About

The Sweetman lab is part of the Department of Ecosystem Science and Management at Penn State University. Research focuses on understanding the impacts of climate change, population growth, and land use change on freshwater lakes and wetlands. The lab employs multidisciplinary and collaborative approaches, including paleolimnology and large-scale surveys.

Research topics

• Ecology
• Geography
• Environmental science
• Biology
• Meteorology
• Atmospheric sciences
• Oceanography
• Chemistry
• Geology

Selected publications

• Assessing the off-target movement of tebufenozide in forested ecosystems: implications for vernal pond ecosystems

  Environmental Monitoring and Assessment · 2026-01-03

  articleOpen accessSenior author

  The widespread use of pesticides has significantly contributed to managing pest populations in both agricultural and forest ecosystems, yet concerns about their unintended impacts on non-target habitats continue to grow. Tebufenozide, a pesticide commonly used to control forest defoliator pests, including spongy moth (Lymantria dispar dispar), is known for its selective action on Lepidopteran larvae. Despite its targeted mode of action, the potential transport and fate of tebufenozide into sensitive forested aquatic habitats, such as vernal ponds, is not well understood. This study examines the spatial distribution of tebufenozide in 41 vernal ponds located within three state forests in central Pennsylvania (Bald Eagle, Rothrock, and Tuscarora) by analyzing sediment and water samples collected within and outside designated spray blocks. Tebufenozide was detected in 39 water samples and 40 sediment samples, including 27 unsprayed water and sediment samples, indicating possible pesticide drift or runoff into non-target areas. We used a Mann-Whitney U test to reveal significantly higher concentrations of tebufenozide in ponds within spray blocks for both sediment (W = 241.5, p = 0.0161) and water (W = 316.5, p = 2.769e-06). Tebufenozide concentrations were higher in ponds closer to spray zones, suggesting proximity influences pesticide levels, though no clear directional dispersal patterns emerged. These findings underscore the vulnerability of vernal ponds, essential breeding habitats for amphibians and other organisms, to pesticide contamination. Enhanced management strategies, such as wider buffer zones and alternative pest control measures, may be necessary to safeguard these critical ecosystems.

  PublisherOA PDFDOI

• Stability of macroinvertebrate communities in vernal ponds following natural drying and refilling events

  Research Square · 2025-07-01

  preprintOpen accessSenior author
  PublisherOA PDFDOI

• Stability of macroinvertebrate communities in vernal ponds following natural drying and refilling events

  Wetlands Ecology and Management · 2025-09-20

  articleOpen accessSenior author

  Abstract Vernal ponds are vital components of forest ecosystems in the eastern United States, providing biodiversity support, water filtration, and flood regulation. Climate change may exacerbate hydrological fluctuations, altering the communities these seasonal wetlands support. This study examines the effects of drying disturbances on macroinvertebrate communities in vernal ponds, focusing on comparing biodiversity metrics before and after hydrological drawdown. We conducted weekly monitoring of pond inundation and macroinvertebrate sampling in five vernal ponds in Central Pennsylvania during 2023. We measured alpha diversity using species richness and Shannon diversity, and calculated temporal beta diversity with Jaccard’s dissimilarity index, examining turnover and nestedness. We found no significant changes in alpha diversity metrics between pre- and post-drying periods. However, we observed a trend toward greater species loss (77% of dissimilarity) compared to gains (23%). Beta diversity patterns of turnover and nestedness were stable across temporal and spatial scales, suggesting that drying disturbances did not significantly affect community structure. These findings contrast with previous studies reporting significant shifts in community composition, potentially due to the adaptive strategies of macroinvertebrates. This research highlights the need for long-term studies to assess drying intensity and informs conservation strategies for vernal pond ecosystems in the context of climate change.

  PublisherDOI

• Sediment microbial communities in long‐term wetland restorations within the Prairie Pothole Region of the United States

  Restoration Ecology · 2025-12-22

  articleOpen accessSenior authorCorresponding

  Hydrologic wetland restoration in the Prairie Pothole Region is a common management practice to facilitate habitat and ecosystem recovery after degradation or drainage. Little is known about the recovery of sediment microbial communities relative to other organisms, such as vegetation, fish, and macroinvertebrates, even though they are critical for overall ecosystem health. We collected benthic sediments from natural and restored wetlands, where restorations had occurred 26–33 years prior, to analyze microbial communities. We used 16S rRNA gene sequencing to investigate differences in the structure and predicted function of prokaryotic microbial communities among natural and restored wetland groups. Water pH, conductivity, temperature, and major ions were also measured to investigate differences among wetland groups, as well as to evaluate their potential influences on microbial community composition. We found no significant differences in any microbial metric or water quality variable among wetland groups. There were also no significant influences from water variables on microbial community composition. Overall, our results suggest that 26 years allows ample time for microorganisms to recover and resemble natural wetland communities. These findings could indicate that subsequent ecosystem functions may also recover within this time frame.

  PublisherOA PDFDOI

• Reviews and syntheses: Variable inundation across Earth's terrestrial ecosystems

  Biogeosciences · 2025-02-24 · 7 citations

  articleOpen accessCorresponding

  Abstract. The structure, function, and dynamics of Earth's terrestrial ecosystems are profoundly influenced by how often (frequency) and how long (duration) they are inundated with water. A diverse array of natural and human-engineered systems experience temporally variable inundation whereby they fluctuate between inundated and non-inundated states. Variable inundation spans extreme events to predictable sub-daily cycles. Variably inundated ecosystems (VIEs) include hillslopes, non-perennial streams, wetlands, floodplains, temporary ponds, tidal systems, storm-impacted coastal zones, and human-engineered systems. VIEs are diverse in terms of inundation regimes, water chemistry and flow velocity, soil and sediment properties, vegetation, and many other properties. The spatial and temporal scales of variable inundation are vast, ranging from sub-meter to whole landscapes and from sub-hourly to multi-decadal. The broad range of system types and scales makes it challenging to predict the hydrology, biogeochemistry, ecology, and physical evolution of VIEs. Despite all experiencing the loss and gain of an overlying water column, VIEs are rarely considered together in conceptual, theoretical, modeling, or measurement frameworks and approaches. Studying VIEs together has the potential to generate mechanistic understanding that is transferable across a much broader range of environmental conditions, relative to knowledge generated by studying any one VIE type. We postulate that enhanced transferability will be important for predicting changes in VIE function in response to global change. Here we aim to catalyze cross-VIE science that studies drivers and impacts of variable inundation across Earth's VIEs. To this end, we complement expert mini-reviews of eight major VIE systems with overviews of VIE-relevant methods and challenges associated with scale. We conclude with perspectives on how cross-VIE science can derive transferable understanding via unifying conceptual models in which the impacts of variable inundation are studied across multi-dimensional environmental space.

  PublisherOA PDFDOI

• Assessing the off-target movement of tebufenozide in forested ecosystems: Implications for vernal pond ecosystems

  Research Square · 2025-08-29

  preprintOpen accessSenior author
  PublisherOA PDFDOI

• Monitoring Long-term Microplastics Contamination and Influential Factors in Freshwater Sediment Cores in Pennsylvania, USA

  Proceedings of the World Congress on Civil, Structural, and Environmental Engineering · 2024-04-01

  articleOpen access
  PublisherOA PDFDOI

• Reviews and Syntheses: Variable Inundation Across Earth’s Terrestrial Ecosystems

  2024-03-08 · 3 citations

  preprintOpen accessCorresponding

  Abstract. The structure, function, and dynamics of Earth’s terrestrial ecosystems are profoundly influenced by the frequency and duration that they are inundated with water. A diverse array of natural and human engineered systems experience temporally variable inundation whereby they fluctuate between inundated and non-inundated states. Variable inundation spans from extreme flooding and droughts to predictable sub-daily cycles. Variably inundated ecosystems (VIEs) include hillslopes, non-perennial streams, wetlands, floodplains, temporary ponds, tidal systems, storm-impacted coastal zones, and human engineered systems. VIEs are diverse in terms of inundation regimes, water chemistry and flow velocity, soil and sediment properties, vegetation, and many other properties. The spatial and temporal scales of variable inundation are vast, ranging from sub-meter to whole landscapes and from sub-hourly to multi-decadal. The broad range of system types and scales makes it challenging to predict the hydrology, biogeochemistry, ecology, and physical evolution of VIEs. Despite all experiencing the loss and gain of an overlying water column, VIEs are rarely considered together in conceptual, theoretical, modeling, or measurement frameworks/approaches. Studying VIEs together has the potential to generate mechanistic understanding that is transferable across a much broader range of environmental conditions, relative to knowledge generated by studying any one VIE type. We postulate that enhanced transferability will be important for predicting VIE function under future, potentially non-analog, environmental conditions. Here we aim to catalyze cross-VIE science that studies drivers and impacts of variable inundation across Earth’s VIEs. To this end, we complement expert mini-reviews of eight major VIE systems with overviews of VIE-relevant methods and challenges associated with scale. We conclude with perspectives on how cross-VIE science can derive transferable understanding via a ‘continuum approach’ in which the impacts of variable inundation are studied across multi-dimensional environmental space.

  PublisherDOI

• Common Use Herbicides Increase Wetland Greenhouse Gas Emissions

  SSRN Electronic Journal · 2024-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Common use herbicides increase wetland greenhouse gas emissions

  The Science of The Total Environment · 2024-05-01 · 9 citations

  articleOpen accessSenior author

  Wetlands play a disproportionate role in the global climate as major sources and sinks of greenhouse gases. Herbicides are the most heavily used agrochemicals and are frequently detected in aquatic ecosystems, with glyphosate and 2,4-Dichlorophenoxyacetic acid (2,4-D), representing the two most commonly used worldwide. In recent years, these herbicides are being used in mixtures to combat herbicide-tolerant noxious weeds. While it is well documented that herbicide use for agriculture is expected to increase, their indirect effects on wetland greenhouse gas dynamics are virtually unknown. To fill this knowledge gap, we conducted a factorial microcosm experiment using low, medium, and high concentrations of glyphosate or 2,4-D, individually and in combination to investigate their effects on wetland methane, carbon dioxide, and nitrous oxide fluxes. We predicted that mixed herbicide treatments would have a synergistic effect on greenhouse gases compared to individual herbicides. Our results showed that carbon dioxide flux rates and cumulative emissions significantly increased from both individual and mixed herbicide treatments, whereas methane and nitrous oxide dynamics were less affected. This study suggests that extensive use of glyphosate and 2,4-D may increase carbon dioxide emissions from wetlands, which could have implications for climate change.

  PublisherDOI

Frequent coauthors

• David Mushet

  19 shared

• Kyle I. McLean

  United States Geological Survey

  17 shared

• John P. Smol

  Queen's University

  15 shared

• Brent B. Wolfe

  Wilfrid Laurier University

  9 shared

• Roland I. Hall

  University of Waterloo

  9 shared

• Lauren A. MacDonald

  Pennsylvania State University

  8 shared

• Kui Hu

  Yunnan Normal University

  7 shared

• Anna M. DeSellas

  Queen's University

  6 shared

Labs

• Sweetman LabPI

Education

• Ph.D., Biology

  Queen's University

  2006

• MS, Oceanography

  University of Alaska Fairbanks

  2001

• BSc (honours), Biology

  University of Regina

  1996

Awards & honors

• NSF GRFP Fellowship
• Cassel Undergraduate Research Scholarship
• EPSCoR Research Seed Grant