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Item Open Access Above-ground biomass and structure of 260 African tropical forests.(Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 2013-01) Lewis, Simon L; Sonké, Bonaventure; Sunderland, Terry; Begne, Serge K; Lopez-Gonzalez, Gabriela; van der Heijden, Geertje MF; Phillips, Oliver L; Affum-Baffoe, Kofi; Baker, Timothy R; Banin, Lindsay; Bastin, Jean-François; Beeckman, Hans; Boeckx, Pascal; Bogaert, Jan; De Cannière, Charles; Chezeaux, Eric; Clark, Connie J; Collins, Murray; Djagbletey, Gloria; Djuikouo, Marie Noël K; Droissart, Vincent; Doucet, Jean-Louis; Ewango, Cornielle EN; Fauset, Sophie; Feldpausch, Ted R; Foli, Ernest G; Gillet, Jean-François; Hamilton, Alan C; Harris, David J; Hart, Terese B; de Haulleville, Thales; Hladik, Annette; Hufkens, Koen; Huygens, Dries; Jeanmart, Philippe; Jeffery, Kathryn J; Kearsley, Elizabeth; Leal, Miguel E; Lloyd, Jon; Lovett, Jon C; Makana, Jean-Remy; Malhi, Yadvinder; Marshall, Andrew R; Ojo, Lucas; Peh, Kelvin S-H; Pickavance, Georgia; Poulsen, John R; Reitsma, Jan M; Sheil, Douglas; Simo, Murielle; Steppe, Kathy; Taedoumg, Hermann E; Talbot, Joey; Taplin, James RD; Taylor, David; Thomas, Sean C; Toirambe, Benjamin; Verbeeck, Hans; Vleminckx, Jason; White, Lee JT; Willcock, Simon; Woell, Hannsjorg; Zemagho, LiseWe report above-ground biomass (AGB), basal area, stem density and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy tropical forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha⁻¹ (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha⁻¹) similar to those of Bornean forests, and significantly greater than East or West African forests. AGB therefore appears generally higher in palaeo- compared with neotropical forests. However, mean stem density is low (426 ± 11 stems ha⁻¹ greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean forests (cf. approx. 600) and is the signature structural feature of African tropical forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationships with C : N ratio (suggesting a positive soil phosphorus-AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy tropical forests may be particularly sensitive to future precipitation and temperature changes.Item Open Access Accumulation and Distribution of Trace Elements and Radionuclides in Agricultural Soils Impacted from Long-term Phosphate Fertilizer Application(2023-04-20) Hu, JunExcessive application of phosphate fertilizers can result in the accumulation of both phosphorus (P) and trace metals (U, Cd) in agricultural soils, which could end up in crops and cause chronic harms to the environment. Here we investigate the quality of soils in a long-term trial corn/soybean field at the Tidewater Research Station, North Carolina, where both surface soils (top 20 cm) and subsurface soils (up to 150 cm) were collected from five plots with different application rates of P-fertilizer since 1966. We analyzed a broad range of major nutrients and trace elements with focus on metals and metalloids including Cd, U, V, Cr, As, and Sr, which are notably enriched in the used P-fertilizer relative to local background soil. The study aims to investigate the trace elements accumulation, distribution, and mobilization in the soils. The results show that the impact of long-term P-fertilizer application was mostly manifested in the top layers of the soils compared to deeper soils, with the exception of As showing accumulation in the deeper soils. Among the five plots, bulk soils applied with higher rates of P-fertilizers had higher concentrations of P and trace elements than soils without using P-fertilizers. The concentration of Cd was significantly correlated with that of P (r = 0.97, p = 0.005) in the bulk surface soils, indicative of its direct contribution from P-fertilizer and accumulation in the soil. In contrast, other trace elements exhibited weaker or little correlations with P in the bulk surface soils. The potential bioavailability of elements in soils was assessed via the Mehlich III extraction method, showing that the higher application rate of P-fertilizer, the higher percent of bioavailability was found for Cd (up to 65% of the bulk soil) and P (up to 56%), whereas the other trace elements had much lower bioavailable fractions (0.4 – 12%). Strong correlations (r > 0.9, p < 0.05) were observed between the bioavailable concentrations of P and that of Cd, U, Cr, V, As, Sr in the surface soils. This indicates that the bioavailable form of trace elements is more sensitive in reflecting the impacts from P- fertilizer on surface soils. Four-step sequential leaching tests (i.e., F1: exchangeable, F2: reducible, F3: oxidizable, and F4: residual) conducted for the surface soils indicated differential mobilization of trace elements under different P-fertilizers application rates. Greater portions of Cd were found in the mobile fractions (F1 – F3) of soils with higher P-fertilizer input, while Sr was dominantly present in the residual fraction (F4: 95 – 97%), and redox-sensitive elements were higher in the reducible (As, V) and oxidizable (U, Cr) fractions than Sr, reflecting their redox-dependent mobilization potential. Overall, our systematic data analysis shows the effect of long-term P-fertilizer application on the accumulation of trace elements in soils. Further studies should evaluate the uptake of trace elements by crops and their mobilization to the underlying groundwater resources.Item Open Access Contingency in ecosystem but not plant community response to multiple global change factors(New Phytologist, 2012) Bradford, MA; Wood, SA; Maestre, FT; REYNOLDS, JF; Warren, RJCommunity and ecosystem responses to global environmental change are contingent on the magnitude of change and interacting global change factors. To reveal whether responses are also contingent on the magnitude of each interacting factor, multifactor, multilevel experiments are required, but are rarely conducted. We exposed model grassland ecosystems to six levels of atmospheric CO2 and six levels of nitrogen enrichment, applying the latter both chronically (simulating deposition) and acutely (simulating fertilization). The 66 treatments were maintained for 6 months under controlled growing conditions, with biomass harvested every 28 d and sorted to species. Aboveground plant productivity responses to CO2 were contingent on nitrogen amount, and the responses to nitrogen amount were dependent on whether applications were chronic or acute. Specifically, productivity responses to increasing CO2 concentrations were accentuated with higher nitrogen enrichments, and productivity was greater when higher nitrogen enrichments were applied acutely. Plant community composition was influenced only by nitrogen enrichment, where the co-dominant grass species with the greatest leaf trait plasticity increasingly dominated with higher nitrogen amounts. Community processes are considered to be unpredictable, but our data suggest that the prediction of the impacts of simultaneous global changes is more complex for ecosystem processes, given that their responses are contingent on the levels of interacting factors.Item Open Access Development and deployment of a field-portable soil O2 and CO2 gas analyzer and sampler.(PloS one, 2019-01) Brecheisen, Zachary S; Cook, Charles W; Heine, Paul R; Ryang, Junmo; Richter, Daniel deBHere we present novel method development and instruction in the construction and use of Field Portable Gas Analyzers study of belowground aerobic respiration dynamics of deep soil systems. Our Field-Portable Gas Analysis (FPGA) platform has been developed at the Calhoun Critical Zone Observatory (CCZO) for the measurement and monitoring of soil O2 and CO2 in a variety of ecosystems around the world. The FPGA platform presented here is cost-effective, lightweight, compact, and reliable for monitoring dynamic soil gasses in-situ in the field. The FPGA platform integrates off-the-shelf components for non-dispersive infrared (NDIR) CO2 measurement and electro-chemical O2 measurement via flow-through soil gas analyses. More than 2000 soil gas measurements have been made to date using these devices over 4 years of observations. Measurement accuracy of FPGAs is consistently high as validated via conventional bench-top gas chromatography. Further, time series representations of paired CO2 and O2 measurement under hardwood forests at the CCZO demonstrate the ability to observe and track seasonal and climatic patterns belowground with this FPGA platform. Lastly, the ability to analyze the apparent respiratory quotient, the ratio of apparent CO2 accumulation divided by apparent O2 consumption relative to the aboveground atmosphere, indicates a high degree of nuanced analyses are made possible with tools like FPGAs. In sum, the accuracy and reliability of the FPGA platform for soil gas monitoring allows for low-cost temporally extensive and spatially expansive field studies of deep soil respiration.Item Open Access Differential nutrient limitation of soil microbial biomass and metabolic quotients (qCO2): is there a biological stoichiometry of soil microbes?(PLoS One, 2013) Hartman, Wyatt H; Richardson, Curtis JBACKGROUND: Variation in microbial metabolism poses one of the greatest current uncertainties in models of global carbon cycling, and is particularly poorly understood in soils. Biological Stoichiometry theory describes biochemical mechanisms linking metabolic rates with variation in the elemental composition of cells and organisms, and has been widely observed in animals, plants, and plankton. However, this theory has not been widely tested in microbes, which are considered to have fixed ratios of major elements in soils. METHODOLOGY/ PRINCIPAL FINDINGS: To determine whether Biological Stoichiometry underlies patterns of soil microbial metabolism, we compiled published data on microbial biomass carbon (C), nitrogen (N), and phosphorus (P) pools in soils spanning the global range of climate, vegetation, and land use types. We compared element ratios in microbial biomass pools to the metabolic quotient qCO2 (respiration per unit biomass), where soil C mineralization was simultaneously measured in controlled incubations. Although microbial C, N, and P stoichiometry appeared to follow somewhat constrained allometric relationships at the global scale, we found significant variation in the C∶N∶P ratios of soil microbes across land use and habitat types, and size-dependent scaling of microbial C∶N and C∶P (but not N∶P) ratios. Microbial stoichiometry and metabolic quotients were also weakly correlated as suggested by Biological Stoichiometry theory. Importantly, we found that while soil microbial biomass appeared constrained by soil N availability, microbial metabolic rates (qCO2) were most strongly associated with inorganic P availability. CONCLUSIONS/ SIGNIFICANCE: Our findings appear consistent with the model of cellular metabolism described by Biological Stoichiometry theory, where biomass is limited by N needed to build proteins, but rates of protein synthesis are limited by the high P demands of ribosomes. Incorporation of these physiological processes may improve models of carbon cycling and understanding of the effects of nutrient availability on soil C turnover across terrestrial and wetland habitats.Item Open Access Environmental conditions influence the plant functional diversity effect on potential denitrification.(PLoS One, 2011-02-02) Sutton-Grier, Ariana E; Wright, Justin P; McGill, Bonnie M; Richardson, CurtisGlobal biodiversity loss has prompted research on the relationship between species diversity and ecosystem functioning. Few studies have examined how plant diversity impacts belowground processes; even fewer have examined how varying resource levels can influence the effect of plant diversity on microbial activity. In a field experiment in a restored wetland, we examined the role of plant trait diversity (or functional diversity, (FD)) and its interactions with natural levels of variability of soil properties, on a microbial process, denitrification potential (DNP). We demonstrated that FD significantly affected microbial DNP through its interactions with soil conditions; increasing FD led to increased DNP but mainly at higher levels of soil resources. Our results suggest that the effect of species diversity on ecosystem functioning may depend on environmental factors such as resource availability. Future biodiversity experiments should examine how natural levels of environmental variability impact the importance of biodiversity to ecosystem functioning.Item Open Access Environmental fate and effects of Bacillus thuringiensis (Bt) proteins from transgenic crops: a review.(Journal of agricultural and food chemistry, 2005-06) Clark, BW; Phillips, TA; Coats, JRThis paper reviews the scientific literature addressing the environmental fate and nontarget effects of the Cry protein toxins from Bacillus thuringiensis (Bt), specifically resulting from their expression in transgenic crops. Published literature on analytical methodologies for the detection and quantification of the Cry proteins in environmental matrices is also reviewed, with discussion of the adequacy of the techniques for determining the persistence and mobility of the Bt proteins. In general, assessment of the nontarget effects of Bt protein toxins indicates that there is a low level of hazard to most groups of nontarget organisms, although some investigations are of limited ecological relevance. Some published reports on the persistence of the proteins in soil show short half-lives, whereas others show low-level residues lasting for many months. Improvements in analytical methods will allow a more complete understanding of the fate and significance of Bt proteins in the environment.Item Open Access Estimation of in-canopy ammonia sources and sinks in a fertilized Zea mays field.(Environ Sci Technol, 2010-03-01) Bash, JO; Walker, JT; Katul, GG; Jones, MR; Nemitz, E; Robarg, WPAn analytical model was developed to describe in-canopy vertical distribution of ammonia (NH(3)) sources and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy mean NH(3) concentration and wind speed profiles. This model was applied to quantify in-canopy air-surface exchange rates and above-canopy NH(3) fluxes in a fertilized corn (Zea mays) field. Modeled air-canopy NH(3) fluxes agreed well with independent above-canopy flux estimates. Based on the model results, the urea fertilized soil surface was a consistent source of NH(3) one month following the fertilizer application, whereas the vegetation canopy was typically a net NH(3) sink with the lower portion of the canopy being a constant sink. The model results suggested that the canopy was a sink for some 70% of the estimated soil NH(3) emissions. A logical conclusion is that parametrization of within-canopy processes in air quality models are necessary to explore the impact of agricultural field level management practices on regional air quality. Moreover, there are agronomic and environmental benefits to timing liquid fertilizer applications as close to canopy closure as possible. Finally, given the large within-canopy mean NH(3) concentration gradients in such agricultural settings, a discussion about the suitability of the proposed model is also presented.Item Open Access Evolution of Edaphic Ecology in Ceanothus (Rhamnaceae)(2011) Burge, Dylan O.Edaphic factors--those pertaining to the substrate or soil--are thought to play an important role in the diversification of flowering plants. Although edaphic factors are widely interpreted as causal agents in plant diversification, little is known about the evolutionary origin of most edaphic endemic plants, preventing inference of potential mechanisms by which substrate properties may influence speciation. The North American plant genus Ceanothus (Rhamnaceae) contains 9 edaphic-endemic species, taxa restricted to soils derived from specific geological materials. The three components of my dissertation research aim to improve understanding of how edaphic ecology has influenced the diversification of Ceanothus. First, I use DNA sequence data from the low-copy nuclear gene nitrate reductase to reconstruct the phylogeny of Ceanothus and elucidate diversification of this group into the California Floristic Province (CFP) of western North America, including the evolution of edaphic endemism. This research indicates that diversification of the two Ceanothus subgenera (Cerastes and Ceanothus) is centered on the CFP and is characterized by shallow divergence and phylogenetic relationships defined predominantly by geography. Divergence time estimation suggests that diversification of both Ceanothus subgenera began approximately 6 Ma. The nine edaphic-endemic taxa are not phylogenetically clustered in my analyses, suggesting that the origin of edaphic endemism has occurred on multiple occasions, including multiple examples of serpentine endemism. The second chapter of my dissertation uses soil chemistry data in combination with a more detailed examination of genetic variation in nitrate reductase to elucidate the evolution of a single edaphic endemic species.
Item Open Access Four-decade responses of soil trace elements to an aggrading old-field forest: B, Mn, Zn, Cu, and Fe.(Ecology, 2008-10) Li, Jianwei; Richter, Daniel D; Mendoza, Arlene; Heine, PaulIn the ancient and acidic Ultisol soils of the Southern Piedmont, USA, we studied changes in trace element biogeochemistry over four decades, a period during which formerly cultivated cotton fields were planted with pine seedlings that grew into mature forest stands. In 16 permanent plots, we estimated 40-year accumulations of trace elements in forest biomass and O horizons (between 1957 and 1997), and changes in bioavailable soil fractions indexed by extractions of 0.05 mol/L HCl and 0.2 mol/L acid ammonium oxalate (AAO). Element accumulations in 40-year tree biomass plus O horizons totaled 0.9, 2.9, 4.8, 49.6, and 501.3 kg/ha for Cu, B, Zn, Mn, and Fe, respectively. In response to this forest development, samples of the upper 0.6-m of mineral soil archived in 1962 and 1997 followed one of three patterns. (1) Extractable B and Mn were significantly depleted, by -4.1 and -57.7 kg/ha with AAO, depletions comparable to accumulations in biomass plus O horizons, 2.9 and 49.6 kg/ha, respectively. Tree uptake of B and Mn from mineral soil greatly outpaced resupplies from atmospheric deposition, mineral weathering, and deep-root uptake. (2) Extractable Zn and Cu changed little during forest growth, indicating that nutrient resupplies kept pace with accumulations by the aggrading forest. (3) Oxalate-extractable Fe increased substantially during forest growth, by 275.8 kg/ha, about 10-fold more than accumulations in tree biomass (28.7 kg/ha). The large increases in AAO-extractable Fe in surficial 0.35-m mineral soils were accompanied by substantial accretions of Fe in the forest's O horizon, by 473 kg/ha, amounts that dwarfed inputs via litterfall and canopy throughfall, indicating that forest Fe cycling is qualitatively different from that of other macro- and micronutrients. Bioturbation of surficial forest soil layers cannot account for these fractions and transformations of Fe, and we hypothesize that the secondary forest's large inputs of organic additions over four decades has fundamentally altered soil Fe oxides, potentially altering the bioavailability and retention of macro- and micronutrients, contaminants, and organic matter itself. The wide range of responses among the ecosystem's trace elements illustrates the great dynamics of the soil system over time scales of decades.Item Open Access Global desertification: Building a science for dryland development(Science, 2007-05) REYNOLDS; James, F; Smith, DM Stafford; Lambin, EF; Turner, BL; II; Mortimore, M; Batterbury, SPJ; Downing, TE; Dowlatabadi, H; Fernández, RJ; Herrick, JE; Huber-Sannwald, E; Leemans, R; Lynam, T; Maestre, FT; Ayarza, M; Walker, BIn this millennium, global drylands face a myriad of problems that present tough research, management, and policy challenges. Recent advances in dryland development, however, together with the integrative approaches of global change and sustainability science, suggest that concerns about land degradation, poverty, safeguarding biodiversity, and protecting the culture of 2.5 billion people can be confronted with renewed optimism. We review recent lessons about the functioning of dryland ecosystems and the livelihood systems of their human residents and introduce a new synthetic framework, the Drylands Development Paradigm (DDP). The DDP, supported by a growing and well-documented set of tools for policy and management action, helps navigate the inherent complexity of desertification and dryland development, identifying and synthesizing those factors important to research, management, and policy communities.Item Open Access Hydraulic redistribution of soil water by roots affects whole-stand evapotranspiration and net ecosystem carbon exchange.(New Phytol, 2010-07) Domec, Jean-Christophe; King, John S; Noormets, Asko; Treasure, Emrys; Gavazzi, Michael J; Sun, Ge; McNulty, Steven G*Hydraulic redistribution (HR) of water via roots from moist to drier portions of the soil occurs in many ecosystems, potentially influencing both water use and carbon assimilation. *By measuring soil water content, sap flow and eddy covariance, we investigated the temporal variability of HR in a loblolly pine (Pinus taeda) plantation during months of normal and below-normal precipitation, and examined its effects on tree transpiration, ecosystem water use and carbon exchange. *The occurrence of HR was explained by courses of reverse flow through roots. As the drought progressed, HR maintained soil moisture above 0.15 cm(3) cm(-3) and increased transpiration by 30-50%. HR accounted for 15-25% of measured total site water depletion seasonally, peaking at 1.05 mm d(-1). The understory species depended on water redistributed by the deep-rooted overstory pine trees for their early summer water supply. Modeling carbon flux showed that in the absence of HR, gross ecosystem productivity and net ecosystem exchange could be reduced by 750 and 400 g C m(-2) yr(-1), respectively. *Hydraulic redistribution mitigated the effects of soil drying on understory and stand evapotranspiration and had important implications for net primary productivity by maintaining this whole ecosystem as a carbon sink.Item Open Access Legacies of Lead Paint Contamination in the Mineral Soils Adjacent to Historic Buildings(2023-04-28)For hundreds of years, compounds containing the element lead (Pb) have been added to paint in order to improve the texture and weather resistance. Across the United States, millions of homes and buildings were painted with lead-based paints up through the 1970s, when lead paint was phased out following medical research confirming the link between lead and a variety of neurological and developmental disorders. Over 170 million Americans are estimated to have been exposed to lead levels above safe concentrations, many of whom were likely exposed to soil lead while playing in yards as children. Although the phase-out of lead in paint began over 50 years ago, the legacies of contamination from lead paint are still present in the soil in a meaningful way. This is largely due to the immobile nature of lead in the soil, tightly binding to clays and other particles, preventing it from being leached out of the soil. Previous soil lead studies have attempted to characterize spatial patterns of contamination at various scales, but this study is unique in the highly fine-scale sampling design around each structure. Up to 190 samples were taken around each structure, at a point density of 1 sample every 4-12 square meters, prioritizing areas closer to the base of the structure. Nine study sites were chosen in the vicinity of Durham, North Carolina, including 2 buildings that continue to be well-maintained, 5 dilapidated structures, and 2 footprints of buildings burned to the ground. For our study, we surveyed the top inch of the mineral soil using an Olympus Vanta portable X-ray Fluorescence Machine to get lead concentration in parts per million. At all nine of our study sites, we found evidence of elevated lead levels in the mineral soil that can reasonably be attributed to legacies of paint contamination. Sites varied in the intensity of lead contamination, ranging from maximum values below 300ppm to multiple samples above 5000ppm, and each had its own unique footprint of soil lead. Interpolations of lead concentration were created in ArcGIS from the point data. Despite the variation, we were able to draw a variety of conclusions about the state of soil lead around historic structures: • Concentrations are typically highest adjacent to the base of the structure, and often decline rapidly with distance. • Concentrations often decline back down to the geologic background within 4-12 meters of the structure, related to the maximum concentration. • The corners of buildings are often hotspots for lead contamination, likely due to weathering patterns of paint. • Topography and erosion of soil can affect concentrations and directionality of elevated lead plumes. • We did not find any direct pattern between lead levels and a building’s height, age, location, or level of maintenance. • Destroyed/burned structures can show very high hotspots even within the footprint of the former structure. • Mulch and other ground covers may either protect the soil from contamination or insulate the soil lead from loss. Statistical and geospatial analysis was used to help characterize the spatial patterns of the contamination at each site. For each structure, data of lead concentration versus distance from the building was used to generate a logarithmic regression that can be used to predict concentration at any given distance. For two structures, interpolations were georeferenced to estimate the area of spatial contamination at different thresholds. Other analyses were done on a site-specific basis, such as comparing concentrations at the different cardinal directions from one structure. All of our results were communicated and interpreted to the landowners to help inform their knowledge of their properties. This is especially important considering most of our sites are open to the public, and multiple have outdoor programs for children. For each site, we estimated a total health risk, based on the levels of lead contamination and the potential for human exposure. Considering the levels still present in soils even after 50+ years, more research is needed into soil remediation methods, as the high values we found in soils demonstrate that lead still poses a considerable risk to humans.Item Open Access Legacies of Lead Paint Contamination in the Mineral Soils Adjacent to Historic Buildings(2023-04-28) Skinner, Adam; Lambert, CarsonFor hundreds of years, compounds containing the element lead (Pb) have been added to paint in order to improve the texture and weather resistance. Across the United States, millions of homes and buildings were painted with lead-based paints up through the 1970s, when lead paint was phased out following medical research confirming the link between lead and a variety of neurological and developmental disorders. Over 170 million Americans are estimated to have been exposed to lead levels above safe concentrations, many of whom were likely exposed to soil lead while playing in yards as children. Although the phase-out of lead in paint began over 50 years ago, the legacies of contamination from lead paint are still present in the soil in a meaningful way. This is largely due to the immobile nature of lead in the soil, tightly binding to clays and other particles, preventing it from being leached out of the soil. Previous soil lead studies have attempted to characterize spatial patterns of contamination at various scales, but this study is unique in the highly fine-scale sampling design around each structure. Up to 190 samples were taken around each structure, at a point density of 1 sample every 4-12 square meters, prioritizing areas closer to the base of the structure. Nine study sites were chosen in the vicinity of Durham, North Carolina, including 2 buildings that continue to be well-maintained, 5 dilapidated structures, and 2 footprints of buildings burned to the ground. For our study, we surveyed the top inch of the mineral soil using an Olympus Vanta portable X-ray Fluorescence Machine to get lead concentration in parts per million. At all nine of our study sites, we found evidence of elevated lead levels in the mineral soil that can reasonably be attributed to legacies of paint contamination. Sites varied in the intensity of lead contamination, ranging from maximum values below 300ppm to multiple samples above 5000ppm, and each had its own unique footprint of soil lead. Interpolations of lead concentration were created in ArcGIS from the point data. Despite the variation, we were able to draw a variety of conclusions about the state of soil lead around historic structures: • Concentrations are typically highest adjacent to the base of the structure, and often decline rapidly with distance. • Concentrations often decline back down to the geologic background within 4-12 meters of the structure, related to the maximum concentration. • The corners of buildings are often hotspots for lead contamination, likely due to weathering patterns of paint. • Topography and erosion of soil can affect concentrations and directionality of elevated lead plumes. • We did not find any direct pattern between lead levels and a building’s height, age, location, or level of maintenance. • Destroyed/burned structures can show very high hotspots even within the footprint of the former structure. • Mulch and other ground covers may either protect the soil from contamination or insulate the soil lead from loss. Statistical and geospatial analysis was used to help characterize the spatial patterns of the contamination at each site. For each structure, data of lead concentration versus distance from the building was used to generate a logarithmic regression that can be used to predict concentration at any given distance. For two structures, interpolations were georeferenced to estimate the area of spatial contamination at different thresholds. Other analyses were done on a site-specific basis, such as comparing concentrations at the different cardinal directions from one structure. All of our results were communicated and interpreted to the landowners to help inform their knowledge of their properties. This is especially important considering most of our sites are open to the public, and multiple have outdoor programs for children. For each site, we estimated a total health risk, based on the levels of lead contamination and the potential for human exposure. Considering the levels still present in soils even after 50+ years, more research is needed into soil remediation methods, as the high values we found in soils demonstrate that lead still poses a considerable risk to humans.Item Open Access Legacy Pb contamination in the soils of three Durham city parks: Do secondary forest organic horizons effectively blanket Pb in city park soils contaminated by historic waste incineration?(2022-12-16) Bihari, EnikoeLead (Pb) has historically been used in many products such as gasoline, paint, batteries, ceramics, pipes and plumbing, solders, and cosmetics, and Pb contamination from these materials and their waste streams is widespread around the world. Pb is a highly insoluble and persistent contaminant that accumulates in the environment, especially in urban soils; to this day, soil Pb concentrations remain high in many cities, posing a significant long-term public health and environmental risk. Some remediation options are available for Pb, with the most effective being removal and replacement of the contaminated soil. However, plants that can tolerate soil Pb may be effective at phytostabilization. In phytostabilization, soil Pb is immobilized both physically and chemically by the roots, while also being sequestered by new layers of organic matter and soil that accumulate on the surface. Throughout the early 1900s, the city of Durham, NC operated neighborhood municipal incinerators which combusted most of the city’s waste, including waste collected from homes, businesses, and public street cleaning. Around 1950, the four of the incinerator sites were closed and converted into public parks, with playgrounds, grass fields, picnic benches, sports facilities, and walking paths. These are now Walltown, East End, East Durham, and Lyon Parks. The parks currently contain streams and large areas of secondary forest cover, which have been largely unmanaged throughout the last century. From local newspaper articles, we have direct evidence for the disposal of incinerator refuse at these sites and other Durham parks. While historic news accounts describe the incinerator sites being covered with topsoil, until this study there has been no monitoring of the status of contaminant metals in the soils throughout the parks. We hypothesized that the surface soils of these parks had elevated Pb concentrations as the result of the parks’ history of incineration. Our primary objectives were to: 1. Measure total mineral surface soil Pb concentrations across three of Durham’s urban parks which were historically used for waste incineration (Walltown, East End, and East Durham Parks). 2. Assess whether secondary hardwood forests have accumulated organic horizons that were effective barriers to Pb-contaminated mineral soil below. We sampled mineral surface soil and organic horizon according to a stratified random sampling design, and the samples were measured for total Pb with an Olympus Vanta pXRF instrument. Data were analyzed using R and ArcGIS Pro, resulting in statistical models and spatial interpolations. Our main results were: 1. Mineral soil Pb concentrations across Walltown, East End, and East Durham Parks are elevated above both geologic background levels and several EPA hazard thresholds, especially in some highly-trafficked areas. 2. Hardwood forest organic horizons provide a blanket for highly Pb-contaminated mineral soil, but a significant amounts of surface soil Pb is mixed up into these O horizons. Thus, exposure risk is not eliminated and can remain quite high. Our results show that all three parks have total Pb in surface soils (0-2.5 cm) well above the geologic background (0-30 ppm), with many soils exceeding the US EPA’s hazard thresholds for gardening (100 ppm), residential play areas (400 ppm), and residential non-play areas (1200 ppm). For all three parks combined, mineral soil Pb ranged from 8 to 2342 ppm, with a mean of 201 ppm and a median of 93 ppm. A notable hotspot with extremely high Pb was mapped throughout the southeastern portion of East Durham Park north of East Main St., spanning a grassy field and part a secondary forest (Figure 12). Mineral soil Pb in this hotspot ranged from 694 to 2342 ppm. This is of particular concern because this field is adjacent to an apartment building, and residents appear to use this area to play, garden, and park their cars. Additionally, our study demonstrates that while hardwood O horizons provide a physical barrier to exposure for highly contaminated mineral soil, a significant amount of mineral soil Pb is mixed up into the O horizons. This relationship differed significantly between the upper O1/O2 and the lower O3 horizons. Pb concentration in the lower O3 horizon increased by 0.6 ppm for every 1 ppm increase in Pb increase in the mineral soil, with an adjusted R2 of 0.86. This means that the lower O3 horizon has about 60% of the Pb concentration of the mineral soil below. In contrast, Pb concentration in the upper O1/O2 horizon increased by 0.1 ppm for every 1 ppm increase in Pb increase in the mineral soil, with an adjusted R2 of 0.49. This means that the upper O1/O2 horizons have about 10% of the Pb concentration of the mineral soil below, Our results suggest limitations to phytostabilization as tool to reduce Pb exposure, particularly in hardwood forests where there is relatively rapid decomposition and bioturbation in the O horizons compared to many coniferous forests. Overall, the spatial distribution of soil Pb concentrations demonstrates the complicated land use history of these landscapes, pointing towards multiple sources of Pb inputs and outputs throughout the 20th century. Based on articles in historic newspapers from five cities across the USA, many municipalities may have public parks converted from historic waste incinerator sites; these sites may be contaminated with Pb and other metals that would have accumulated in ash and cinders, posing an exposure risk to residents who visit the parks.Item Open Access Legacy source of mercury in an urban stream-wetland ecosystem in central North Carolina, USA.(Chemosphere, 2015-11) Deonarine, Amrika; Hsu-Kim, Heileen; Zhang, Tong; Cai, Yong; Richardson, Curtis JIn the United States, aquatic mercury contamination originates from point and non-point sources to watersheds. Here, we studied the contribution of mercury in urban runoff derived from historically contaminated soils and the subsequent production of methylmercury in a stream-wetland complex (Durham, North Carolina), the receiving water of this runoff. Our results demonstrated that the mercury originated from the leachate of grass-covered athletic fields. A fraction of mercury in this soil existed as phenylmercury, suggesting that mercurial anti-fungal compounds were historically applied to this soil. Further downstream in the anaerobic sediments of the stream-wetland complex, a fraction (up to 9%) of mercury was converted to methylmercury, the bioaccumulative form of the metal. Importantly, the concentrations of total mercury and methylmercury were reduced to background levels within the stream-wetland complex. Overall, this work provides an example of a legacy source of mercury that should be considered in urban watershed models and watershed management.Item Open Access Long-term transformation and fate of manufactured ag nanoparticles in a simulated large scale freshwater emergent wetland.(Environ Sci Technol, 2012-07-03) Lowry, GV; Espinasse, BP; Badireddy, AR; Richardson, CJ; Reinsch, BC; Bryant, LD; Bone, AJ; Deonarine, A; Chae, S; Therezien, M; Colman, BP; Hsu Kim, H; Bernhardt, ES; Matson, CW; Wiesner, MRTransformations and long-term fate of engineered nanomaterials must be measured in realistic complex natural systems to accurately assess the risks that they may pose. Here, we determine the long-term behavior of poly(vinylpyrrolidone)-coated silver nanoparticles (AgNPs) in freshwater mesocosms simulating an emergent wetland environment. AgNPs were either applied to the water column or to the terrestrial soils. The distribution of silver among water, solids, and biota, and Ag speciation in soils and sediment was determined 18 months after dosing. Most (70 wt %) of the added Ag resided in the soils and sediments, and largely remained in the compartment in which they were dosed. However, some movement between soil and sediment was observed. Movement of AgNPs from terrestrial soils to sediments was more facile than from sediments to soils, suggesting that erosion and runoff is a potential pathway for AgNPs to enter waterways. The AgNPs in terrestrial soils were transformed to Ag(2)S (~52%), whereas AgNPs in the subaquatic sediment were present as Ag(2)S (55%) and Ag-sulfhydryl compounds (27%). Despite significant sulfidation of the AgNPs, a fraction of the added Ag resided in the terrestrial plant biomass (~3 wt % for the terrestrially dosed mesocosm), and relatively high body burdens of Ag (0.5-3.3 μg Ag/g wet weight) were found in mosquito fish and chironomids in both mesocosms. Thus, Ag from the NPs remained bioavailable even after partial sulfidation and when water column total Ag concentrations are low (<0.002 mg/L).Item Open Access Low-severity fire as a mechanism of organic matter protection in global peatlands: Thermal alteration slows decomposition.(Global change biology, 2020-07) Flanagan, Neal E; Wang, Hongjun; Winton, Scott; Richardson, Curtis JWorldwide, regularly recurring wildfires shape many peatland ecosystems to the extent that fire-adapted species often dominate plant communities, suggesting that wildfire is an integral part of peatland ecology rather than an anomaly. The most destructive blazes are smoldering fires that are usually initiated in periods of drought and can combust entire peatland carbon stores. However, peatland wildfires more typically occur as low-severity surface burns that arise in the dormant season when vegetation is desiccated, and soil moisture is high. In such low-severity fires, surface layers experience flash heating, but there is little loss of underlying peat to combustion. This study examines the potential importance of such processes in several peatlands that span a gradient from hemiboreal to tropical ecozones and experience a wide range of fire return intervals. We show that low-severity fires can increase the pool of stable soil carbon by thermally altering the chemistry of soil organic matter (SOM), thereby reducing rates of microbial respiration. Using X-ray photoelectron spectroscopy and Fourier transform infrared, we demonstrate that low-severity fires significantly increase the degree of carbon condensation and aromatization of SOM functional groups, particularly on the surface of peat aggregates. Laboratory incubations show lower CO2 emissions from peat subjected to low-severity fire and predict lower cumulative CO2 emissions from burned peat after 1-3 years. Also, low-severity fires reduce the temperature sensitivity (Q10 ) of peat, indicating that these fires can inhibit microbial access to SOM. The increased stability of thermally altered SOM may allow a greater proportion of organic matter to survive vertical migration into saturated and anaerobic zones of peatlands where environmental conditions physiochemically protect carbon stores from decomposition for thousands of years. Thus, across latitudes, low-severity fire is an overlooked factor influencing carbon cycling in peatlands, which is relevant to global carbon budgets as climate change alters fire regimes worldwide.Item Open Access Maple and hickory leaf litter fungal communities reflect pre-senescent leaf communities.(PeerJ, 2022-01) Liber, Julian A; Minier, Douglas H; Stouffer-Hopkins, Anna; Van Wyk, Judson; Longley, Reid; Bonito, GregoryFungal communities are known to contribute to the functioning of living plant microbiomes as well as to the decay of dead plant material and affect vital ecosystem services, such as pathogen resistance and nutrient cycling. Yet, factors that drive structure and function of phyllosphere mycobiomes and their fate in leaf litter are often ignored. We sought to determine the factors contributing to the composition of communities in temperate forest substrates, with culture-independent amplicon sequencing of fungal communities of pre-senescent leaf surfaces, internal tissues, leaf litter, underlying humus soil of co-occurring red maple (Acer rubrum) and shagbark hickory (Carya ovata). Paired samples were taken at five sites within a temperate forest in southern Michigan, USA. Fungal communities were differentiable based on substrate, host species, and site, as well as all two-way and three-way interactions of these variables. PERMANOVA analyses and co-occurrence of taxa indicate that soil communities are unique from both phyllosphere and leaf litter communities. Correspondence of endophyte, epiphyte, and litter communities suggests dispersal plays an important role in structuring fungal communities. Future work will be needed to assess how this dispersal changes microbial community functioning in these niches.Item Open Access Modifying the ‘pulse-reserve’ paradigm for deserts of North America: precipitation pulses, soil water and plant responses(Oecologia, 2004) REYNOLDS; James, F; Kemp, PR; Ogle, K; Fernández, RJThe 'pulse-reserve' conceptual model--arguably one of the most-cited paradigms in aridland ecology--depicts a simple, direct relationship between rainfall, which triggers pulses of plant growth, and reserves of carbon and energy. While the heuristics of 'pulses', 'triggers' and 'reserves' are intuitive and thus appealing, the value of the paradigm is limited, both as a conceptual model of how pulsed water inputs are translated into primary production and as a framework for developing quantitative models. To overcome these limitations, we propose a revision of the pulse-reserve model that emphasizes the following: (1) what explicitly constitutes a biologically significant 'rainfall pulse', (2) how do rainfall pulses translate into usable 'soil moisture pulses', and (3) how are soil moisture pulses differentially utilized by various plant functional types (FTs) in terms of growth? We explore these questions using the patch arid lands simulation (PALS) model for sites in the Mojave, Sonoran, and Chihuahuan deserts of North America. Our analyses indicate that rainfall variability is best understood in terms of sequences of rainfall events that produce biologically-significant 'pulses' of soil moisture recharge, as opposed to individual rain events. In the desert regions investigated, biologically significant pulses of soil moisture occur in either winter (October-March) or summer (July-September), as determined by the period of activity of the plant FTs. Nevertheless, it is difficult to make generalizations regarding specific growth responses to moisture pulses, because of the strong effects of and interactions between precipitation, antecedent soil moisture, and plant FT responses, all of which vary among deserts and seasons. Our results further suggest that, in most soil types and in most seasons, there is little separation of soil water with depth. Thus, coexistence of plant FTs in a single patch as examined in this PALS study is likely to be fostered by factors that promote: (1) separation of water use over time (seasonal differences in growth), (2) relative differences in the utilization of water in the upper soil layers, or (3) separation in the responses of plant FTs as a function of preceding conditions, i.e., the physiological and morphological readiness of the plant for water-uptake and growth. Finally, the high seasonal and annual variability in soil water recharge and plant growth, which result from the complex interactions that occur as a result of rainfall variability, antecedent soil moisture conditions, nutrient availability, and plant FT composition and cover, call into question the use of simplified vegetation models in forecasting potential impacts of climate change in the arid zones in North America.