VTechWorks Repository :: Browsing by Author "Steele, Meredith K."

Browsing by Author "Steele, Meredith K."

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Climate and lawn management interact to control C-4 plant distribution in residential lawns across seven US cities
Trammell, Tara L. E.; Pataki, Diane E.; Still, Christopher J.; Ehleringer, James R.; Avolio, Meghan L.; Bettez, Neil; Cavender-Bares, Jeannine; Groffman, Peter M.; Grove, J. Morgan; Hall, Sharon J.; Heffernan, James B.; Hobbie, Sarah E.; Larson, Kelli L.; Morse, Jennifer L.; Neill, Christopher; Nelson, Kristen C.; O'Neil-Dunne, Jarlath P.M.; Pearse, William D.; Chowdhury, Rinku Roy; Steele, Meredith K.; Wheeler, Megan M. (2019-06)
In natural grasslands, C-4 plant dominance increases with growing season temperatures and reflects distinct differences in plant growth rates and water use efficiencies of C-3 vs. C-4 photosynthetic pathways. However, in lawns, management decisions influence interactions between planted turfgrass and weed species, leading to some uncertainty about the degree of human vs. climatic controls on lawn species distributions. We measured herbaceous plant carbon isotope ratios (delta C-13, index of C-3/C-4 relative abundance) and C-4 cover in residential lawns across seven U.S. cities to determine how climate, lawn plant management, or interactions between climate and plant management influenced C-4 lawn cover. We also calculated theoretical C-4 carbon gain predicted by a plant physiological model as an index of expected C-4 cover due to growing season climatic conditions in each city. Contrary to theoretical predictions, plant delta C-13 and C-4 cover in urban lawns were more strongly related to mean annual temperature than to growing season temperature. Wintertime temperatures influenced the distribution of C-4 lawn turf plants, contrary to natural ecosystems where growing season temperatures primarily drive C-4 distributions. C-4 cover in lawns was greatest in the three warmest cities, due to an interaction between climate and homeowner plant management (e.g., planting C-4 turf species) in these cities. The proportion of C-4 lawn species was similar to the proportion of C-4 species in the regional grass flora. However, the majority of C-4 species were nonnative turf grasses, and not of regional origin. While temperature was a strong control on lawn species composition across the United States, cities differed as to whether these patterns were driven by cultivated lawn grasses vs. weedy species. In some cities, biotic interactions with weedy plants appeared to dominate, while in other cities, C-4 plants were predominantly imported and cultivated. Elevated CO2 and temperature in cities can influence C-3/C-4 competitive outcomes; however, this study provides evidence that climate and plant management dynamics influence biogeography and ecology of C-3/C-4 plants in lawns. Their differing water and nutrient use efficiency may have substantial impacts on carbon, water, energy, and nutrient budgets across cities.
Continental-scale homogenization of residential lawn plant communities
Wheeler, Megan M.; Neill, Christopher; Groffman, Peter M.; Avolio, Meghan L.; Bettez, Neil; Cavender-Bares, Jeannine; Chowdhury, Rinku Roy; Darling, Lindsay E.; Grove, J. Morgan; Hall, Sharon J.; Heffernan, James B.; Hobbie, Sarah E.; Larson, Kelli L.; Morse, Jennifer L.; Nelson, Kristen C.; Ogden, Laura A.; O'Neil-Dunne, Jarlath P.M.; Pataki, Diane E.; Polsky, Colin; Steele, Meredith K.; Trammell, Tara L. E. (2017-09)
Residential lawns are highly managed ecosystems that occur in urbanized landscapes across the United States. Because they are ubiquitous, lawns are good systems in which to study the potential homogenizing effects of urban land use and management together with the continental-scale effects of climate on ecosystem structure and functioning. We hypothesized that similar homeowner preferences and management in residential areas across the United States would lead to low plant species diversity in lawns and relatively homogeneous vegetation across broad geographical regions. We also hypothesized that lawn plant species richness would increase with regional temperature and precipitation due to the presence of spontaneous, weedy vegetation, but would decrease with household income and fertilizer use. To test these predictions, we compared plant species composition and richness in residential lawns in seven U.S. metropolitan regions. We also compared species composition in lawns with understory vegetation in minimally-managed reference areas in each city. As expected, the composition of cultivated turfgrasses was more similar among lawns than among reference areas, but this pattern also held among spontaneous species. Plant species richness and diversity varied more among lawns than among reference areas, and more diverse lawns occurred in metropolitan areas with higher precipitation. Native forb diversity increased with precipitation and decreased with income, driving overall lawn diversity trends with these predictors as well. Our results showed that both management and regional climate shaped lawn species composition, but the overall homogeneity of species regardless of regional context strongly suggested that management was a more important driver.
Convergence of microclimate in residential landscapes across diverse cities in the United States
Hall, Sharon J.; Learned, Jennifer; Ruddell, Benjamin L.; Larson, K. L.; Cavender-Bares, Jeannine; Bettez, Neil; Groffman, Peter M.; Grove, J. Morgan; Heffernan, James B.; Hobbie, Sarah E.; Morse, Jennifer L.; Neill, Christopher; Nelson, Kristen C.; O'Neil-Dunne, Jarlath P.M.; Ogden, Laura A.; Pataki, Diane E.; Pearse, William D.; Polsky, Colin; Chowdhury, Rinku Roy; Steele, Meredith K.; Trammell, Tara L. E. (2016-01)
The urban heat island (UHI) is a well-documented pattern of warming in cities relative to rural areas. Most UHI research utilizes remote sensing methods at large scales, or climate sensors in single cities surrounded by standardized land cover. Relatively few studies have explored continental-scale climatic patterns within common urban microenvironments such as residential landscapes that may affect human comfort. We tested the urban homogenization hypothesis which states that structure and function in cities exhibit ecological "sameness" across diverse regions relative to the native ecosystems they replaced. We deployed portable micrometeorological sensors to compare air temperature and humidity in residential yards and native landscapes across six U.S. cities that span a range of climates (Phoenix, AZ; Los Angeles, CA; Minneapolis-St. Paul, MN; Boston, MA; Baltimore, MD; and Miami, FL). Microclimate in residential ecosystems was more similar among cities than among native ecosystems, particularly during the calm morning hours. Maximum regional actual evapotranspiration (AET) was related to the morning residential microclimate effect. Residential yards in cities with maximum AET < 50-65 cm/year (Phoenix and Los Angeles) were generally cooler and more humid than nearby native shrublands during summer mornings, while yards in cities above this threshold were generally warmer (Baltimore and Miami) and drier (Miami) than native forests. On average, temperature and absolute humidity were similar to 6 % less variable among residential ecosystems than among native ecosystems from diverse regions. These data suggest that common residential land cover and structural characteristics lead to microclimatic convergence across diverse regions at the continental scale.
Creating Native Plant Educational Materials through Virginia Cooperative Extension Publications
Seekford, Sierra A.; Fox, Laurie J.; Niemiera, Alexander X.; Steele, Meredith K. (Virginia Tech, 2023-12-12)
Virginia Cooperative Extension (VCE) has been a reputable source of research-based information for over 100 years. This information is provided through various forms such as field days, demonstrations, volunteer services and written materials in the form of publications. Peer reviewed publications are scholarly works and undergo reviews from experts in the field. Currently there are no VCE publications about native plants and their benefits. Materials from other organizations and such as the Virginia Department of Environmental Quality’s Plant Virginia Natives Campaign regional guides, Department of Conservation and Recreation brochures and the Digital Atlas of Virginia Flora online database have been used in VCE programming efforts. Plant Virginia Natives has been a leader in the movement to raise awareness, demand for native plants throughout the state, and has developed guides for ten regions across Virginia. By increasing the awareness of native plants, pollinators, and wildlife, local ecosystems will benefit greatly. Incorporating native plants into landscapes is especially critical because a review of 16 studies shows that the global population of insects has decreased by 45% in 40 years (Dirzo et al., 2014). Native plants provide essential support for insects. One of the barriers identified to planting more native plants is the lack of knowledge or confidence in people’s knowledge of the subject (Plant RVA Natives Steering Team, 2021). To address the lack of resources from VCE and the need for supplemental education materials, I have developed a three-part publication series on native plants. This series will promote native plants in the landscape by helping homeowners understand what native plants are, their benefits, how to use them in the landscape and how to maintain them for long term sustainability and resilience of landscapes.
Drivers of plant species richness and phylogenetic composition in urban yards at the continental scale
Cubino, Josep Padullés; Cavender-Bares, Jeannine; Hobbie, Sarah E.; Pataki, Diane E.; Avolio, Meghan L.; Darling, Lindsay E.; Larson, Kelli L.; Hall, Sharon J.; Groffman, Peter M.; Trammell, Tara L. E.; Steele, Meredith K.; Grove, J. Morgan; Neill, Christopher (2018-11-23)
Context As urban areas increase in extent globally, domestic yards play an increasingly important role as potential contributors to ecosystem services and well-being. These benefits largely depend on the plant species richness and composition of yards. Objectives We aim to determine the factors that drive plant species richness and phylogenetic composition of cultivated and spontaneous flora in urban yards at the continental scale, and how these potential drivers interact. Methods We analyzed plant species richness and phylogenetic composition of cultivated and spontaneous flora of 117 private yards from six major metropolitan areas in the US. Yard plant species richness and phylogenetic composition were expressed as a function of biophysical and socioeconomic variables and yard characteristics using linear mixed-effects models and spatially explicit structural equation modeling. Results Extreme temperatures largely determined yard species richness and phylogenetic composition at the continental scale. Precipitation positively predicted spontaneous richness but negatively predicted cultivated richness. Only the phylogenetic composition of the spontaneous flora was associated with precipitation. The effect of lower temperatures and precipitation on all yard diversity parameters was partly mediated by yard area. Among various socioeconomic variables, only education level showed a significant effect on cultivated phylogenetic composition. Conclusions Our results support the hypothesis that irrigation compensates for precipitation in driving cultivated yard plant diversity at the continental scale. Socioeconomic variables among middle and upper class families have no apparent influence on yard diversity. These findings inform the adaptation of US urban vegetation in cities in the face of global change.
Ecological homogenization of soil properties in the American residential macrosystem
Ryan, Christopher D.; Groffman, Peter M.; Grove, J. Morgan; Hall, Sharon J.; Heffernan, James B.; Hobbie, Sarah E.; Locke, Dexter H.; Morse, Jennifer L.; Neill, Christopher; Nelson, Kristen C.; O'Neil-Dunne, Jarlath; Chowdhury, Rinku Roy; Steele, Meredith K.; Trammell, Tara L. E. (Wiley, 2022-09)
The conversion of native ecosystems to residential ecosystems dominated by lawns has been a prevailing land-use change in the United States over the past 70 years. Similar development patterns and management of residential ecosystems cause many characteristics of residential ecosystems to be more similar to each other across broad continental gradients than that of former native ecosystems. For instance, similar lawn management by irrigation and fertilizer applications has the potential to influence soil carbon (C) and nitrogen (N) pools and processes. We evaluated the mean and variability of total soil C and N stocks, potential net N mineralization and nitrification, soil nitrite (NO2-)/nitrate (NO3-) and ammonium (NH4+) pools, microbial biomass C and N content, microbial respiration, bulk density, soil pH, and moisture content in residential lawns and native ecosystems in six metropolitan areas across a broad climatic gradient in the United States: Baltimore, MD (BAL); Boston, MA (BOS); Los Angeles, CA (LAX); Miami, FL (MIA); Minneapolis-St. Paul, MN (MSP); and Phoenix, AZ (PHX). We observed evidence of higher N cycling in lawn soils, including significant increases in soil NO2-/NO3-, microbial N pools, and potential net nitrification, and significant decreases in NH4+ pools. Self-reported yard fertilizer application in the previous year was linked with increased NO2-/ NO3- content and decreases in total soil N and C content. Self-reported irrigation in the previous year was associated with decreases in potential net mineralization and potential net nitrification and with increases in bulk density and pH. Residential topsoil had higher total soil C than native topsoil, and microbial biomass C was markedly higher in residential topsoil in the two driest cities (LAX and PHX). Coefficients of variation for most biogeochemical metrics were higher in native soils than in residential soils across all cities, suggesting that residential development homogenizes soil properties and processes at the continental scale.
Ecosystem services in managing residential landscapes: priorities, value dimensions, and cross-regional patterns
Larson, K. L.; Nelson, Kristen C.; Samples, S. R.; Hall, Sharon J.; Bettez, Neil; Cavender-Bares, Jeannine; Groffman, Peter M.; Grove, J. Morgan; Heffernan, James B.; Hobbie, Sarah E.; Learned, Jennifer; Morse, Jennifer L.; Neill, Christopher; Ogden, Laura A.; O'Neil-Dunne, Jarlath P.M.; Pataki, Diane E.; Polsky, Colin; Chowdhury, Rinku Roy; Steele, Meredith K.; Trammell, Tara L. E. (2016-03)
Although ecosystem services have been intensively examined in certain domains (e.g., forests and wetlands), little research has assessed ecosystem services for the most dominant landscape type in urban ecosystems-namely, residential yards. In this paper, we report findings of a cross-site survey of homeowners in six U.S. cities to 1) examine how residents subjectively value various ecosystem services, 2) explore distinctive dimensions of those values, and 3) test the urban homogenization hypothesis. This hypothesis posits that urbanization leads to similarities in the social-ecological dynamics across cities in diverse biomes. By extension, the thesis suggests that residents' ecosystem service priorities for residential landscapes will be similar regardless of whether residents live in the humid East or the arid West, or the warm South or the cold North. Results underscored that cultural services were of utmost importance, particularly anthropocentric values including aesthetics, low-maintenance, and personal enjoyment. Using factor analyses, distinctive dimensions of residents' values were found to partially align with the Millennium Ecosystem Assessment's categories (provisioning, regulating, supporting, and cultural). Finally, residents' ecosystem service priorities exhibited significant homogenization across regions. In particular, the traditional lawn aesthetic (neat, green, weed-free yards) was similarly important across residents of diverse U.S. cities. Only a few exceptions were found across different environmental and social contexts; for example, cooling effects were more important in the warm South, where residents also valued aesthetics more than those in the North, where low-maintenance yards were a greater priority.
Effects of Freshwater Salinization and Associated Base Cations on Bacterial Ecology and Water Quality
DeVilbiss, Stephen Edward (Virginia Tech, 2021-01-05)
Anthropogenic freshwater salinization, which is caused by numerous human activities including agriculture, urbanization, and deicing, impacts an estimated 37% of the contiguous drainage area in the United States. High salt concentrations in brackish and marine environments (~1,500 – 60,000 µS cm-1) influence aquatic bacteria. Less is known about the effects of freshwater salt concentrations (≤ 1,500 µS cm-1) on bacterial ecology, despite the pervasiveness of freshwater salinization. Bacteria perform many fundamental ecosystem processes (e.g. biogeochemical cycling) and serve as indicators of human health risk from exposure to waterborne pathogens. Thus, to understand how salt pollution affects freshwater ecosystems, there is a critical need to understand how freshwater salinization is impacting bacterial ecology. Using a series of controlled mesocosm experiments, my objectives were to determine how (1) survival of fecal indicator bacteria (FIB), (2) the diversity of native freshwater bacterial communities, and (3) bacterial respiration and nutrient uptake rates responded across a freshwater salinity gradient of different salt profiles. Survival rates (t90) of Escherichia coli, the EPA recommended freshwater FIB, increased by over 200% as salinity increased from 30 to 1,500 µS cm-1. Survival rates were also significantly higher in water with elevated Mg2+ relative to other base cations, suggesting that different salt sources and ion profiles can have varied effects in FIB survival. Thus, freshwater salinization could cause accumulating concentrations of FIB even without increased loading, increasing the risk of bacterial impairment. Diversity of native bacterial communities also varied across a freshwater salinity gradient, with a general increase in species richness as salinity reached 1,500 µS cm-1. Community variability (β-diversity) was greatest at intermediate salinities of 125 – 350 µS cm-1 and decreased towards the upper and lower extremes (30 and 1,500 µS cm-1, respectively). These diversity patterns suggest that osmotic stress is an environmental filter, but filtering strength is lowest at intermediate salinities causing a change from more deterministic to more stochastic assembly mechanisms. Different salt types also produced distinct bacterial community structures. Lastly, bacterial respiration doubled as salinity increased to 350 – 800 µS cm-1, revealing a subsidy-stress response of bacterial respiration across a freshwater salinity gradient. Corresponding changes in nitrogen and phosphorus uptake increased N:P ratios in ambient water, especially in mesocosms with elevated Ca2+, which could affect nutrient limitation in salinized streams enriched with Ca2+. Bacterial community structure based on Bray-Curtis dissimilarity was not correlated to pairwise changes in respiration rates but was linked to net nitrogen and phosphorus uptake after five days. Collectively, these results establish that freshwater salinization alters bacterial ecology at the individual population, whole community, and ecosystem process scales. Further, different salt types (e.g., CaCl2, MgCl2, NaCl, KCl, sea salt) had varying effects on bacteria at all levels and should be considered when predicting the effects of salinization on freshwater ecosystems. Developing more nuanced salt management plans that consider not only amount, but different types, of salts in freshwaters could help improve our ability to predict human health risk from waterborne pathogens and mitigate/ reduce salinity-induced impacts to freshwater ecosystem processes and services.
Future Global Soil Respiration Rates Will Swell Despite Regional Decreases in Temperature Sensitivity Caused by Rising Temperature
Jian, Jinshi; Steele, Meredith K.; Day, Susan D.; Thomas, R. Quinn (American Geophysical Union, 2018)
Between 1960 and 2014, the global soil respiration (RSG) flux increased at a rate of 0.05 Pg C year⁻¹; however, future increase is uncertain due to variations in projected temperature and regional heterogeneity. Regional differences in the sensitivity of soil respiration (RS) to temperature may alter the overall increase in rates of RS because the RS rates of some regions may decelerate while others continue to rise. Using monthly global RS data, we modeled the relationship between RS and temperature for the globe and eight climate regions and estimated RSG between 1961 and 2100 using historical (1961–2014) and future (2015–2100) temperature data [Representative Concentration Pathways (RCP2.6 and RCP8.5)]. Importantly, our approach allowed for estimation of regional sensitivity, where respiration rates may peak or decline as temperature rises. Estimated historical RSG increase (0.05 Pg C year⁻¹) was similar to the RSG increase of previous estimates. However, under the RCP8.5 scenario, which estimates approximately 3 °C of warming globally, the forecasted acceleration of RSG increased to an average of 0.12 Pg C year⁻¹. Under RCP8.5, the temperature sensitivity of RS declined in the arid, winter-dry temperate, and tropic. These regional declines were offset by increased RS sensitivity and fluxes from the boreal and polar regions. In contrast, under RCP2.6 RSG decelerated slightly from current rates. If rising greenhouse gas emission remains unmitigated, future increases in RSG will be much faster than current and historical rates, thereby possibly enhancing future losses of soil carbon and contributing to positive feedback loops of climate change.
Global soil respiration: interaction with macroscale environmental variables and response to climate change
Jian, Jinshi (Virginia Tech, 2018-02-05)
The response of global soil respiration (Rs) to climate change determines how long the land can continue acting as a carbon sink in the future. This dissertation research identifies how temporal and spatial variation in environmental factors affects global scale Rs modeling and predictions of future Rs under global warming. Chapter 1 describes the recommend time range for measuring Rs across differing climates, biomes, and seasons and found that the best time for measuring the daily mean Rs is 10:00 am in almost all climates and biomes. Chapter 2 describes commonly used surrogates in Rs modeling and shows that air temperature and soil temperature are highly correlated and that they explain similar amounts of Rs variation; however, average monthly precipitation between 1961 and 2014, rather than monthly precipitation for a specific year, is a better predictor in global Rs modeling. Chapter 3 quantifies the uncertainty generated by four different assumptions of global Rs models. Results demonstrate that the time-scale of the data, among other sources, creates a substantial difference in global estimates, where the estimate of global annual Rs based on monthly Rs data (70.85 to 80.99 Pg C yr-1) is substantially lower than the current benchmark for land models (98 Pg C yr-1). Chapter 4 simulates future global Rs rates based on two temperature scenarios and demonstrates that temperature sensitivity of Rs will decline in warm climates where the level of global warming will reach 3°C by 2100 relative to current air temperature; however, these regional decelerations will be offset by large Rs accelerations in the boreal and polar regions. Chapter 5 compares CO2 fluxes from turfgrass and wooded areas of five parks in Blacksburg, VA and tests the ability of the Denitrification-Decomposition model to estimate soil temperature, moisture and CO2 flux across the seasons. Cumulatively, this work provides new insights into the current and future spatial and temporal heterogeneity of Rs and its relationship with environmental factors, as well as key insights in upscaling methodology that will help to constrain global Rs estimates and predict how global Rs will respond to global warming in the future.
Homogenization of plant diversity, composition, and structure in North American urban yards
Pearse, William D.; Cavender-Bares, Jeannine; Hobbie, Sarah E.; Avolio, Meghan L.; Bettez, Neil; Chowdhury, Rinku Roy; Darling, Lindsay E.; Groffman, Peter M.; Grove, J. Morgan; Hall, Sharon J.; Heffernan, James B.; Learned, Jennifer; Neill, Christopher; Nelson, Kristen C.; Pataki, Diane E.; Ruddell, Benjamin L.; Steele, Meredith K.; Trammell, Tara L. E. (Ecological Society of America, 2018-02)
Urban ecosystems are widely hypothesized to be more ecologically homogeneous than natural ecosystems. We argue that urban plant communities assemble from a complex mix of horticultural and regional species pools, and evaluate the homogenization hypothesis by comparing cultivated and spontaneously occurring urban vegetation to natural area vegetation across seven major U.S. cities. There was limited support for homogenization of urban diversity, as the cultivated and spontaneous yard flora had greater numbers of species than natural areas, and cultivated phylogenetic diversity was also greater. However, urban yards showed evidence of homogenization of composition and structure. Yards were compositionally more similar across regions than were natural areas, and tree density was less variable in yards than in comparable natural areas. This homogenization of biodiversity likely reflects similar horticultural source pools, homeowner preferences, and management practices across U.S. cities.
Leveraging the NEON Airborne Observation Platform for socio-environmental systems research
Ordway, Elsa M.; Elmore, Andrew J.; Kolstoe, Sonja; Quinn, John E.; Swanwick, Rachel; Cattau, Megan; Taillie, Dylan; Guinn, Steven M.; Chadwick, K. Dana; Atkins, Jeff W.; Blake, Rachael E.; Chapman, Melissa; Cobourn, Kelly M.; Goulden, Tristan; Helmus, Matthew R.; Hondula, Kelly; Hritz, Carrie; Jensen, Jennifer; Julian, Jason P.; Kuwayama, Yusuke; Lulla, Vijay; O'Leary, Donal; Nelson, Donald R.; Ocon, Jonathan P.; Pau, Stephanie; Ponce-Campos, Guillermo E.; Portillo-Quintero, Carlos; Pricope, Narcisa G.; Rivero, Rosanna G.; Schneider, Laura; Steele, Meredith K.; Tulbure, Mirela G.; Williamson, Matthew A.; Wilson, Cyril (2021-06)
During the 21st century, human-environment interactions will increasingly expose both systems to risks, but also yield opportunities for improvement as we gain insight into these complex, coupled systems. Human-environment interactions operate over multiple spatial and temporal scales, requiring large data volumes of multi-resolution information for analysis. Climate change, land-use change, urbanization, and wildfires, for example, can affect regions differently depending on ecological and socioeconomic structures. The relative scarcity of data on both humans and natural systems at the relevant extent can be prohibitive when pursuing inquiries into these complex relationships. We explore the value of multitemporal, high-density, and high-resolution LiDAR, imaging spectroscopy, and digital camera data from the National Ecological Observatory Network's Airborne Observation Platform (NEON AOP) for Socio-Environmental Systems (SES) research. In addition to providing an overview of NEON AOP datasets and outlining specific applications for addressing SES questions, we highlight current challenges and provide recommendations for the SES research community to improve and expand its use of this platform for SES research. The coordinated, nationwide AOP remote sensing data, collected annually over the next 30 yr, offer exciting opportunities for cross-site analyses and comparison, upscaling metrics derived from LiDAR and hyperspectral datasets across larger spatial extents, and addressing questions across diverse scales. Integrating AOP data with other SES datasets will allow researchers to investigate complex systems and provide urgently needed policy recommendations for socio-environmental challenges. We urge the SES research community to further explore questions and theories in social and economic disciplines that might leverage NEON AOP data.
Locational and temporal patterns in microorganisms potentially affecting water quality in the Dan River system
Cappellin, Catherine Brooks (Virginia Tech, 2019-09-06)
River ecosystems across the US and globally face numerous stressors that impact both ecological function and water quality. In 2015-16, municipalities along the Dan River in southern Virginia experienced repeated taste and odor (TandO) issues in their drinking water that originated from the river source water. Given that the source of TandO issues during these events were unknown, this research aimed to identify patterns in the distributions of river microorganisms that could help identify potential biological causes. Monthly water, sediment, and periphyton samples were collected for a full year from the Smith and Dan Rivers to quantify actinomycete, fungi, and chlorophyll a concentrations, which have historically been linked to TandO problems, and to characterize changes in microbial community structure. Although no significant TandO event occurred during the study period, the work produced unique and valuable data that describe patterns of microbial populations and communities in a river ecosystem. Results from the study show the abundances of actinomycetes, fungi, and chlorophyll a expressing seasonal and regional variation by habitat. From a broader ecological perspective, microbial communities sampled from water, sediment, and periphyton were each unique from each other regardless of river reach and season sampled. Overall, this research adds to our understanding of river ecology by detailing the microbial abundance and diversity in three river habitats, including periphyton, that can be used to predict sources of river TandO in future events, and offers new questions regarding how microbial diversity changes over space and time.
Managing Landscapes to Meet Emerging Global Challenges
Badgley, Brian D.; Daniels, W. Lee; Day, Susan D.; Eick, Matthew J.; Ervin, Erik H.; Steele, Meredith K.; Stewart, Ryan D.; Strahm, Brian D.; Xia, Kang; Zipper, Carl E. (Virginia Tech, 2017-05-15)
Our vision is to create a program dedicated to accelerating innovation that improves the quality, efficiency, and resilience of human dominated landscapes, including our cities, farms, and industrial lands. Humans dramatically alter and manipulate the global landscape for food and fiber production, mineral extraction, urban development, waste disposal and many other purposes. Impacts to essential ecosystem functions and values range from local (e.g. mining and land development) to global (e.g. carbon emissions) with a clear need for development of appropriate management systems for their mitigation. By using a systems approach that interfaces environmental scientists and ecologists with relevant disciplines, this proposed signature area within Global Systems Science (GSS) will build upon existing group strengths in soil remediation, water quality, hydrology, urban soils, land reclamation, agroecosystem management, forest ecology, wetland restoration, soil-waste management and integrated modeling across multiple spatial and temporal scales to develop a more holistic approach to landscape management. We will also...
Moving Virginia Dairy Farms Toward Phosphorus Balance
Pearce, Austin Willis (Virginia Tech, 2020-08-24)
Sustainability for Virginia dairy farms requires balancing phosphorus (P) imports and exports at the farm-gate level. Balancing P helps prevent further accumulation of P in farm soils through routine applications of manure, which over time contributes to surface water quality issues. The objectives of this research centered on guiding dairy farms in Virginia toward lower, more sustainable P balance, and without adversely impacting profitability. First, the state of P balance had to be determined for a sample of dairy farms, including risk factors for excessively high P balance. Second, a repeated assessment of P balance on those dairy farms sought to determine any key factors of change in P balance between years. Lastly, a small Virginia dairy farm was used as a case farm to evaluate whether or not it could reduce its P balance while maintaining or improving farm profitability. An initial assessment of 58 dairy farms in Virginia showed that 75% of farms could operate with a P balance less than 18.7 kg ha-1. The two risk factors that led to excessively high P surpluses were the use of poultry litter and excessive P imported with purchased feed. The repeated assessment included 30 of the 58 original dairy farms. Increases of 1.0 kg P ha-1 of total P imports and exports were respectively correlated to a mean P balance increase of 0.76 kg ha-1 and a mean P balance decrease of 0.43 kg ha-1, suggesting that changes in P imports affect changes in P balance more than changes in P exports. Reduced poultry litter use was highly correlated to reduced P balance, and increasing cow manure exports also reduced P balance for the farms with the opportunity. As a significant portion of the farms assessed were small (less than 200 milking cows), a case farm of 105 cows on 100 acres was used to explore how farm profitability could be affected as P balance was reduced through additional acres, increased crop production, and with a grazing-based farming strategy. Results from partial budget analysis showed that after expanding the land base from 100 to 150 acres for crop production, the change in potential net return ranged from $-0.90 to $1.26/cwt of milk, with accompanying changes in P balance ranging from -9.0 to -14.7 lbs/ac. The analysis also showed that changes in potential net returns after converting to a grazing-based system ranged from $-2.14 to $1.39/cwt, with greater change in P balance ranging from -9.7 to -17.8 lbs/ac. The most profitable strategy, generally, for this farm seemed to be expanding the land base and growing a cash crop. Phosphorus balance on Virginia dairy farms can be reduced, potentially without negative impacts on farm net return, though challenges remain for farms with limited land or areas with high density of animal agriculture.
Quantifying the Effects of Watershed Size and Land Development on Stream Nutrients
Ogunmayowa, Oluwatosin Thompson (Virginia Tech, 2020-05-14)
Excessive nutrient loading from watersheds causes nutrient enrichment and water quality issues in very small streams to large rivers. Nutrient enrichment is exacerbated by urbanization and agricultural land use; however, the magnitude of the problem differs by regional landscape and environmental characteristics. Currently, we do not understand how regional variables moderate these relationships. Thus, the overall objective of this thesis was to investigate how regional landscape and environmental variables moderate developed land cover–stream nutrient relationships across the United States. The first study examined how climate and land use influences the scaling of phosphorus, total nitrogen, ammonia and nitrate loads for very large regions (Mid-Atlantic, Upper Mississippi, Ohio and Missouri) of the U.S. Results show the scaling relationships of nutrient loads with watershed size depends on the nutrient species and differed by region; the magnitude of the relationships was greater in wetter climates and developed watersheds. The second study determined 1) whether the relationships between urban and agricultural land cover intensity and concentrations of phosphorus, total nitrogen, ammonia and nitrate across the U.S., differed by ecoregion, and 2) whether regional landscape and environmental factors explained those differences. The relationships were found to differ by ecoregion and the differences were moderated by regional agriculture, topography and climate where stream nutrients increased more rapidly with anthropogenic land use in regions with high agricultural land use, wetter climates and flatter topography. The study findings will enable water quality managers create region-specific water management strategies for streams impacted by excessive nutrient loads.
Sediment chemistry of urban stormwater ponds and controls on denitrification
Blaszczak, Joanna R.; Steele, Meredith K.; Badgley, Brian D.; Heffernan, James B.; Hobbie, Sarah E.; Morse, Jennifer L.; Rivers, Erin N.; Hall, Sharon J.; Neill, Christopher; Pataki, Diane E.; Groffman, Peter M.; Bernhardt, Emily S. (Ecological Society of America, 2018-06)
Stormwater ponds and retention basins are ubiquitous features throughout urban landscapes. These ponds are potentially important control points for nitrogen (N) removal from surface water bodies via denitrification. However, there are possible trade-offs to this water quality benefit if high N and contaminant concentrations in stormwater pond sediments decrease the complete reduction of nitrous oxide (N2O), a potent greenhouse gas, to dinitrogen (N-2) during denitrification. This may occur through decreasing the abundance or efficiency of denitrifiers capable of producing the N2O reductase enzyme. We predicted that ponds draining increasingly urbanized landscapes would have higher N and metal concentrations in their sediments, and thereby greater N2O yields. We measured potential denitrification rates, N2O reductase (nosZ) gene frequencies, as well as sediment and pore water chemistry in 64 ponds distributed across eight U.S. cities. We found almost no correlation between the proportion of urban land cover surrounding ponds and the nutrient and contaminant concentrations in the stormwater pond sediments within or across all cities. Regression analysis revealed that the proportion of potential N-2 and N2O production that could be explained was under different environmental controls. Our survey raises many new questions about why N fluxes and transformations vary so widely both within and across urban environments, but also allays the concern that elevated metal concentrations in urban stormwater ponds will increase N2O emissions. Urban stormwater ponds are unlikely to be a problematic source of N2O to the atmosphere, no matter their denitrification potential.
Urban soil carbon and nitrogen converge at a continental scale
Trammell, Tara L. E.; Pataki, Diane E.; Pouyat, Richard, V; Groffman, Peter M.; Rosier, Carl; Bettez, Neil; Cavender-Bares, Jeannine; Grove, J. Morgan; Hall, Sharon J.; Heffernan, James B.; Hobbie, Sarah E.; Morse, Jennifer L.; Neill, Christopher; Steele, Meredith K. (2020-05)
In urban areas, anthropogenic drivers of ecosystem structure and function are thought to predominate over larger-scale biophysical drivers. Residential yards are influenced by individual homeowner preferences and actions, and these factors are hypothesized to converge yard structure across broad scales. We examined soil total C and total delta C-13, organic C and organic delta C-13, total N, and delta N-15 in residential yards and corresponding reference ecosystems in six cities across the United States that span major climates and ecological biomes (Baltimore, Maryland; Boston, Massachusetts; Los Angeles, California; Miami, Florida; Minneapolis-St. Paul, Minnesota; and Phoenix, Arizona). Across the cities, we found soil C and N concentrations and soil delta N-15 were less variable in residential yards compared to reference sites supporting the hypothesis that soil C, N, and delta N-15 converge across these cities. Increases in organic soil C, soil N, and soil delta N-15 across urban, suburban, and rural residential yards in several cities supported the hypothesis that soils responded similarly to altered resource inputs across cities, contributing to convergence of soil C and N in yards compared to natural systems. Soil C and N dynamics in residential yards showed evidence of increasing C and N inputs to urban soils or dampened decomposition rates over time that are influenced by climate and/or housing age across the cities. In the warmest cities (Los Angeles, Miami, Phoenix), greater organic soil C and higher soil delta C-13 in yards compared to reference sites reflected the greater proportion of C-4 plants in these yards. In the two warm arid cities (Los Angeles, Phoenix), total soil delta C-13 increased and organic soil delta C-13 decreased with increasing home age indicating greater inorganic C in the yards around newer homes. In general, soil organic C and delta C-13, soil N, and soil delta N-15 increased with increasing home age suggesting increased soil C and N cycling rates and associated C-12 and N-14 losses over time control yard soil C and N dynamics. This study provides evidence that conversion of native reference ecosystems to residential areas results in convergence of soil C and N at a continental scale. The mechanisms underlying these effects are complex and vary spatially and temporally.
Virginia Tech GIS & Remote Sensing 2014 Research Symposium - Converging Surface Water Distributions in US Cities and Agriculture Dr. Meredith Steele, Assistant Professor, Crop & Soil Environmental Sciences
Steele, Meredith K. (2014-05-13)
Converging Surface Water Distributions in US Cities and Agriculture Dr. Meredith Steele, Assistant Professor, Crop & Soil Environmental Sciences The annual 2014 Virginia Tech GIS and Remote Sensing Research Symposium provides a venue to share information about recent advances in geographic information systems and remote sensing applications and research. The Symposium focuses on interaction among participants and the sharing of data, applications, and techniques. It includes both presentation and poster sessions as well as a keynote speaker.
Water Fluxes in Soil-Pavement Systems: Integrating Trees, Soils and Infrastructure
de la Mota Daniel, Francisco Javier (Virginia Tech, 2019-01-31)
In urban areas, trees are often planted in bare soil sidewalk openings (tree pits) which recently are being covered with permeable pavements. Pavements are known to alter soil moisture and temperature, and may have implications for tree growth, root development and depth, drought resilience, and sidewalk lifting. Furthermore, tree pits are often the only unsealed soil surface and are important for water exchange between soil and atmosphere. Therefore, covering tree pits with pavement, even permeable, may have implications for the urban water balance and stormwater management. A better understanding of permeable pavement on tree pavement soil system functioning can inform improved tree pit and street design for greater sustainability of urban environments. We conducted experiments at two sites in Virginia, USA (Mountains and Coastal Plain) with different climate and soil. At each location, we constructed 24 tree pits in a completely randomized experiment with two factors: paved with resin-bound porous-permeable pavement versus unpaved, and planted with Platanus x acerifolia 'Bloodgood' versus unplanted (n = 6). We measured tree stem diameter, root growth and depth, and soil water content and temperature over two growing seasons. We also monitored tree sap flow one week in June 2017 at the Mountains. In addition, we calibrated and validated a soil water flow model, HYDRUS-1D, to predict soil water distribution for different rooting depths, soil textures and pavement thicknesses. Trees in paved tree pits grew larger, with stem diameters 29% (Mountains) and 51% (Coastal Plain) greater. Roots developed faster under pavement, possibly due to the increased soil water content and the extended root growing season (14 more days). Tree transpiration was 33% of unpaved and planted pit water outputs, while it was 64% for paved and planted pits. In June 2016, planted pits had decreased root-zone water storage, while unplanted pits showed increased storage. A water balance of the entire experimental site showed overall decreased soil water storage due to tree water extraction becoming the dominant factor. HYDRUS-1D provided overall best results for model validation at 10 cm depth from soil surface (NSE = 0.447 for planted and paved tree pits), compared to 30- and 60 cm depths. HYDRUS-1D simulations with greater pavement thickness resulted in changes in predicted soil water content at the Coastal Plain, with higher values at 10- and 30-cm depths, but lower values at 60-cm depth. At the Mountains, virtually no difference was observed, possibly due to different soil texture (sandy vs clayey). Tree pits with permeable pavement accelerated tree establishment, but promoted shallower roots, possibly increasing root-pavement conflicts and tree drought susceptibility. Paved tree pits resulted in larger trees, increasing tree transpiration, but reduced soil evaporation compared to unpaved pits. Larger bare soil pits surrounded by permeable pavement might yield the best results to improve urban stormwater retention. Also, HYDRUS 1D was successful at simulating soil water content at 10-cm depth and may be valuable to inform streetscape design and planning.

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