demonstrates that soil properties and spatial patterns can be negatively affected by restoration activities potentially hindering ecosystem development and function.     

Bacterial Communities in the Rhizosphere of Biofuel Crops Grown on Marginal Lands as Evaluated by 16S rRNA Gene Pyrosequences

Microbes are key components of the soil environment and are important contributors to the sustainability of agricultural systems, which is especially significant for biofuel crops growing on marginal lands. We studied bacterial communities in the rhizosphere of five biofuel crops cultivated in four locations in Michigan to determine which factors were correlated to changes in the structure of those communities. Three of these sites were marginal lands in that two were not suitable for conventional agriculture and one was regulated as a brownfield due to prior industrial pollution. Bacterial community composition and structure were assessed by 454 sequencing of the 16S rRNA gene. A total of 387,111 sequences were used for multivariate statistical analysis and to test for correlation between community structure and environmental variables such as plant species, soil attributes, and location. The most abundant bacterial phyla found in the rhizosphere of all crops were Acidobacteria, Proteobacteria, Actinobacteria, and Verrucomicrobia. Bacterial communities grouped by location rather than by crop and their structures were correlated to soil attributes, principally pH, organic matter, and nutrients. The effect of plant species was low but significant, and interactions between locations, plant species, and soil attributes account for most of the explained variation in the structure of bacterial communities, showing a complex relationship between bacterial populations and their environment. Bacterial diversity was higher in the agricultural sites compared to adjacent forest sites, indicating that the cultivation of those biofuel crops increased the rRNA diversity.     

The Effect of Forest Type on Benthic Macroinvertebrate Structure and Ecological Function in a Pine Plantation in the North Carolina Piedmont

We examined the impact of small-scale commercial forestry on the structure and function of 6 headwater streams in the North Carolina Piedmont. During 2001–2003 terrestrial organic matter inputs, temperature, macroinvertebrate community composition and tolerance, leaf breakdown rate, and food web structure were quantified for 2 streams draining mature stands of managed loblolly pine, 2 streams draining mature hardwood forests, and 2 streams draining 3-year-old clear cuts, which had been replanted with loblolly pine. Streams in the clear-cuts and pine plantations were bordered by a 15 m hardwood buffer. Despite differences in watershed land-use, there were no significant differences in the organic matter supply or temperature between streams draining different forest types. However, algal biomass was significantly higher in clear-cut sites than forested sites, and was also higher in hardwood sites than pine sites. Streams draining the clear-cut sites contained lower macroinvertebrate richness and diversity, and fewer intolerant species, than streams draining pine and hardwood stands. Despite the differences in macroinvertebrates community composition, there was no difference among forest types in leaf-pack breakdown rates. Analysis of δ¹⁵N and δ¹³C natural abundance of functional feeding group indicated that the shredders and predators collected from streams draining clear-cuts had a δ¹⁵N value that was enriched relative to the macroinvertebrates of streams draining pine and hardwood forests. This difference in δ¹⁵N signature appears to be the result of the incorporation of riparian grass species in the clear-cuts, which have a higher δ¹⁵N, into the diet of shredders. Pine sites had similar food webs to natural hardwood sites. Our results suggest that clear-cutting changes both the trophic dynamics and macroinvertebrate composition of low-order Piedmont streams in North Carolina despite the presence of hardwood buffers. However, large differences were not found between older pine and hardwood stands, indicating rapid recovery following re-growth of forest vegetation, when hardwood buffer strips were present.     

Patterns of trombiculid mite (Hannemania dunni) parasitism among plethodontid salamanders in the western Piedmont of North Carolina

Trombiculid mites are known to parasitize a variety of amphibian species, yet few comparisons of mite parasitism among amphibian species have been made. In this study, we investigated patterns of trombiculid mite parasitism among 3 plethodontid salamanders (Desmognathus fuscus, Eurycea cirrigera, and Plethodon cylindraceus) in the western Piedmont of North Carolina. All 3 salamander species were parasitized by a single species, Hannemania dunni. Desmognathus fuscus harbored mites more frequently (60.4% of individuals) than E. cirrigera (11.1%) or P. cylindraceus (14.6%). Desmognathus fuscus also had higher parasite loads than E. cirrigera or P. cylindraceus (P < 0.001). Mites on D. fuscus were found more frequently on the limbs than other body locations (P < 0.001). We found no correlation between salamander size and mite abundance (P = 0.689), but salamander collection sites influenced the abundance of mites on D. fuscus (P = 0.002). We found no effect of season on mite abundance in D. fuscus (P = 0.952). Salamander habitat preferences and edaphic or climatic differences among study sites may influence patterns of Hannemania sp. parasitism of salamanders.     

Wetmore on the Birds of North Carolina

[Notes on the Birds of North Carolina. By Alexander Wetmore. Proc. U.S. Nat. Mus. vol. xc. pp. 483–530 (1941).]     

Changes in forest structure, species diversity and spatial pattern following hurricane disturbance in a Piedmont North Carolina forest, USA

Aims: Large hurricanes have profound impacts on temperate forests,but owing to their infrequent nature these effects have rarelybeen examined in detail. In 1996, Hurricane Fran significantlydamaged many long-term tree census plots in the Duke Foreston the North Carolina Piedmont, thereby providing an exceptionalopportunity to examine pre- and post-hurricane forest compositionaltrajectories. Our goal was to examine immediate, short-term(0–4 years) and longer term (5 year) hurricane-inducedstructural, spatial and compositional changes in the tree population(stem d.b.h > 1 cm) in the context of our detailed, long-termknowledge of the dynamics of these forests. Methods: We surveyed stem damage and tree mortality in 34 long-term permanentplots (ca. 70-year record; 404–1 012 m²) and 7 large mappedtree stands (ca. 20-year record; 5 250–65 000 m²) representingboth transition-phase, even-aged pine stands and uneven-agedupland hardwood forests. We employed three types of damage measuresto quantify stand-level damage severity: percentage of stemsdamaged, percentage of basal area lost and a ‘stand-leveldamage index’. Second-order spatial analysis (Ripley'sK-function) was used to investigate patterns in tree mortality. Important findings: Our study found hurricane effects on the structural attributesof Piedmont forests to be variable and patchy. Changes in treespecies composition, however, were modest. Uprooting was themajor damage type for the overstory trees [diameter at breastheight (d.b.h.) >10 cm] apparently due to the exposure ofthe crowns to high wind combined with heavy rainfall prior toand during the storm. Saplings, juvenile trees and small trees(1–10 cm d.b.h.) of the understory and midstory were mainlydamaged by being pinned or bent by their damaged large neighbors.Hurricane-induced tree mortality varied weakly among species,was positively correlated with pre-hurricane tree size and remainedup to 2-fold higher than pre-hurricane background mortality5 years after the hurricane. Spatial point pattern analysisrevealed a patchy distribution of tree mortality during thehurricane sampling interval. Hurricane Fran resulted in a dramaticincrease in average gap size from ca. 400 m² pre-hurricane toca 1100 m² after the hurricane, whereas maximum gap sizes reached18–34 times larger than the pre-hurricane levels.     

Effects of Initial Site Treatments on Early Growth and Three-Year Survival of Idaho Fescue

Prairies in the Pacific Northwest have been actively restored for over a decade. Competition from non‐native woody and herbaceous species has been presumed to be a major cause for the failure of restoration projects. In this research, plugs of the native prairie bunchgrass, Festuca idahoensis Elmer var. roemeri (Pavlick), were grown from seed in a nursery and transplanted into a grassland site dominated by non‐native pasture grasses. The growth of the plants was followed for three years, and biomass of all volunteer plants was measured. Before planting, five treatments were applied to the plots: removal of vegetation by burning, removal of vegetation by an herbicide‐and‐till procedure, soil impoverishment by removal of organic matter, fertilizer application, and compost mulch application. Initial growth of Idaho fescue plugs was greatest with fertilizer and compost mulch. Plants grown in mulched plots were also able to photosynthesize later into the dry summer season. After the first year, plots initially fertilized or composted had the lowest survival rate of Idaho fescue. Impoverished and herbicide‐and‐till plots had the greatest 3‐year survival. Mulched plots supported the greatest weed growth after three years. Stressful environments give a competitive advantage to Idaho fescue in prairie restoration projects. As weedy species increase, growth and survival of Idaho fescue decreases.     

Systematics of dusky salamanders, Desmognathus (Caudata: Plethodontidae), in the mountain and Piedmont regions of Virginia and North Carolina, USA

We analysed mitochondrial (cytochrome  b ) nucleotide sequences, nuclear allozyme markers, and morphometric characters to investigate species boundaries and phylogenetic relationships among dusky salamanders ( Desmognathus ) in the southern Blue Ridge and adjacent Piedmont Physiographic Provinces of Virginia and North Carolina. Our results revealed four distinct mitochondrial DNA clades that are also characterized by distinct allozyme markers. One clade consists of sequences derived from populations distributed from New England to south-western Virginia that are referable to Desmognathus fuscus Rafinesque, 1820, although there is considerable sequence and allozyme divergence within this clade. A second clade consists of sequences derived from populations referable to Desmognathus planiceps Newman, 1955, a form that we resurrect from its long synonymy under D. fuscus . Desmognathus planiceps and D. fuscus also differ in mandibular tooth shape. Two other cytochrome  b sequences recovered from populations along the Blue Ridge escarpment in southern Virginia are quite divergent from those of the previous two clades, and these populations may represent yet another distinct species. Sequences from a population in the Brushy Mountains in the Piedmont of northern North Carolina are similar to those of Desmognathus carolinensis . Population groupings indicated by allozyme data generally correspond to the cytochrome  b clades. Cryptic diversity in Appalachian desmognathan salamanders clearly requires further study. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 115–130.     

Effects of Flooding Regime and Seedling Treatment on Early Survival and Growth of Nuttall Oak

Effects of flooding on survival and growth of three different types of Nuttall oak (Quercus texana Buckl.) seedlings were observed at the end of third and fifth growing seasons at Yazoo National Wildlife Refuge, Mississippi, U.S.A. Three types of seedlings were planted in January 1995 in a split‐plot design, with four replications at each of two elevations on floodprone, former cropland in Sharkey clay soil. The lower of the two planting elevations was inundated for 21 days during the first growing season, whereas the higher elevation did not flood during the 5‐year period of this study. The three types of 1‐0 seedlings were bareroot seedlings, seedlings grown in containers (3.8 × 21–cm plastic seedling cones), and container‐grown seedlings inoculated with vegetative mycelia of Pisolithus tinctorius (Pers.) Coker. Survival of all the three seedling types was greatest at the lower, intermittently flooded elevation, indicating that drought and related effects on plant competition were more limiting to seedling survival than flooding. At the lower elevation, survival of mycorrhizal‐inoculated container seedlings was greater than that of noninoculated container seedlings. Survival among bareroot seedlings and inoculated container seedlings was not significantly different at either elevation. At the higher, nonflooded elevation, however, bareroot seedling survival was greater than the survival of container seedlings without inoculation. Differences were significant among the inoculated and the noninoculated container seedlings, with higher survival of inoculated seedlings at both elevations, though differences were only significant in year 3. At the end of the fifth year, height of bareroot seedlings was significantly greater than the heights of both types of container‐grown seedlings at both planting elevations. Because seedlings grown in the plastic seedlings cones did not survive better than the bareroot seedlings at either planting elevation, the bareroot stock appear to be the economically superior choice for regeneration in Sharkey soil.     

Genealogical Relationships between Early Medieval and Modern Inhabitants of Piedmont

In the period between 400 to 800 AD, also known as the period of the Barbarian invasions, intense migration is documented in the historical record of Europe. However, little is known about the demographic impact of these historical movements, potentially ranging from negligible to substantial. As a pilot study in a broader project on Medieval Europe, we sampled 102 specimens from 5 burial sites in Northwestern Italy, archaeologically classified as belonging to Lombards or Longobards, a Germanic people ruling over a vast section of the Italian peninsula from 568 to 774. We successfully amplified and typed the mitochondrial hypervariable region I (HVR-I) of 28 individuals. Comparisons of genetic diversity with other ancient populations and haplotype networks did not suggest that these samples are heterogeneous, and hence allowed us to jointly compare them with three isolated contemporary populations, and with a modern sample of a large city, representing a control for the effects of recent immigration. We then generated by serial coalescent simulations 16 millions of genealogies, contrasting a model of genealogical continuity with one in which the contemporary samples are genealogically independent from the medieval sample. Analyses by Approximate Bayesian Computation showed that the latter model fits the data in most cases, with one exception, Trino Vercellese, in which the evidence was compatible with persistence up to the present time of genetic features observed among this early medieval population. We conclude that it is possible, in general, to detect evidence of genealogical ties between medieval and specific modern populations. However, only seldom did mitochondrial DNA data allow us to reject with confidence either model tested, which indicates that broader analyses, based on larger assemblages of samples and genetic markers, are needed to understand in detail the effects of medieval migration.     

Management of Warm- and Cool-Season Grasses for Biomass on Marginal Lands: II. Composition and Nutrient Balance

Organic fertilizers can improve soil health while providing nutrients for perennial grass growth for bioenergy feedstock, particularly under marginal soil conditions. The impact of organic fertilizer application on perennial grass composition needs clarification. Our objective was to evaluate feedstock composition, and N, P, and K dynamics of switchgrass (Panicum virgatum L.), tall fescue [Lolium arundinaceum (Schreb.)], and reed canarygrass (Phalaris arundinacea L.) provided with either inorganic or organic fertilizer sources. Grasses were established on a sandy soil and a clay soil at the Cornell University Willsboro Research Farm in Willsboro, NY. The experiment was a split-split plot randomization of a randomized block design with six replicates. Sites were whole plots, grass species were subplots, and fertility treatments were sub-subplots. Six treatments were (1) 168 kg ha^?1 of N fertilizer for cool-season grasses; 84 kg ha^?1 for switchgrass, (2) 56 kg ha^?1 of 0-46-0 P fertilizer plus N (#1), (3) 112 kg ha^?1 of 0-0-60 K fertilizer plus N (#1), (4) 89.6 Mg dairy manure ha^?1, (5) 44.8 Mg dairy manure compost ha^?1, and (6) a control without fertilizer. Organic fertilizers produced a net positive P and K balance, while other treatments had negative balances. Organic fertilizer treatments resulted in lower lignin and gross energy values, and higher total ash and Cl, compared to inorganic fertilizer treatments. Switchgrass biomass had higher fiber and gross energy, lower total ash, and much lower Cl content under organic fertilizer applications than cool-season grasses, making switchgrass a more desirable feedstock regardless of conversion process.     

Effects of Stream Restoration on Woody Riparian Vegetation of Southern Appalachian Mountain Streams,North Carolina,U.S.A

Riparian revegetation, such as planting woody seedlings or live stakes, is a nearly ubiquitous component of stream restoration projects in the United States. Though evaluations of restoration success usually focus on in‐stream ecosystems, in order to understand the full impacts of restoration the effects on riparian ecosystems themselves must be considered. We examined the effects of stream restoration revegetation measures on riparian ecosystems of headwater mountain streams in forested watersheds by comparing riparian vegetation structure and composition at reference, restored, and degraded sites on nine streams. According to mixed model analysis of variance (ANOVA), there was a significant effect of site treatment on riparian species richness, basal area, and canopy cover, but no effect on stem density. Vegetation characteristics at restored sites differed from those of reference sites according to all metrics (i.e. basal area, canopy cover, and species composition) except species richness and stem density. Restored and degraded sites were structurally similar, with some overlap in species composition. Restored sites were dominated by Salix sericea and Cornus amomum (species commonly planted for revegetation) and a suite of disturbance‐adapted species also dominant at degraded sites. Differences between reference and restored sites might be due to the young age of restored sites (average 4 years since restoration), to reassembly of degraded site species composition at restored sites, or to the creation of a novel anthropogenic ecosystem on these headwater streams. Additional research is needed to determine if this anthropogenic riparian community type persists as a resilient novel ecosystem and provides valued riparian functions.     

Growth,reproduction, and feeding oF Fundulus heteroclitus (L.) on a North Carolina salt marsh

Fundulus heteroclitus (L.) from a North Carolina Spartina marsh teed largely on small crustaceans (amphipods, tanaids and copepods) and polychaetes. Fish longer than 30 mm standard length also ingested considerable amounts of living plant material. Smaller individuals were distinctly carnivorous. Recognizable particles of Spartina detritus occurred in less than 15% of the guts examined. The relationship of weight to length changed significantly during the year. Although females were larger than males of the same age. males were heavier than females of the same length, except for a brief period at the peak of the spawning season in the early spring. An average second season fish may lay up to 512 eggs from March through August, but first season fish did not reach reproductive size by the end of the spawning season. Growth of first season fish in mid-summer averaged 5% of their total weight per day. These significant seasonal changes in ecological properties of killifish populations are important in any estimates of growth, reproduction, and production.     

Interactions Between Competition and Predation Shape Early Growth and Survival of Two Neotropical Hylid Tadpoles

Experimental studies in temperate regions have revealed that competition and predation interact to shape aquatic communities. Predators typically reduce the effect of competition on growth and competitors provide alternative prey subjects, which may also alter predation. Here, we examine the independent and combined effects of competition and predation on the survival and growth of hatchling tadpoles of two widespread co‐occurring Neotropical hylid frogs (Agalychnis callidryas and Dendropsophus ebraccatus). Using 400 L mesocosms, we used a 2 × 3 factorial substitutive design, which crossed tadpole species composition with the presence or absence of a free‐roaming predator (Anax amazili dragonfly larva). Dragonflies were effective predators of both species, but had larger effects on A. callidryas survival. Both species had similar growth rates when alone, whereas A. callidryas grew 30 percent faster than D. ebraccatus when they co‐occurred, suggesting interspecific rather than intraspecific competition had relatively stronger effects on D. ebraccatus growth, while the opposite was true for A. callidryas. Predator presence dramatically reduced growth rates of both species and erased this asymmetry. Results suggest that the effects of predator induction (i.e., nonconsumptive effects) on growth were larger than both consumptive and competitive effects. Our study demonstrates that predators have strong effects on both survival and growth of prey, highlighting the potential importance of predators in shaping prey populations and tropical aquatic food web interactions. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Changes in the Rooting and Growth of Willows and Poplars Induced by Cadmium

Growth parameters of six fast growing trees showed that the roots responded to Cd treatment more sensitively than the shoots. Cd-treatment suppressed rooting and root growth (length and biomass production) as well as its development in all tested species. Root systems of Salix cinerea, Salix alba, and Populus cv. Robusta were more tolerant to Cd stress than the root system of the other studied species. Shoot growth parameters of Salix species were significantly reduced unlike Populus species, which were not affected by Cd treatment.