2007 REU Student Project Abstracts
Jennifer Croskrey, Northwest Missouri State University
Mentor: Dr. Mary Anne Carroll, University of Michigan
“Investigation of Ozone Stomatal Flux in a Northern Mixed Hardwood Forest during the 1999 to 2004 Growing Seasons”
Hourly ozone stomatal fluxes (Fs_O3) were calculated for the University of Michigan’s Biological Station (UMBS) forest in northern Michigan from June 15 to September 15 for each year from 1999 to 2004 based on a set of equations derived from a resistance analog model. Measurements key to the calculations include latent and sensible heat flux, wind speed, ambient ozone (O3), and leaf air index. These measurements were taken primarily at the 46 m height of the UMBS Flux Tower on site with the exception of ambient O3, taken at 35 m on the PROPHET Tower. The calculated Fs_O3 were used to investigate the effect O3 exposure might have on Net Ecosystem CO2 Exchange (NEE). Analysis of NEE and Fs_O3 required consideration of several variables known to significantly affect NEE, including photosynthetic photon flux density (PPFD), vapor pressure deficit (VPD), soil moisture, and air temperature. Statistical analyses based on these variables consistently produced results indicating that a statistically significant positive relationship exists between NEE and Fs_O3. These results are unexpected as Fs_O3 is expected to be negatively correlated with NEE as a result of pant damage from O3 exposure, but may simply reflect the strong positive relationship known to exist between NEE and stomatal conductance.
Gino Davis, Howard University
Mentor: Dr. Pat Kociolek, California Academy of Sciences
“Effects of Stream Velocity on Diatom Community Structure”
Effects on diatom community structure under high and low current velocities over a period of ten days were observed. Artificial stream channels were supplied with water directly from the East Branch of the Maple River. One current velocity was adjusted be ambient to a point chosen in the East Branch of the Maple River at 15cm/s and a current velocity was adjusted to be 3.75cm/s (¼ of the ambient). Significant changes (p=0.027) were observed in the Shannon-Wiener diversity with respect to current velocity. No significant changes were observed in the Shannon Wiener diversity with respect to time. Significant changes (p=0.007) in the relative abundance of the genus Synedra were observed with respect to current velocity. Significant changes (p=.011) were observed with respect to time in the relative abundance of the genera Navicula and Cymbella (grouped together due to taxonomical limitations).
Sydney Glassman, University of Pennsylvania
Mentor: Dr. David Karowe, Western Michigan University
“Effect of environmental factors on prey-derived nitrogen in sundews (Drosera rotundifolia) in a northern Michigan bog”
In this study, δ15N values of insectivorous plants, their prey, and non-carnivorous reference plants were used to determine the relative contributions of nitrogen originating from prey and soil to the nutrition of Drosera rotundifolia plants in a northern Michigan bog. To determine which environmental factors that most strongly affect the relative contributions of plant- and insect-derived N within a single population of carnivorous plants, soil pH, temperature, dissolved inorganic nitrogen (as NH4+), and insect availability adjacent to 26 sundew plants were measured. Stable nitrogen isotope analysis was used to determine which variable was most strongly correlated with the proportion of prey-derived nitrogen across plants. This study provided a test of the hypothesis that carnivory evolved in acidic, low-nutrient habitats largely because low pH inhibits decomposition, thereby reducing the availability of plant-derived nitrogen and creating strong selection for modification of leaves into structures capable of capturing insect nitrogen. The population of Drosera rotundifolia was found to derive an average of 44% of its nitrogen from prey. However, the variation among individuals and thus the relative importance of carnivory varied across individuals by almost 4-fold. Neither pH nor temperature, nor insect availability as a whole were significantly correlated with the proportion of prey-derived nitrogen. The commonly held belief that pH slows decomposition which decreases ammonium availability did not appear be upheld in this bog. The major driver of the relative importance of carnivory in Mud Lake Bog may be the abundance of small, weak flying prey that are likely to be attracted to the red glistening leaves of sundews such as midges.
Stephanie Levy, University of Michigan
Mentor: Dr. Allison Snow, Ohio State University
“The invasiveness of the cattail hybrid Typha x glauca: a study of seedling growth rates”
Hybridization may play an important role in the formation of invasive species. Throughout North American wetlands the native cattail species Typha latifolia is hybridizing with the introduced species Typha angustifolia. It has been suggested that the hybrid cattail species Typha x glauca is experiencing hybrid vigor and is therefore more invasive than its parent taxa. The objective of this study was to examine whether Typha x glauca is in fact more invasive than its parent taxa by studying the growth patterns of Typha seedlings. The seedlings used in this experiment fit into five different species groups: T. angustifolia, T. latifolia, hybrids produced by pollinating T. angustifolia with T. latifolia, hybrids produced by pollinating T. latifolia with T. angustifolia, and backcrosses produced by pollinating T. x glauca with T. angustifolia. This study consisted of a factorial design experiment that manipulated the environmental conditions of soil moisture and soil nutrients. Data from a previous study examining variation in percent germination between T. latifolia, T. angustifolia and T. x glauca was analyzed. The data from the seedling experiment did not suggest that the F1 T. x glauca seedlings were experiencing hybrid vigor. Instead, the T. x glauca backcross seedlings were the most successful. Further research should be conducted examining the success of advanced hybrids.
Andrew Miller, Ursinas College
Mentor: Dr. Paul Webb, University of Michigan
“The Effects of Natural Turbulence on Diurnal Fish Community Assemblages, Distribution, and Habitat Selection”
The study of fish community assemblages and the myriad factors that determine their makeup, including wind-driven turbulence on lakes, is of great importance to fisheries resource management and policy. Studies done on coral reefs have concluded that morphology differences play important roles in the way fish react to turbulence. Translating this concept to a freshwater system, this study looked at turbulence on South Fishtail Bay, Douglas Lake, Michigan, and its effects on fish distributions and assemblages. Based on the morphological measure of body depth, it was hypothesized that deeper-bodied species, such as sunfish and perch, would show a greater aversion to turbulence than would shallow-bodies species, such as minnows. Data was limited and was sufficient only to corroborate the notion that yellow perch (Perca flavescens) and smallmouth bass (Micropterus dolomieui) do indeed seek refuge from turbulence in deeper waters, though results regarding the other species were inconclusive. A more thorough, all-encompassing method of data collection and analysis is a critical next step in assessing the relationship between turbulence and fish communities.
Tyra Pendergrass, Howard University
Mentors: Drs. Peter Curtis and Chris Gough, Ohio State University & Dr. Chris Vogel, University of Michigan
“The Effects of Tree Girdling on Soil and Bole Respiration in Big Tooth Aspen Trees (Populus grandidentata)”
Much attention has been given to the effects of anthropogenic activities on the global carbon cycle. Deforestation and the burning of fossil fuels has added vast amounts of carbon to the atmosphere, while at the same time reducing the number of carbon sinks that are available to sequester the carbon. The focus of this study was to determine the effects of a selected disturbance (tree girdling) on a forest’s ability to remain a carbon sink, or transform into a carbon source. A field experiment was conducted on the site of the University of Michigan Biological Station in Pellston, Michigan. Six plots containing Aspen trees were set-up in a block design. All of the trees in the experimental plots were girdled. The soil respiration and bole respiration rates were measured at designated time interval over a period of 26 days. A strong efflux decline trend was observed in the soil of plots where the trees were girdled. However, when a paired t-test was performed only one time interval provide a p value that was significant (p=0.014). Trees that were girdled in March-June of 2007 and July 2006 were included in the bole respiration data. It was found that in all but one of the trees, the area above the girdled area had the highest efflux value; followed by the area below the girdled area and finally the girdled area with the lowest efflux value. It was also found that the trees that were girdled prior to July 2007 had a substantially higher average efflux above the girdled area when compared to the trees that were girdled in July 2007 (9.86 μmol/m2/sec and 4.67 μmol/m2/sec, respectively).
Callie Plafkin, Swarthmore College
Mentor: Dr. Troy Keller, Columbus State University
“Water Velocity and Light Intensity Effects on Carbon Stable Isotope Ratios (d13C) of Cladophora glomerata”
Intraspecific variability in aquatic autotrophic carbon isotope ratios, d13C, contests the precision and accuracy of current methods of producer-consumer association with stable isotope analyses. In attempt to understand the influence of physical environmental factors on d13C signatures of aquatic producers, the effects of water velocity and irradiance on d13C were examined in Cladophora glomerata with a controlled flume experiment. A highly significant inverse relationship was observed between water velocity and C. glomerata d13C, likely due to velocity effects on boundary layer and carbon dioxide diffusion limitation. Light regime was not found be a significant independent affecter of d13C, but did exert an interactive effect with velocity, accentuating degree/magnitude/difference of signature enrichment between high and low velocity regimes. It is probable that irradiance acts as an interactive affecter on d13C by 1) increase in photosynthetic rate, and thus carbon demand, accentuating overall carbon limitation and decreased isotopic discrimination at low water velocities; and 2) increased utilization of d13C-enriched bicarbonate as a carbon source for photosynthesis with higher irradiance, contributing to overall signature enrichment. A field study examined in situ effects of water velocity and irradiance on d13C of Cladophora spp. and Spirogyra spp.; algal filaments growing in similar microhabitats varying in water velocity and canopy coverage were sampled and analyzed, but no correlations were found between water velocity or irradiance and d13C. Lack of in situ support for trends observed in controlled experiments are likely attributable to very limited field sample sizes, myriad confounding and noisy factors of dynamic environmental systems, and lack of precision (to-species identification) in algal taxonomic identification.
Dana Powell, Wesleyan University
Mentor: Dr. Melanie Gunn, University of Michigan
“Distribution and Success of Native and Invasive Phragmites australis in Northern Michigan”
Phragmites australis, or common reed, is represented by several subspecies (haplotypes) in North America. The native haplotypes are important components of wetland ecosystems, while a non-native haplotype introduced in the nineteenth century has become an aggressive invader. The goals of this study were to characterize the native and invasive haplotype distribution of Phragmites in northern Michigan, to determine which environmental characteristic are correlated with native, invasive, and overall Phragmites success, and to analyze the trends so that local potential predictors of Phragmites variable distribution and success might be identified. Fourteen wetlands were surveyed for native and invasive Phragmites stands. Ten native and four invasive stands were sampled. Environmental variables (including temperature, pH, proximity to human development, surface moisture, water conductivity and DO) and variables related to Phragmites success (stand area and density, height and diameter of the tallest stem, and leaf litter depth) were measured. In addition, each Phragmites site was paired to a similar site with no Phragmites. The data was compared for native, invasive, and control sites using paired T-tests and regressions. Temperature, human development, and, to some extent, water pH were found to be significantly linked to Phragmites haplotype variable distribution and success. Despite the limitation of small sample size, these early trends could be of particular relevance for land managers working to protect wetlands and slow invasive success. Among the environmental characteristic variables, temperature measurements resulted in the most comparisons with significance. Increased temperature seems to be linked to increased invasive success and decreased native success, with potential implications regarding the affects of climate change on wetlands in northern Michigan.
Jeffrey Price, Washington State University
Mentor: Nancy Tuchman, Loyola University Chicago
“A Mesocosm Experiment to Test the Effects of Typha x glauca Invasion”
Typha x glauca is a wetland emergent plant that has ivaded Great Lakes region wetlands. The goal of this study is to explain the mechanisms through which Typha x glauca comes to dominate the pant community. We used a mesocosm experiment to examine the influences of Typha and its litter on native plant community and soil nutrient dynamics in the Cheboygan Marsh, Cheboygan, Michigan. Based on previous research, it appears that the increase in above ground biomass, litter mass, total soil inorganic nitrogen and other factors, from the native to Typha zones may be the effects of Typha invasion. The results of the mesocosm experiment suggest that the effects of Typha invasion are due to two main mechanisms: out competition for resources and suppression of native plant growth by Typha litter accumulation. These data provide valuable information about the individual effects of each mechanism, allowing us to untangle confounding variables observed at Cheboygan Marsh.
Danielle Stoermer, St. Olaf College
Mentor: Dr. Troy Keller, Columbus State University
“Effect of Zebra Mussels (Driessena polymorpha) on Trophic State in Northern Michigan”
Zebra mussels (Driessena polymorpha) cause significant damage to the environment, most noticeably by reducing plankton densities and increasing water clarity, both of which indicate a reduction in trophic state. The Trophic State Index can be used to quantify changes in lake trophic state due to zebra mussels. This study examined the effect of zebra mussels on trophic state over time, and how lake morphometry influences the effect zebra mussels have on trophic state. Current trophic state data in the form of Secchi disk transparency, chlorophyll-a, and total phosphorous were collected at six lakes in northern lower Michigan. Sites were paired in each lake according to depth (shallow and deep). Historic data were collected in order to compare trophic state over time. No significant differences in any of the trophic state parameters were found between the pairs nor over time. This unique deviation from what is expected suggests that there are several different factors affecting how zebra mussels effect trophic state, such as lake size, pre-zebra mussel trophic state, and zebra mussel density. This has major implications for management, because a change in trophic state is undetectable in these lakes but zebra mussels are still affecting the lake ecosystem.
Christine Trac, University of Washington
Mentors: Drs. Brian Lamb and Shelley Pressley, Washington State University
“Influence of Soil Moisture on Isoprene Emissions From a Northern Mixed Hardwood Forest”
The objective of this study was to identify a relationship between soil moisture and isoprene emissions and treat the variables in a manner that could be compared with the Model of Emissions for Gases and Aerosols in Nature model’s (MEGAN) treatment of changes in soil moisture as a factor affecting emissions of isoprene. Soil moisture data and isoprene flux measurements from a northern mixed hardwood forest in northern Michigan were studied for the 2000-2005 growing seasons. The two variables were examined using the parameters from the MEGAN model where soil moisture emission activity factors, calculated from observed soil moisture measurement data, were compared to observed isoprene fluxes normalized for photosynthetic photon flux density, temperature, and light. Variability in the trends was observed between the individual years showing positive, negative and no relationships. The results demonstrate that there is no relationship between soil moisture and isoprene emissions.
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