Sites In Central Pennsylvania Research Articles

Spatiotemporal patterns of PFAS in water and crop tissue at a beneficial wastewater reuse site in central Pennsylvania.

Per- and polyfluoroalkyl substances (PFAS) are a collective name for thousands of synthetic compounds produced to enhance consumer and industrial products since the 1940s. They do not easily degrade, and some are known to pose serious ecological and human health concerns at trace concentrations (ng L-1 levels). Per- and polyfluoroalkyl substances persist in treated wastewater and are inadvertently introduced into the environment when treated wastewater is reused as an irrigation source. The Pennsylvania State University (PSU) has been spray-irrigating its wastewater at a 2.45 km2 mixed-use agricultural and forested site known as the "Living Filter" since the 1960s. To understand the spatiotemporal patterns of 20 PFAS at the Living Filter, water samples were collected bimonthly from fall 2019 through winter 2021 from the PSU's wastewater effluent and from each of the site's 13 monitoring wells. Crop tissue was collected at the time of harvest to assess PFAS presence in corn silage and tall fescue grown at the study site. Total measured PFAS concentrations in the monitoring wells ranged from nondectable to 155ng L-1 , with concentrations increasing with the direction of groundwater flow. Concentrations within each well exhibited little temporal variability across sampling events, with mixed relationships between PFAS and groundwater elevation observed between wells. Further, >84% of the PFAS present in livestock feed crops were short-chain compounds, with PFAS consumed annually by livestock fed crops harvested from the site estimated to be 2.46-7.67mg animal-1 yr-1 . This research provides insight into the potential impacts of long-term beneficial reuse of treated wastewater on groundwater and crop tissue quality.

Virtual field experiences in a web-based video game environment: open-ended examples of existing and fictional field sites

Abstract. We present two original, video-game-style field geology experiences designed to allow flexible, open-ended exploration for geologic mapping and structural geology. One simulation features the Whaleback anticline, a site in central Pennsylvania (USA), with a three-dimensional exposure of a 30 m high fold, based on a terrain model that was acquired through structure-from-motion photogrammetry. The second example is a fictional location with simplified geology, which was built with digital modeling software and inspired by the geology of northwestern Washington. Users move through the terrain, as if in the field, selecting where to make observations of the geologic structure. Additionally, these virtual field experiences provide novel visualization opportunities through tools like a geodetic compass that instantly plots data to a stereonet and a jetpack simulation, which allows the user to interrogate geologic surfaces in hard-to-reach locations. We designed the virtual field experiences in a widely used video-game-creation software and published the field simulations for access via the internet and common web browsers so that no special hardware or software is required to play. We implemented these field simulations to partially replace field and lab exercises in two different courses offered remotely through the University of Washington Department of Earth and Space Sciences, with assignments that address many of the learning goals of traditional in-person exercises. Because the virtual field experiences are open-ended, other instructors can design different exercises to meet different learning goals. While this game environment currently serves as an enhancement to remote education, this format can also augment traditional educational experiences, overcoming several challenges to accessing the field or particular outcrops and, thereby, broadening opportunities for participation and scientific collaboration.

A quantitative method for collecting water mites in lotic, riffle-run habitats for water quality biomonitoring

Previous research surrounding water mites has primarily focused on understanding taxonomy, distribution, and life history. For these purposes, qualitative sampling methods have been sufficient. However, there has been increasing interest among acarologists and aquatic entomologists in the ability of water mites to serve as bioindicators of water quality conditions. Therefore, scientists have acknowledged the need for a standardized, quantitative sampling scheme. Such a method is described herein as we provide a detailed description of how to collect water mites from lotic, riffle-run environments. In addition, we provide observations to how this method compares to regularly applied benthic macroinvertebrate collection methods in terms of physical demand and time commitment. To demonstrate its efficiency, this method was applied to 23 sites in central Pennsylvania, United States, where it successfully collected more than 8,000 individual water mites.

Phylogenetic Signal, Root Morphology, Mycorrhizal Type, and Macroinvertebrate Exclusion: Exploring Wood Decomposition in Soils Conditioned by 13 Temperate Tree Species.

Woodlands are pivotal to carbon stocks, but the process of cycling C is slow and may be most effective in the biodiverse root zone. How the root zone impacts plants has been widely examined over the past few decades, but the role of the root zone in decomposition is understudied. Here, we examined how mycorrhizal association and macroinvertebrate activity influences wood decomposition across diverse tree species. Within the root zone of six predominantly arbuscular mycorrhizal (AM) (Acer negundo, Acer saccharum, Prunus serotina, Juglans nigra, Sassafras albidum, and Liriodendron tulipfera) and seven predominantly ectomycorrhizal (EM) tree species (Carya glabra, Quercus alba, Quercus rubra, Betula alleghaniensis, Picea rubens, Pinus virginiana, and Pinus strobus), woody litter was buried for 13 months. Macroinvertebrate access to woody substrate was either prevented or not using 0.22 mm mesh in a common garden site in central Pennsylvania. Decomposition was assessed as proportionate mass loss, as explained by root diameter, phylogenetic signal, mycorrhizal type, canopy tree trait, or macroinvertebrate exclusion. Macroinvertebrate exclusion significantly increased wood decomposition by 5.9%, while mycorrhizal type did not affect wood decomposition, nor did canopy traits (i.e., broad leaves versus pine needles). Interestingly, there was a phylogenetic signal for wood decomposition. Local indicators for phylogenetic associations (LIPA) determined high values of sensitivity value in Pinus and Picea genera, while Carya, Juglans, Betula, and Prunus yielded low values of sensitivity. Phylogenetic signals went undetected for tree root morphology. Despite this, roots greater than 0.35 mm significantly increased woody litter decomposition by 8%. In conclusion, the findings of this study suggest trees with larger root diameters can accelerate C cycling, as can trees associated with certain phylogenetic clades. In addition, root zone macroinvertebrates can potentially limit woody C cycling, while mycorrhizal type does not play a significant role.

Matching a snail's pace: successful use of environmental DNA techniques to detect early stages of invasion by the destructive New Zealand mud snail.

Early detection of invasive species allows for a more rapid and effective response. Restoration of the native ecosystem after an invasive population has established is expensive and difficult but more likely to succeed when invasions are detected early in the invasion process. Containment efforts to prevent the spread of known invasions also benefit from earlier knowledge of invaded sites. Environmental DNA (eDNA) techniques have emerged as a tool that can identify invasive species at a distinctly earlier time point than traditional methods of detection. Here, we focus on whether eDNA techniques can be successfully applied to detect new invasions by the destructive New Zealand Mud Snail Potamopyrgus antipodarum (NZMS). It is an opportune time to apply eDNA-based detection in P. antipodarum, which is currently expanding its invasive range across eastern North America. We collected water samples from eight sites in central Pennsylvania that prior evidence indicated were not yet invaded by the NZMS but were part of the same watershed as other previously documented invaded sites. We found evidence for NZMS invasion at five of the eight sites, with subsequent physical confirmation of mud snails at one of these sites. This study is the first example of successful application of eDNA to detect a previously unidentified invasive population of NZMS, setting the stage for further monitoring of at-risk sites to detect and control new invasions of this destructive snail. This study also shows potential opportunities for invasion monitoring offered by using low-cost efforts and methods that are adaptable for citizen science.

The impacts of Marcellus Shale gas drilling accidents on amphibians in a Pennsylvania fen

Gas drilling into the Marcellus Shale play has been linked to environmental issues, including potential impacts on wildlife. In 2009, three separate accidents occurred at two gas well sites in central Pennsylvania, USA that resulted in high levels of contaminants in Wallace Mine Fen and a headwater stream that flows through the fen. We collected water chemistry, vegetation, and amphibian data at the impacted fen and at a control fen in 2012 and 2013 to determine similarity of sites and the impacts of the contaminants. We also reviewed water chemistry reports generated by the Pennsylvania Department of Environmental Protection for data collected shortly after the accidents occurred to provide insight on the nature of the accidents. Ordinations of vegetation data, as well as water chemistry, showed that the two wetlands are similar and dominated by the same plant species and water chemistry. Historically, both wetlands provided habitat for amphibians. However, unlike in pre-accident amphibian data, we detected virtually no amphibians in the impacted Wallace Mine Fen, suggesting that amphibians were possibly negatively affected by gas-drilling accidents.

Evaluation of Fe isotope values as a provenance tool for chert artefacts from the north‐eastern United States

Iron (Fe) isotope compositions of prehistoric stone tools and geological sources were compared to evaluate the robustness of this isotopic fingerprinting technique. Artefacts and source materials were collected from the Hatch site in central Pennsylvania, United States, where both veined chert (Bald Eagle chert) and stone tools coexist within several metres. Yellow artefacts (δ56Fe = 0.38 ± 0.1, n = 7) and source materials (δ56Fe = 0.42 ± 0.1, n = 8) isotopically matched within error. The source values also overlap yellow chert samples from three other Bald Eagle chert locations in the area. These values are different from six other chert locations in the north‐eastern United States. These data suggest that the Fe isotope composition of chert artefacts reflect distinct geological sources. To enhance the mechanical characteristics of the stone tools, the chert experienced heat treatment, which induced a phase shift of the Fe oxide mineral goethite to hematite. This phase shift changes the colour of the chert to red. The red chert artefacts and source material also have overlapping Fe isotope values, but are 0.2‰ higher than the initial yellow chert. Experimental work where cherts were heated with different clays shows that Fe exchange with site soils induces the +0.2 fractionation. These data demonstrate that predictable Fe isotope fractionation occurs during heating, resulting in isotopically distinct artefacts.

Plant identity, but not diversity, and agroecosystem characteristics affect the occurrence of M. robertsii in an organic cropping system

Organic farmers rely largely on cultural practices, such as crop rotation and cover cropping, and on biological control to manage pests. Winter cover crops add diversity to agroecosystems and can benefit soil conservation and health, retention and supply of soil nutrients, regulation of arthropods, and crop yields. Within the framework of a three-year experiment to investigate ecosystem services and disservices associated with 12 winter cover crop treatments during the transition of a small grain – corn – soybean production system to organic management, we examined the effects of cash crop and crop management, cover crop species and diversity, arthropods, and soil properties on Metarhizium spp. in a single field site in central Pennsylvania, USA. We used sentinel insect assays with Galleria mellonella L. to determine the relative occurrence of Metarhizium spp. in soil samples from treatment plots. M. robertsii was the only species detected, and therefore Metarhizium species diversity was not related to cover crop diversity. Detection of M. robertsii was lower in cover crop monocultures and mixtures containing brassicas compared to those with legumes. M. robertsii was detected more frequently in the standing cover crops in the corn phase of the rotation than in the soybean phase, but there was no difference in soil samples in the corn and soybeans after cover crop termination. In samples from cover crops, 33% of the variation of percentage mortality of sentinel G. mellonella by M. robertsii was explained by positive correlations with cover crop biomass in the previous fall, the biomass of weeds in the current season (spring), soil moisture, Ca, and timing of sampling in days after planting, and by negative correlations with number of days since disturbance prior to soil sampling and percent sand. In samples from corn and soybeans, 23% of the variation of percentage mortality of sentinel G. mellonella by M. robertsii was explained by positive correlations with soil labile C, electrical conductivity, and activity-density of ground beetles (Carabidae), and by negative correlations with increasing number of days after planting relative to time of sampling, percent sand, and activity-density of mites. The complex interactions of multiple biotic and abiotic factors that shape the soil community requires further research to develop an understanding of how to manage production systems and practices to promote and conserve biological control in the soil.

Understanding the implementation of the Grow! parenting program: Findings from a mixed methods pilot study

Evaluating the implementation of parenting interventions is critical to program diffusion and quality across populations and settings, and to enhancing treatment outcomes. This article presents implementation findings from a pilot study of Grow!, a universal parenting program targeting parents of five to eight years olds that aims to improve child outcomes through strengthened parenting. Grow! was implemented at two community sites in central Pennsylvania by trained facilitators. Implementation data was gathered from facilitators and participants using mixed methods, including surveys, observation checklists, semi-structured interviews, and focus group discussions. These data were analyzed and integrated to explore, within the context of Proctor et al.'s (2011) implementation outcome framework, four implementation outcomes (i.e., acceptability, appropriateness, fidelity, and feasibility). Overall, these findings demonstrate that Grow! can be, and was, implemented effectively in a community setting. Moreover, they demonstrate how the Proctor et al. (2011) framework can be operationalized and applied specifically to hybrid effectiveness-implementation design studies.

Radiation fog chemical composition and its temporal trend over an eight year period

Radiation fog samples have been collected at a rural site in Central Pennsylvania from 2007 through 2015 in order to document chemical composition, assess concentration changes over time, and to provide insight into emission sources that influence the region. The collection of samples over multiple years makes this one of the few long duration radiation fog studies that have been completed. During the course of the campaign, 146 samples were obtained and analyzed for pH, major inorganic ions, low molecular weight organic acids, total organic carbon (TOC) and total nitrogen (TN). Ammonium (median concentration = 209 μN), sulfate (69 μN), calcium (51 μN), and nitrate (31 μN) were the most abundant inorganic ions, although these were present at much lower concentrations than for radiation fog studies conducted in other locations. Organic acids, of which formate (20 μM) and acetate (21 μM) were the most abundant, were closer in magnitude to measurements made during previous studies. Organic acids accounted for 15% of TOC, which had a median concentration of 6.6 mgC l−1. The median concentration of TN was 3.6 mgN l−1, 18% of which was determined to be organic nitrogen. Statistically significant decreasing trends from 2007 to 2015 were noted for sulfate, ammonium, chloride, and nitrate. For the same period, an increase in pH was observed. Seasonal trends were identified for a number of species as well. The partitioning of ammonia between the gas and aqueous phases was also investigated and found to deviate significantly from equilibrium.

Plant community associations of two invasive thistles.

In order to combat the growing problems associated with biological invasions, many researchers have focused on identifying which communities are most vulnerable to invasion by exotic species. However, once established, invasive species can significantly change the composition of the communities that they invade. The first step to disentangling the direction of causality is to discern whether a relationship with other vegetation exists at all. Carduus nutans and C. acanthoides are similar invasive thistles, which have caused substantial economic damage worldwide. We assessed the associations between the thistles and the standing flora in four sites in central Pennsylvania in which they co-occur. After sampling nearly 2000 plots of 1 m(2), we used partial Mantel tests to assess the differences in vegetation between thistle and non-thistle plots after accounting for location, and non-metric multidimensional scaling to visualize differences among plots and sites. We found significant differences in community composition in plots with and without Carduus thistles. The non-native species Sisymbrium officinale and Coronilla varia were consistently associated with the presence of Carduus thistles. Several species were associated with areas that were free of Carduus thistles, including an important non-native pasture species (Trifolium repens). We found no evidence for differences in composition between plots with C. nutans versus C. acanthoides, suggesting that they have similar associations with the vegetation community. We conclude that even at the within-field scale, areas invaded by Carduus thistles have different vegetation associations than uninvaded areas, allowing us to target future research about the role of vegetation structure in resisting and responding to invasion.

Living with Aliens: Effects of Invasive Shrub Honeysuckles on Avian Nesting

Invasive species have come to the forefront of conservation biology as a major threat to native biodiversity. Habitats dominated by shrub honeysuckles (Lonicera spp.) in the United States have been characterized as “ecological traps” by ecologists. Here we tested this hypothesis by investigating the effects of shrub honeysuckles on the nesting ecology of native birds in seven study sites in central Pennsylvania, USA. We examined how the abundance of shrub honeysuckles influenced the selection of nesting substrates and habitat for a community of common songbirds, and the parental-care behavior and nestling development of gray catbirds (Dumetella carolinensis). We found that birds had a strong bias towards nesting in honeysuckle shrubs, but not necessarily for nesting in honeysuckle-dominated habitats. Nest predation rates were affected by the density of nests in a habitat, but not by the overall abundance of honeysuckles in such habitats. Honeysuckle abundance in the habitat did show significant effects on some parental-care behavioral parameters: catbirds had higher nest visitation rates and shorter visit lengths in areas of high honeysuckle density. On average, Gray catbirds fed fruit 12%±0.31 s.e. of their nestling-feeding bouts, mostly fruits of shrub honeysuckles. Nestlings in sites with high honeysuckle density also showed higher mass:tarsus ratios, suggesting a good (possibly better) physiological condition of catbird nestlings at the time of fledging. Our study shows that honeysuckle-dominated habitats could have equivocal effects on nesting parameters of common species of native birds. We advise more caution in the widespread denomination of novel plant communities with high densities of honeysuckle as “ecological traps” as effects can be null or positive on native birds in certain localities.

An integral-balance nonlinear model to simulate changes in soil moisture, groundwater and surface runoff dynamics at the hillslope scale

We present a system of ordinary differential equations (ODEs) capable of reproducing simultaneously the aggregated behavior of changes in water storage in the hillslope surface, the unsaturated and the saturated soil layers and the channel that drains the hillslope. The system of equations can be viewed as a two-state integral-balance model for soil moisture and groundwater dynamics. Development of the model was motivated by the need for landscape representation through hillslopes and channels organized following stream drainage network topology. Such a representation, with the basic discretization unit of a hillslope, allows ODEs-based simulation of the water transport in a basin. This, in turn, admits the use of highly efficient numerical solvers that enable space–time scaling studies. The goal of this paper is to investigate whether a nonlinear ODE system can effectively replicate observations of water storage in the unsaturated and saturated layers of the soil. Our first finding is that a previously proposed ODE hillslope model, based on readily available data, is capable of reproducing streamflow fluctuations but fails to reproduce the interactions between the surface and subsurface components at the hillslope scale. However, the more complex ODE model that we present in this paper achieves this goal. In our model, fluxes in the soil are described using a Taylor expansion of the underlying storage flux relationship. We tested the model using data collected in the Shale Hills watershed, a 7.9-ha forested site in central Pennsylvania, during an artificial drainage experiment in August 1974 where soil moisture in the unsaturated zone, groundwater dynamics and surface runoff were monitored. The ODE model can be used as an alternative to spatially explicit hillslope models, based on systems of partial differential equations, which require more computational power to resolve fluxes at the hillslope scale. Therefore, it is appropriate to be coupled to runoff routing models to investigate the effect of runoff and its uncertainty propagation across scales. However, this improved performance comes at the expense of introducing two additional parameters that have no obvious physical interpretation. We discuss the implications of this for hydrologic studies across scales.

Impact of Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) on outbreak gypsy moth populations (Lepidoptera: Erebidae): the role of weather.

The fungal pathogen Entomophaga maimaiga Humber, Shimazu, and Soper is prevalent in gypsy moth [Lymantria dispar (L.)] populations throughout North America. To understand how weather-related variables influence gypsy moth-E. maimaiga interactions in the field, we measured fungal infection rates at 12 sites in central Pennsylvania over 3 yr, concurrently measuring rainfall, soil moisture, humidity, and temperature. Fungal mortality was assessed using both field-collected larvae and laboratory-reared larvae caged on the forest floor. We found significant positive effects of moisture-related variables (rainfall, soil moisture, and relative humidity) on mortality due to fungal infection in both data sets, and significant negative effects of temperature on the mortality of field-collected larvae. Lack of a clear temperature relationship with the mortality of caged larvae may be attributable to differential initiation of infection by resting spores and conidia or to microclimate effects. These relationships may be helpful in understanding how gypsy moth dynamics vary across space and time, and in forecasting how the gypsy moth and fungus will interact as they move into warmer or drier areas, or new weather conditions occur due to climate change.

Turnover of Soil Carbon following Addition of Switchgrass-Derived Biochar to Four Soils

Amending soils with biochar can sequester C and improve soil properties, such as nutrient holding capacity and water retention. While biochars generally have a long residence time in soil, the turnover of biochar C can be influenced by both biochar characteristics and soil properties. Biochar can also potentially alter the rate of decomposition of native soil organic matter (SOM). The turnover of switchgrass (Panicum virgatum L.)-derived biochar C was evaluated in the laboratory using soil from four marginally productive sites in central Pennsylvania. Carbon dioxide emissions from unamended soil, biochar-amended soil, and pure biochar were monitored during 189-d incubations, and data were fit to a two-pool exponential model to estimate the amount and mean residence time (MRT) of C in labile and stable pools. Carbon-13 signatures of emitted CO₂ were also determined to estimate the proportion of emitted CO₂ derived from the biochar. Mixing biochar with each of the soils reduced the apparent MRT of C in both labile and stable pools, but the magnitude of change depended on the soil. Overall, the biochar was largely stable in each soil, with only 1.1 to 2.1% of the added biochar C emitted during incubation. There was no measurable effect of biochar amendment on the turnover of native SOM in any of the soils. Therefore, we conclude that amendment of our soils with switchgrass-derived biochar can effectively increase net C sequestration.

Schwertmannite and Fe oxides formed by biological low-pH Fe(II) oxidation versus abiotic neutralization: Impact on trace metal sequestration

Three low-pH coal mine drainage (CMD) sites in central Pennsylvania were studied to determine similarities in sediment composition, mineralogy, and morphology. Water from one site was used in discontinuous titration/neutralization experiments to produce Fe(III) minerals by abiotic oxidative hydrolysis for comparison with the field precipitates that were produced by biological low-pH Fe(II) oxidation. Even though the hydrology and concentration of dissolved metals of the CMD varied considerably between the three field sites, the mineralogy of the three iron mounds was very similar. Schwertmannite was the predominant mineral precipitated at low-pH (2.5–4.0) along with lesser amounts of goethite. Trace metals such as Zn, Ni and Co were only detected at μmol/g concentrations in the field sediments, and no metals (other than Fe) were removed from the CMD at any of the field sites. Metal cations were not lost from solution in the field because of unfavorable electrostatic attraction to the iron mound minerals. Ferrihydrite was the predominant mineral formed by abiotic neutralization (pH 4.4–8.4, 4 d aging) with lesser amounts of schwertmannite and goethite. In contrast to low-pH precipitation, substantial metal removal occurred in the neutralized CMD. Al was likely removed as hydrobasaluminite and Al(OH) 3, and as a co-precipitate into schwertmannite or ferrihydrite. Zn, Ni and Co were likely removed via adsorption onto and co-precipitation into the freshly formed Fe and Al solids. Mn was likely removed by co-precipitation and, at the highest final pH values, as a Mn oxide. Biological low-pH Fe(II) oxidation can be cost-effectively used to pre-treat CMD and remove Fe and acidity prior to conventional neutralization techniques. A further benefit is that solids formed under these conditions may be of industrial value because they do not contain trace metal or metalloid contaminants.

Soil Calcium Availability Limits Forest Songbird Productivity and Density

ABSTRACT. Forest soils in many areas of the world are becoming increasingly acidified, in part because of atmospheric deposition of strong acids produced by the burning of fossil fuels. Soil acidification and subsequent calcium depletion of forest soils in eastern North America have the potential to affect forest songbird populations negatively by reducing the availability of calcium-rich food items that are critical for reproduction. Nonetheless, little experimental evidence exists for the purported relationship between soil calcium and avian reproduction. Our objective was to use an experimental and observational study to determine how forest songbird-habitat quality is related to soil calcium availability. We experimentally elevated soil calcium using limestone sand and observed a 1.8-fold increase in Ovenbird (Seiurus aurocapilla) territory density, larger clutch sizes and more nests, but no effects on egg characteristics. The observational study of 14 forested sites in central Pennsylvania likewise s...

Using atmospheric chemistry and storm track information to explain the variation of nitrate stable isotopes in precipitation at a site in central Pennsylvania, USA

Stable isotopes of NO 3 − ( δ 15N–NO 3 − and δ 18O–NO 3 −) were monitored in precipitation at a central Pennsylvania site during six storm events in 2005 to determine whether information on atmospheric oxidants (e.g., O 3, NO 2, and NO x), and storm tracks (using the NOAA HYSPLIT model) were capable of explaining observed seasonal and within-storm isotopic variation. Results showed that δ 15N–NO 3 − and δ 18O–NO 3 − in precipitation varied significantly during individual storm events. Seasonally, δ 15N–NO 3 − and δ 18O–NO 3 − in precipitation followed a pattern of depletion during the summer months and enrichment during the winter months. NO 3 − precursor concentrations and atmospheric oxidants were useful for explaining the seasonal and within-storm variation of δ 15N–NO 3 − for all six storm events as evidenced by negative relationships with NO 2:NO x ratios and ozone (O 3). In comparison, δ 18O–NO 3 − was positively related to O 3 in three dormant season storms, which suggested that the O 3 oxidation pathway was important for producing the high δ 18O–NO 3 − observed in wintertime precipitation. Storm track information was especially useful for describing differences in δ 15N–NO 3 −. Cool-sector storms originating from the E/NE produced slightly negative δ 15N–NO 3 − values characteristic of automobile emissions, whereas warm-sector storms with tracks from the SW/S/SE produced slightly positive δ 15N–NO 3 − values characteristic of coal-fired emissions. Lightning also may have been an important source of atmospheric NO 3 − during two warm-sector thunderstorms. This study showed that (1) information about oxidant levels can be useful to predict the seasonal and within-storm variation of NO 3 − stable isotopes in precipitation, and (2) knowledge of storm tracks (warm-sector versus cool-sector) may be important for determining sources of NO 3 − in wet deposition.

Hydroxyl and Peroxy Radical Chemistry in a Rural Area of Central Pennsylvania: Observations and Model Comparisons

Atmospheric hydroxyl (OH), hydroperoxy (HO2), total peroxy (HO2 and organic peroxy radicals, RO2) mixing ratios and OH reactivity (first order OH loss rate) were measured at a rural site in central Pennsylvania during May and June 2002. OH and HO2 mixing ratios were measured with laser induced fluorescence (LIF); HO2 + RO2 mixing ratios were measured with chemical ionization mass spectrometry (CIMS). The daytime maximum mixing ratios were up to 0.6 parts per trillion by volume (pptv) for OH, 30 pptv for HO2, and 45 pptv for HO2 + RO2. A parameterized RACM (Regional Atmospheric Chemistry Mechanism) box model was used to predict steady state OH, HO2 and HO2 + RO2 concentrations by constraining the model to the measured OH reactivity and previously measured volatile organic compound (VOC) distributions. The averaged model calculations are generally in good agreement with the observations. For OH, the model matched the observations for day and night, with an average observed-to-modeled ratio of 0.80. In previous studies such as PROPHET98, nighttime NO was near 0 pptv and observed nighttime OH was significantly larger than modeled OH. In this study, nighttime observed and modeled OH agree to within measurement and model uncertainties because the main source of the nighttime OH was the reaction HO2 + NO → OH + NO2, with the NO being continually emitted from the surrounding fertilized corn field. The observed-to-modeled ratio for HO2 is 1.0 on average, although daytime HO2 is underpredicted by a factor of 1.2 and nighttime HO2 is over-predicted by a factor of ∼2. The average measured and modeled HO2 + RO2 agree well during daytime, but the modeled value is about twice the measured value during nighttime. While measured HO2 + RO2 values agree with modeled values for NO mixing ratios less than a few parts per billion by volume (ppbv), it increases substantially above the expected value for NO greater than a few ppbv. This observation of the higher-than-expected HO2 + RO2 with the CIMS technique confirms the observed increase of HO2 above expected values at higher NO mixing ratios in HO2 measurements with the LIF technique. The maximum instantaneous O3 production rate calculated from HO2 and RO2 reactions with NO was as high as 10–15 ppb h−1 at midday; the total daily O3 production varied from 13 to 113 ppbv d−1 and was 48 ppbv d−1 on average during this campaign.

Nest-searching cues and studies of nest-site selection and nesting success

Locating and monitoring nests are among the most widely used approaches in studies of avian ecology, evolution, and conservation. While several papers outline “best practices” for nest studies, nest-searching techniques are seldom standardized in field investigations because observers generally use strategies that work best for them. In this study, I examined if field observers differed in the cues they used to locate nests, the species they found, and the fate of their nests (i.e., successful or failed), and the extent to which nest-searching cues were associated with either nest fate or vegetation characteristics surrounding the nest. My field assistants and I monitored 355 songbird nests on 10 forested sites in central Pennsylvania in 1998–99. Parental behavior was the most frequently used cue for locating nests (41%), followed by systematic searching of nesting substrate (37%). Accidental flushing of the parent (5%) and luck (17%) were involved in fewer located nests. Field observers differed in the cues they used to find nests, and these nest-searching cues were associated with finding certain species. In addition, estimates of nesting success (percentage of nests fledging young) differed among field observers by up to 2.35×. Nest-searching cues were related to nest-placement (e.g., nest height) and vegetation characteristics (e.g., leaf litter) within nest-patches for Ovenbirds (Seiurus aurocapillus), Red-eyed Vireos (Vireo olivaceus), and Scarlet Tanagers (Piranga olivacea), although cues were not significantly related to the fate of nests. Overall, nest-searching cues were associated with nest placement, nest-patch habitat, and species composition of nest samples, all of which can ultimately influence findings from nesting studies. Consequently, investigators should exercise caution when allocating individual effort across experimental units and consider assigning each observer to ≥1 treatment, multiple observers to each site, and addressing nest-patch and nest-placement differences among cues through training and data analysis.