Award Recipients
The Faculty and Graduate Student Researcher recipients of the 2009-10 FIRMS Stable Isotope Science
Michael Bell, Ph.D. Candidate, Botany & Plant Sciences
Advisor: Edith Allen, Botany & Plant Sciences
Determining the source of anthropogenic atmospheric nitrogen pollution through the use of dual stable isotopic analysis
Abstract
Anthropogenic nitrogen deposition has become a global problem due to increased use of fertilizers in agricultural regions and N emissions from industry and internal combustion engines. Deposition rates within the Los Angeles air basin are exceedingly high and are influencing the Coachella Valley desert ecosystem to the east. Desert productivity tends to be limited by moisture and nitrogen availability which both increase during seasonal pulses of precipitation. It is currently unclear what percentage of deposition within the Coachella Valley is being transported from Los Angeles and what percentage comes from local sources. Stable nitrogen isotopes in NO3- and NH4+ can be used to help distinguish the sources that contribute to atmospheric nitrogen deposition. Nitrogen molecules created through anthropogenic processes tend to have an isotopic signature different than those created through natural reactions. The proposed research is designed to help improve air quality in the Coachella Valley and Joshua Tree National Park by understanding sources of pollution. Air, soil, and vegetation samples have been collected from sites located throughout the valley and will be analyzed for both δ15N and δ18O. The change in concentrations of the isotopes over space and time will be used to determine where the anthropogenic nitrogen is originating. Changes in soil values will be used to determine what percentage of deposited nitrogen remains available in the rhizosphere and how much is leached from the upper soil profile. Vegetation samples will be compared with air and soil values to determine if a local species can be used as a bioindicator for deposition.
Jennifer Henke, Ph.D. Candidate, Entomology
Advisor: William Walton, Entomology
Determination of wetland macroinvertebrate food webs across a gradient of nitrogen enrichment
Abstract
In southern California and throughout the world, wetlands created for wastewater treatment or to mitigate wetland losses are increasingly common. Although mitigation wetlands do not treat highly nutrient-enriched municipal or agricultural wastewaters, many of these wetlands do receive nutrient-laden runoff from adjacent urban and suburban areas. While we know that many mitigation wetlands do not serve the same ecological function as the natural wetlands that they replace, we know surprisingly little about the ecological interactions taking place within these wetlands. Insects within wetlands are important links in the transfer of energy and nutrients within food webs. While stream insects can be classified into feeding groups based on specialized mouthparts, wetland insects are typically classified as either predators or non-predators due a lack of specialized feeding structures. Non-predators are considered omnivores, feeding on algae, bacteria, fungi, and plant detritus. I will use stable isotope analysis to examine how nutrient input affects the food web structure in replicate experimental wetlands subjected to different levels of nitrogen enrichment. Stable isotope studies should be especially informative to describe the resource use by organisms in wetland food webs and to assess the strength of bottom-up enrichment effects across the trophic structure of wetland insect communities. I will also assess changes in insect species diversity, abundance, and secondary production across the gradient of nitrogen enrichment.
Paul Koster, Ph.D. Student, Environmental Sciences
Advisor: James Sickman, Environmental Sciences
Assessment of food web recovery from fish introductions using stable isotopes: Sierra Nevada, California
Abstract
Over the last century nearly all lakes in the Sierra Nevada were stocked with non-native species of trout. Stocking resulted in shifts towards dominance of smaller zooplankton and benthic macroinvertebrate species and extirpation of several amphibian species including the endangered mountain yellow-legged frog (Rana muscosa). Previous studies documented the loss and subsequent recovery of two large zooplankton species, H. shosone and D. melanica. However, attempts to reintroduce Rana muscosa to now fishless lakes were not completely successful. One question remains: Have the foodwebs of lakes where fish were removed returned to their pre-introduction structure or has a new fishless food web developed? One way to assess changes in food webs through time is to measure stable isotope distributions within an ecosystem. Stable isotope ratios of nitrogen and carbon can be used to elucidate food web structure as well as infer animal diets. My isotope analyses will focus on two lakes containing fish and two lakes where non-native trout were removed in 1996. Isotope measurements will be conducted on the dominant invertebrate and zooplankton species common to both fish and fishless lakes and tissues from trout and frogs. Samples will be analyzed from 1998, 2001, 2005, 2007, and 2010 anticipating that food web changes will be greatest immediately following the fish removal and will diminish as time progresses. The biological samples I will use were preserved in ethanol. Previous research indicates preservatives can alter the isotopic composition of the organisms, however if this limitation can be overcome, then previously collected samples can be used to examine food web changes through time. In order to minimize the affect of prior preservation methods, I will test the efficacy of DIW rinsing for my isotope samples. The samples will undergo a series of DIW soaks and rinses over 5 days in order to reduce the effects of the preservative on the final isotope composition of the samples.
The Faculty and Graduate Student Researcher recipients of the 2009-10 Mini-Proposal Shipley-Skinner Reserve- Riverside County Endowment
Michelle Murphy, Graduate Student Researcher, Biology
Advisor: Michael Allen, Plant Pathology & Biology
Evaluating Wildlife Corridor Linkages: Do Underpasses Connect the Peninsular and Transverse Mountain Ranges?
Abstract
Wildlife corridors can be critical conservation design components for sustaining biodiversity in increasingly fragmented landscapes, ensuring a means for species to disperse, track preferred habitat conditions in a dynamic environment and to facilitate genetic heterogeneity between populations. Highway underpasses provide a means for wildlife to make safe crossings between suitable habitats in areas where man-made barriers, such as railways and high-speed highways, may be impeding wildlife movement. However, there are almost no critical studies demonstrating the degree to which such corridor structures are actually used by wildlife in desert environments. My project focuses on documenting the use of highway underpasses by wildlife at what has been identified as a critical wildlife linkage between the Peninsular and Transverse mountain ranges of southern California to determine whether (1) animals preferentially use available underpasses to navigate from one side of this barrier to the other; and (2) animals preferentially use dry washes as movement corridors between the mountain ranges and are therefore more likely to encounter an underpass which they can utilize at the highway barrier. I will implement the use of sooted-aluminum track-plate stations and infrared motion detection cameras to detect wildlife presence within the underpasses, dry washes, and throughout the desert matrix. I will also conduct road mortality surveys to record occurrences and locations of animal road kill which I will then use to determine if these occurrences are correlated with the absence of available underpass structures. I expect to use these results as pilot data for planning and implementing a more expansive study to identify generalized principles for effective corridor design in arid environments.
Kai Palenscar, Graduate Student Researcher
Community Factors Affecting Giant Reed (Arundo donax) Establishment within the Riparian Plant Community of Southern California
Abstract
Giant reed (Arundo donax L.) is a large C3 grass that invades riparian plant communities in coastal areas of the United States from California to Maryland. My dissertation research focuses on ecology and environmental responses of giant reed and native riparian species, and the application of this knowledge to develop management strategies using native plant competition as a form of cultural control. Research in the Holt lab has shown that competitive native riparian species can suppress establishment of giant reed. Current research by the USDA is testing insect biocontrol agents from Europe on giant reed populations in Texas. However, no work has been conducted on rodent herbivory, which has been observed in natural populations of giant reed in California and may be an important factor in controlling ramet survival and clone fecundity. This project investigates the success of giant reed establishment in existing riparian plant communities of southern California and the impact of rodent herbivores on this establishment process. It is predicted that giant reed establishment will be inhibited by native evergreen riparian species, whereas deciduous species will allow for establishment over a 12 month growing period, and that natural herbivory will negatively affect giant reed establishment regardless of native plant community composition.
Lynn (Wihbey) Sweet, Graduate Student Researcher, Botany & Plant Sciences
Advisor: Jodie S. Holt, Botany and Plant Sciences
Environmental and Community Factors Influencing the Distribution of Pennisetum setaceum in California
Abstract
African fountain grass (Pennisetum setaceum) is invasive outside its native range and is now spreading in wildlands in Hawaii, Arizona and California. While fountain grass is increasing in California, its potential range and impacts on local communities have not been determined. The use of a climate-matching model to predict potential for spread of fountain grass in California showed that areas that support coastal sage scrub (CSS) communities are climatologically favorable for fountain grass. Model results are being further refined to include other factors such as soil, slope and aspect. Preliminary analysis of 2009 vegetation data from transects in 3 counties in southern California showed a measured decline in native species richness in plots with high fountain grass cover. Repeated sampling in 2010 will strengthen the dataset in order to make recommendations to land managers regarding impacts of fountain grass in southern California.
Kristin Weathers, Graduate Student Researcher, Botany & Plant Sciences
Advisor: Edith Allen, Botany and Plant Sciences
Thresholds for exotic forb control to restore coastal sage scrub vegetation in California
Abstract
Many damaged ecosystems do not recover after a management action. This suggests that restoration thresholds, or barriers, exist that prevent the system from returning to a less degraded state. Identifying these thresholds helps to prioritize management activities , as well as improve restoration success. The coastal sage scrub plant community (CSS) is being widely replaced by thick stands of invasive annual grasses. Studies have documented that when the cover of exotic grasses is removed, establishment of the native shrubs species fails to occur, even with the addition of seed. Native forbs return, but in lesser proportions than exotic annual forbs of the genus Erodium. Our objectives are to test whether high densities of exotic forbs in the genus Erodium act as a constraint on restoration of the coastal sage scrub community and, if so, to identify density thresholds where significant reductions in the establishment of native species occur. Two experiments will be initiated. In the additive competition seeding experiment seven densities of Erodium cicutarium will be seeded with a single density of one of two natives, a native annual forb, Cryptantha intermedia, a native shrub, Artemisia californica. The second is a removal experiment at a northeastern San Diego County Park burned by wildfire in 2003, following which dense stands of Erodium botrys became established. Erodium botrys will be removed from the plots by hand in order to establish same 7 different Erodium density treatments as in the first experiment. Half of these plot will be seeded with Cryptantha and the other half with Artemisia. For both experiments the density and percent cover of Erodium and of native plants in each plot will be determined at the peak of the growing season. The response of the native species will be measured so that a regression of response of native emergence and growth based on Erodium density can be calculated.