Ben Dickinson

Adaptive Cluster Sampling for Freshwater Mussels in the St. Croix River

The United States has an incredibly diverse population of freshwater mussels, many of which are critically endangered. Estimating population and habitat characteristics for freshwater mussels is challenging due to the difficulty of underwater sampling and because of spatial distribution patterns. The St. Croix River has several state and federally endangered mussels, including the federally endangered Quadrula fragosa and Lamsilis higginsii, as well as the state endangered Cyclonais tuberculata. In this study we tested a new design for sampling these mussels more effectively and efficiently. We developed a modified two-stage stratified adaptive cluster sampling (ACS) technique in the St. Croix River to efficiently sample these rare, spatially aggregated mussels.

In 2005 we collected 750 mussels at Franconia, Minnesota, including target species from three of 10 50-m2 high-density cells. Of the target species, we found 6 Cyclonaias tuberculata (0.8% of the population), 2 Quadrula fragosa (0.27%) and 3 Lampsilis higginsii (0.4%). Four of these individuals were collected from one adaptive cluster.

In 2006 we applied the sampling technique at Interstate State Park, Minnesota. This area has much higher mussel density than found at Franconia, with 19 mussels per square meter being considered ?high density?. We collected 3177 total mussels, 194 Cyclonaias tuberculata (6.1% of total population), 6 Lampsilis higginsii (0.19%), and 15 Quadrula fragosa (0.47%). Ten of the 15 Quadrula fragosa were in clusters, as well as four of the six Lamsilis higginsii, indicating that these rare mussels are often spatially clustered, and ACS may be an effective way to find these clusters.

Water discharge and Sediment Flux Measurements in the Proglacial Zone of a Cirque Glacier: West Washmawapta/Helmet Mountain Glacier, British Columbia

Field measurements of cirque glacier dynamics can provide constraints on rates of subglacial erosion; measurements of suspended and bedload sediment in proglacial streams are relevant for quantifying supraglacial and subglacial transport. If the rates of headwall backwearing are known, sediment transport in streams can be used to determine subglacial erosion.

Stream gages were installed at two locations along the complex proglacial stream network, which included meltwater from an adjacent glacier, several streams exiting the glacier terminus, and at least 4 small lake basins.  Stream gages collected stage and pressure data, conductivity, water temperature, and water turbidity every 15 minutes between June 1 and September 9.  Stage measurements at the stream gages were constrained using both salt as a conservative tracer and a price meter to construct a discharge rating curve. Conductivity and water temperature analysis determined lag time within the subglacial hydraulic system.  Water samples at the stream gages in conjunction with turbidity measurements provide a rating curve for suspended sediment. Additional samples throughout the water column and bedload samples constrain the total sediment discharge from the system allowing us to better quantify subglacial and basin sediment storage .

Long-term monitoring of freshwater mussels of Franconia and Wild River Stae Park, St. Croix River

Freshwater mussels are long-lived, sedentary animals that filter feed and are often used as indicators of water quality.  Degradation of aquatic habitats has caused a decline in freshwater mussel densities since the late 1800s. Of the 48 species native to Minnesota, 25 are listed as endangered, threatened, or of special concern.  Few studies have been done on these animals, especially on such a broad scale, where trends become more apparent.  This study was conducted to monitor the changes in freshwater mussel populations on a long-term scale in the St. Croix River.  At Franconia and Wild River, sites along the St. Croix River, mussels were collected from 100 0.25 m2 quadrats at each site, identified and measured.  Data on water flow and riverbed substrate composition were also collected.  Since previous data collection (2003) no significant change in sediment composition was discovered.  The most abundant species at Franconia, Truncilla truncata, continues to decline as the dominant species with an increase in the relative abundance of Actinonaias ligamentina. The mussel assemblage structure has remained fairly constant at Wild River. Mussel densities appear to be relatively consistent with past assessments at both locations.

Long-term monitoring of freshwater mussels of Franconia and Wild River Stae Park, St. Croix River

Freshwater mussels are long-lived, sedentary animals that filter feed and are often used as indicators of water quality.  Degradation of aquatic habitats has caused a decline in freshwater mussel densities since the late 1800s. Of the 48 species native to Minnesota, 25 are listed as endangered, threatened, or of special concern.  Few studies have been done on these animals, especially on such a broad scale, where trends become more apparent.  This study was conducted to monitor the changes in freshwater mussel populations on a long-term scale in the St. Croix River.  At Franconia and Wild River, sites along the St. Croix River, mussels were collected from 100 0.25 m2 quadrats at each site, identified and measured.  Data on water flow and riverbed substrate composition were also collected.  Since previous data collection (2003) no significant change in sediment composition was discovered.  The most abundant species at Franconia, Truncilla truncata, continues to decline as the dominant species with an increase in the relative abundance of Actinonaias ligamentina. The mussel assemblage structure has remained fairly constant at Wild River. Mussel densities appear to be relatively consistent with past assessments at both locations.

Synthetic Progress Towards a Novel C3 Symmetric Macrocycle

Ostensibly triangular in overall shape, the desired target molecules of this project will feature a high degree of shape persistence, along with physical properties that may ultimately find application to materials science.  In the course of synthesizing the target molecules, we expect to learn about existing, and/or develop new, synthetic protocols that may be of general utility to others.

Investigating Quantum Wells

Quantum wells are semiconductor structures, which are so small that the energy levels of electrons in the wells are quantized, as in atoms. Quantum wells are important to study because they can be used to build lasers or high-speed transistors. We investigated a quantum well with a parabolic confining potential (a parabolic quantum well) designed to have equally spaced energy levels, 0.01 eV apart.  When the samples are excited with a femtosecond laser pulse, the excited electrons emit terahertz frequency electromagnetic radiation at a frequency determined by the level spacing. By studying the THz radiation produced, we learned about the physical characteristics of our sample and how radiation is emitted.  There are two theories of how THz radiation is generated: quantum beating and ultrafast field screening.  Through our experiments, we found our results supported the quantum beating theory.

Dioxirane Decomposition: Computational Analysis Using the B3LYP and Complete Basis Set Methods

Starting with the dioxirane formed by the ozonolysis of cyclopropene, we can use quantum computational chemistry to further investigate the decomposition pathway.  The dioxirane decomposes to form both carboxylic acid and diradical species, with evidence that carbon dioxide (paired with acetaldehyde) and a vinoxy radical (along with a formyloxy species) will also be produced.  Calculations utilizing B3LYP hybrid theory and Complete Basis Set (CBS) method can be used to accurately characterize these products and pathways.

Habitat and Landscape Impacts on the Wetland Bird Community in East Central Minnesota

Wetlands provide important breeding and foraging habitat for many birds. There are many wetland habitat characteristics that affect wetland bird habitats, including wetland size and shape, structure of wetland plant communities, surrounding habitat characteristics, and nest predation rates. We surveyed birds, measured nest predation rates, and sampled vegetation in 12 wetland sites over a period of 1 month. Our results indicate that development and loss of structural diversity are strongly correlated with increased bird species richness and decreased bird species diversity. 

Habitat and Landscape Impacts on the Wetland Bird Community in East Central Minnesota

Wetlands provide important breeding and foraging habitat for many birds. There are many wetland habitat characteristics that affect wetland bird habitats, including wetland size and shape, structure of wetland plant communities, surrounding habitat characteristics, and nest predation rates. We surveyed birds, measured nest predation rates, and sampled vegetation in 12 wetland sites over a period of 1 month. Our results indicate that development and loss of structural diversity are strongly correlated with increased bird species richness and decreased bird species diversity.   

Using High Resolution Laser Spectroscopy to Determine the Electronic Structure of TaO

We have recorded hyperfine resolved laser excitation spectra of the B2F5/2 –X12D3/2 and C2D 3/2 –X12D3/2 electronic transitions of TaO.  The electronic spectrum of this molecule was first explored by Cheetam and Barrow using a grating spectrograph. A Ti:sapphire ring laser was used to analyze TaO molecules that were produced with a hollow cathode discharge. We achieved hyperfine resolution using the sub-Doppler technique of inter-modulated florescence spectroscopy. A least-squares fit of the transition frequencies was used to determine improved values for the rotational parameters and values for the magnetic dipole and electric quadrupole parameters of these states. Our results are summarized in the following table:

Infrared Spectroscopy of a-Ge:H Thin Films

The goal of this project is to determine the hydrogen concentration and microstructure of hydrogenated amorphous germanium (a-Ge:H) thin films. To this end, we analyze the infrared transmission spectra of these films. By modeling the interference in the thin film and the substrate, it is possible to determine absorption regions in the film. We estimate the absorption at the three wavenumbers of interest (565, 1880, 1980cm-1) by fitting the spectral peaks with Gaussian functions. From this, we ultimately find the integrated hydrogen absorption in the films and calculate the microstructure parameter R.

Optimizing Electrical Properties of a-Ge:H Thin Films

Amorphous hydrogenated germanium (a-Ge:H) is one of several semiconductor materials used as the absorbing layer in solar cells. The basic function of a solar cell is to absorb photons and convert this energy into electric current.

The main goal of our project is to optimize the conditions with which these thin films semiconductors are grown. In these initial studies we are varying hydrogen gas partial pressure and substrate temperature to determine the effect of these parameters on the conductive properties of the films.

McKay Tantalizer Algebras

Via a classical construction, we associate a family of algebras {CkG} to each finite subgroup G of the special unitary group SU2. These algebras have beautiful combinatorics vis-à-vis walks on their associated Dynkin diagram or McKay quiver. The construction works like this: Let V = C2 be the natural two-dimensional representation of SU2 given by usual matrix-vector multiplication and let V⊗k be its k-fold tensor product. Then for any subgroup G ⊆ SU2, we let CkG be the algebra of transformations on V⊗k that commute with G — that is, the tensor power centralizer algebra (or “tantalizer”) of G. We prove that the dimension of G equals the number of closed walks of length 2k on the Dynkin diagram. The finite subgroups of SU2 reduce (in a concrete way) to two infinite classes — the cyclic groups of order m and the dicyclic groups of order 4m — and three exceptional cases, the binary polyhedral groups. In all but the exceptional cases, we have a bijection between a basis of CkG and these walks, and we have strong conjectures about the general structure of these algebras.