Research Experiences for Undergraduates (REU)
in Integrated Environmental Sciences

Christian G. Andresen, University of Texas at El Paso
Molecular genetic analysis of picoeukaryotic communities along an Estuarine gradient
Christian G. Andresen examined the diversity of picoeukaryotic communities along an estuarine gradient using molecular techniques. Picoeukaryotes are responsible for a significant fraction of the primary production in both marine and freshwater ecosystems. Their small size and cryptic morphology have led to the use of DNA-based analytical methods. Christian used Restriction Fragment Length Polymorphism (RFLP) fingerprinting of a fragment of the 18s rDNA gene to assess the diversity of picoeukaryote communities. He found that three Picoeukaryotic communities, collected along an estuarine gradient, were all remarkably diverse, which is consistent with results from other aquatic environments. The great diversity suggests that particular picoeukaryotes adapt to particular conditions along the estuarine gradient. This study provides essential baseline information for further studies of picoeukaryotic communities in estuarine environments and necessary data for subsequent sequence analyses of the clone libraries, generating further insight and resolution into the genetic structure of picoeukaryote communities.
Supervisor: Deana Erdner, Phytoplankton ecology, Marine Science Institute

Dawne Ballard, Bryn Mawr College
Carbon Storage on the UT Campus – How Landscaping Choices Affect Soil Organic Carbon
Finding ways to maximize carbon storage at the local scale is becoming increasingly important as humans continue to add carbon dioxide to the atmosphere and temperatures continue to rise globally. In urban environments, there is the potential to increase storage of organic carbon in soil by selecting landscapes with a greater capacity to sequester carbon.

To begin addressing this issue, Dawne asked how the amount of soil organic carbon (SOC) stored in soils varied across managed landscapes in an urban campus setting. Dawne analyzed SOC in soils from the UT-Austin main campus, where typical examples of many city landscapes can be found. These included lawns, annual and perennial beds, as well as areas that are not landscaped or disturbed.

Results showed that SOC varied significantly across landscape types. Soils in landscaped beds contained more organic carbon, while weedy unlandscaped areas and the prairie had lower levels. The SOC stored in lawns was intermediate between the beds and unlandscaped areas. Total inorganic nitrogen in soil did not differ significantly by landscape type, though nitrate tended to be higher in lawns and carbon was higher in woody perennial beds. Currently, landscaping across the main UT Austin campus is heavily dominated by lawns, and thus these contain the majority of soil organic carbon.

Our choices of landscaping in urban settings can affect the amount of organic carbon stored in soils by as much as 191%. Based on this initial data set for SOC on the UT Austin campus, landscapes could be managed to increase soil carbon storage. Because beds contain on average 29% more organic carbon on a per gram basis, an increase in area of campus covered by beds would lead to an increase in carbon stored. The natural streamside habitat, which makes up 35% of the campus environment that was sampled, contains more organic carbon than any of the managed habitats. Thus, aside from adding more landscaped beds, another potential way to increase carbon storage on the UT campus may be to increase the number of natural habitats. Following the newly planted prairie over time will allow us to test this idea.
Supervisor: Christine Hawkes, Section of Integrative Biology

Andrew Brouwer, SUNY Postdam
Wind Controlled Hypoxia and Stratification in Corpus Christi Bay
Andrew Brouwer investigated hypoxia, or oxygen deficiency, in Corpus Christi Bay, a wide, shallow bay on the Texas Gulf Coast. Hypoxia is episodic on the bottom of Corpus Christi Bay in the late summer months; it can be a significant stressor for benthic communities, and a prolonged period of hypoxia is deadly for many organisms. Andrew began by developing of a method of more easily analyzing field data using MATLAB. He then worked to analyze a data set from the previous year, paying particular attention to salinity, dissolved oxygen, and temperature. His analysis painted a picture of a system in which hypoxia episodes begin with a high wind event and are also eventually mixed by the wind. To round out his experience with a little field work, Andrew participated in a data collection trip to Corpus Christi Bay. Andrew’s work fits into a larger picture that will eventually allow us to predict hypoxia and take measures to minimize human impact on benthic communities.
Supervisor: Ben R. Hodges, Department of Civil Engineering

Stephanie Diaz, California State University, Fullerton
Nitrate Dynamics in the Mission and Aransas Rivers Following a Major Storm Event Watershed export events are important in understanding nutrient transport and processing in estuarine ecosystems. In southern Texas, a high percentage of annual nutrient export may occur during a few major storm events. Predictions have been made suggesting that future warming will increase the frequency and intensity of precipitation, storms, and tropical cyclones. In addition to increased storm events, changes in land use and/or land cover (LULC) in watersheds may lead to significant changes in nutrient input to estuarine ecosystems. In order to improve our understanding of nitrogen sources to Copano Bay during storm events, concentrations and N isotope values of NO3- in the Mission and Aransas rivers were measured during and after a major storm event in July 2007. Water samples were collected at three sites within the Mission and Aransas watersheds, each draining areas with different LULC characteristics. Isotopic analysis of NO3- was carried out using an ammonia diffusion method adapted from Sigman et al. (1997). Nitrate concentrations and N isotope values were similar at all sites during the peak of the storm event, indicating rainwater nitrate as an ubiquitous N source. A major increase in NO3- concentration and delta¹⁵N at the upper Aransas site as the storm water receded indicated a shift to an anthropogenic NO3- source. At the same time a much smaller increase in delta¹⁵N at the upper Mission and lower Aransas sites was consistent with a shift from rainwater NO3- to natural soil NO3-. These preliminary data are helping to characterize nutrient loads from the Mission and Aransas rivers to Copano Bay in order to provide a strong foundation for future projects in the Mission-Aransas National Estuarine Research Reserve (MANERR).
Supervisor: James W. McClelland, Marine Science Institute

Ashley Francis, Baylor University
Tracing Urbanization through Streamwater Chemistry Recorded in Tree Rings Increasing urbanization is adversely affecting watersheds and causing the significant decline of streamwater quality. In the Austin, Texas area higher levels of anthropogenic influences on streamwater correlate with increasing isotopic strontium composition. The isotopic composition of strontium, expressed as the ⁸⁷Sr/⁸⁶Sr ratio, within streamwater can potentially be recorded in annual tree rings due to the process of some trees, such as the bald cypress, placing roots in nearby streams to consume water. It is predicted that as urbanization increases over time, ⁸⁷Sr/⁸⁶Sr will also increase chronologically within tree rings. Strontium is an effective tracer in trees because, unlike chemical concentrations and light stable isotope ratios, ⁸⁷Sr/⁸⁶Sr is not fractionated by physiological processes carried out by trees (Cooke, 2005). Instead, since ⁸⁷Sr/⁸⁶Sr is a heavier element, it is controlled by influences within the tree’s environment (Cooke, 2005). After analyzing the ⁸⁷Sr/⁸⁶Sr of a bald cypress tree about 80 years old, the streamside trunk core ⁸⁷Sr/⁸⁶Sr gradually increased towards the ⁸⁷Sr/⁸⁶Sr of streamwater. In contrast the bankside trunk core ⁸⁷Sr/⁸⁶Sr moderately declined towards the ⁸⁷Sr/⁸⁶Sr of limestone instead of the ⁸⁷Sr/⁸⁶Sr of the surrounding soil. These results indicate that fluctuations in streamwater ⁸⁷Sr/⁸⁶Sr can be traced by trees over time, ultimately revealing the predicted steady increase in ⁸⁷Sr/⁸⁶Sr within the years that urbanization began to affect streamwater quality. If tree rings can indicate when urbanization initially began to affect streamwater quality, by displaying increasing ⁸⁷Sr/⁸⁶Sr ratios, then in the future we can prevent the levels of urbanization that degrade streamwater quality.
Supervisor: Supervisor: Jay Banner, Department of Geological Sciences

Laura Merner, Clark University
Assessing Potential for Hyporheic Exchange at Hornsby Bend Island, Colorado River TX and Waller Creek TX
The intent of this study is to further understand surface-ground water interactions at Hornsby Bend Island (HBI) and Waller Creek (WC) in Austin, Tx by collecting preliminary data regarding the hyporheic zones at each site. Hyporheic zones, regions within stream sediments and banks where surface and ground water interact, play critical roles in hydrologic, biogeochemical, and ecologic processes occurring in rivers and aquifers. Hyporheic exchange can be estimated by analyzing grain size, porosity and calculating hydraulic conductivity (or permeability) of sediment samples. In this study we sampled the sediments at 5 sites in Hornsby Bend Island and established 8 sampling transects across Waller Creek. After grain size analyses of the samples, empirical equations were used to calculate hydraulic conductivity. It was found that: 1) Grain size varies drastically throughout the island at all layers of the sediment. However, despite changes in permeability at the surface, hydraulic conductivity of subsurface sediments at Waller Creek are reasonably uniform, 2) Sediments preferentially deposit near pilings, large woody debris piles and bends in rivers. Hyporheic zones will tend to be present in these areas as well. This trend of preferential deposition is largely responsible for considerable changes in hydraulic conductivity along a single transect of Waller Creek, 3) Hornsby Bend Island appears to have an armored layer on the surface at site 5 which would decrease surface permeability, however empirical formulas do not show this.
Supervisor: Bayani Cardenas, Department of Geological Sciences

Dawn Saepia, Cornell University
The influence of soil heterogeneity and water table fluctuations on sulfate concentration variation in groundwater at Monticello lignite mine, Northeast Texas
Dawn Saepia addressed the temporal and spatial sulfate concentration fluctuation at Monticello lignite mine, Titus County. During strip mining, overburden is deposited to form a heterogeneous spoil material of un-mined silt, silty-sand, and mud facies. Reclamation restores the land, but with changed hydrogeologic properties. Water table levels were mapped using ArcGIS. Overburden wells located in water table depressions with high sulfate concentrations may indicate flushing of sulfate from the reclaimed sections. After dewatering during mining, the water table levels changed over time. This variation of water table level may indicate a change in groundwater flow. Heterogeneity of the spoil material was tested through X-Ray Diffraction (XRD) analysis of surface soil and groundwater filtered suspended sediment specimen. Qualitative mineralogical analysis showed quartz, kaolinite, and iron peaks which may indicate clay and sand mixing and the presence of iron sulfate. No significant amounts of gypsum or pyrite were identified through XRD. The absence of gypsum may indicate that the groundwater is undersaturated with respect to gypsum. Low-flow well purging was used to provide water quality parameters including conductivity, dissolved oxygen, temperature, and a pH fluctuating around 7.8. The determination of the specific cause of sulfate variation may help with the prevention of acid mine drainage.
Publication: Cagle, M.F., Sharp, J.M. Jr., Saepia, D.M., 2007, Controls of sulfate variability in groundwater at a lignite mine, Northeast Texas: Geo. Soc. America, Abs. with Programs (Ann. Mtg.), vol. 39, no. 3, p. 3
Supervisor: Jack M. Sharp, Department of Geological Sciences

Joyce D. Varela, King’s College
Between-population variation in a sexually selected character: opercular (ear) flap size in sunfish (L. megalotis and L. cyanellus)
Joyce D. Varela focused on how opercular ear flap size of male longear and green sunfish (Lepomis megalotis and Lepomis cyanellus) vary between populations. Understanding patterns of variation between populations is important in addressing 1) genetic variation, 2) differences in habitat quality, or 3) differences in sexual selection. Various species of male fish exhibit sexual characters, for example the opercular ear flap, as a mating signal to attract female mates. The opercular flap is a soft scaleless extension of the operculum that conceals the gills, and is longer in males than in females. To determine how opercular ear flap size varies between populations, Joyce analyzed digital photographs of two populations of longear sunfish and green sunfish from Waller Creek and Williamson Creek. She then measured their standard length (SL), body depth (BD), and opercular ear flap area using tps.Dig. She found that male longear sunfish and male green sunfish have bigger ear flaps in Waller Creek when compared to their conspecifics in Williamson, suggesting that these populations are divergent. This finding opens up future avenues of research into the causes of variation in sexually dimorphic traits, including possible variation in sexual selection due to different sex ratios, visual environment (e.g. turbidity), pollution (e.g., estrogens). The differences between populations also highlights the importance of considering genetic variation between populations in conservation schemes.
Supervisor: Daniel I. Bolnick, Section of Integrative Biology