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Environmental Studies Department
Olin Rice 249
1600 Grand Avenue
St. Paul, MN 55105
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St. Croix River Research Rendezvous 2009

On October 20, 2009, seven Macalester College students gave presentations at the St. Croix River Research Rendezvous.  The St. Croix Watershed Research Station of the Science Museum of Minnesota sponsors this meeting.  The student research was sponsored by faculty at Macalester College and staff of the National Park Service.

Historic Resources of the St. Croix Valley
Claire Vincent, Macalester College

The St Croix River valley has a diverse cultural history; from the Ojibwe to the Dutch to the Army Corps, every group impacted the valley differently. This PowerPoint presentation will provide an overview of the cultural and environmental history of the St. Croix, as well as an overview of valley-related archival resources at the Minnesota Historical Society (MHS). The resources of the MHS can help to support the research activities of scientists working in the valley. This presentation is the result of a partnership between Macalester College and MHS, supported by an endowment fund established by the James Taylor Dunn family to promote and preserve the history of the St. Croix River valley.

A DNA Barcoding Approach to Identifying Newly Transformed Juvenile Mussels Recovered From Naturally Infested Fishes
Sarah L. Boyer, Alex A. Howe, and Mark C. Hove, Biology Department, Macalester College, Saint Paul, MN

DNA barcoding is a method for species identification using a short stretch of mitochondrial DNA. We have developed a DNA barcoding approach to the identification of recently transformed freshwater juvenile mussels, which are in many cases impossible to identify to species using morphology alone. We have built reference sequence datasets for two mitochondrial genes from adult mussels of known identity, and successfully used our method to identify juveniles recovered from multiple species of naturally infested fishes in the St. Croix River.

We sequenced two mitochondrial loci: ND1 (NADH dehydrogenase subunit 1) and COI (cytochrome c oxidase subunit l). For 7 of the 40 unionid mussel species native to the St. Croix River, sequences from both loci were already publicly available on GenBank. For all mussels native to the St. Croix River without at least two sequences from different specimens for both genes, collection of mairtle tissue clips from adult mussels was performed in the St. Croix and upper Mississippi River. Using DNA extraction, PCR, and DNA sequencing, we were able to build a reference dataset for 37 of the 40 mussels in the St. Croix River.

Three species of fish were collected from the St. Croix and subsequently held in aquaria:  walleye, freshwater drum, and spotfin shiner. To ensure that mussels collected from the parasitized fish represented species that successfully metamorphose on the host species in question, as opposed to species that infest but do not metamorphose on the host, we waited for transformed juveniles to fall from the fish by natural means and collected them by siphoning aquaria, rather than attempting to excise them from the fish.  Juvenile mussels were photographed and DNA was extracted from each specimen, and we used PCR and DNA sequencing to generate sequences from our genetic loci of interest.

We successfully used phylogenetic analysis of sequences from adult and juvenile mussels to identify juveniles with a high degree of confidence. From the drum we identified Ellipsaria lineolata, Leptodea fragilis, and Potamilus ohioensis; from the spotfin shiner we identified Fusconaia flava and Pleurobema sintoxia, and from walleye we narrowed down the identification of juveniles to either Lampsilis higginsii or Actinonaias ligamentina.

The Three Rivers Center at Macalester College and the Minnesota Historical Society:  Developing a Workshop to Advance Collaboration Between Historians and Scientists
Dan Hornbach, Department of Environmental Studies, Macalester College, St. Paul MN
Lesley Kadish, Division of Library, Publications and Collections, Minnesota Historical Society, St. Paul MN

ln July 2007, the Andrew W. Mellon Foundation provided the funding to establish the Three Rivers Center (TRC) at Macalester College. One of the goals of the Center is to develop long-term partnerships with community groups, academic entities and government. One of the partnerships that have been developing is between the Center and the Minnesota Historical Society (MHS).

The MHS has a significant interest in the St. Croix watershed and an endowment fund, established by the James Taylor Dunn family to promote and preserve the history of the St. Croix River valley, has provided support for work related to the valley. The TRC likewise has an interest in the watershed through the research carried out by Professors Dan Hornbach (Biology) and Kelly MacGregor (Geology) in collaboration with the National Park Service. Given this congruence of interest, we have decided to focus the start of our collaborative efforts on the St. Croix.

ln addition to curriculum development that is being carried out, we thought we could advance conservation efforts on the St. Croix by exploring ways in which the resources of the MHS could help to support the research activities of scientists working in the valley. We are in the process of developing a workshop that would give St. Croix River researchers an introduction to the materials available from the MHS on the St. Croix. We also hope to gain an understanding from researchers what their major research questions are and how the MHS might best make information and materials available to them.

We are hoping to present this workshop in late February or early March 2010. At the October St. Croix Research Rendezvous, we hope to gather ideas from the participants about what topics will be of most interest to St. Croix researchers.

Resource Partitioning Among Freshwater Mussels
Cara Weggler. Environmental Studies Department, Macalester College, St. Paul, MN
Daniel Hornbach, Environmental Studies and Biology Departments, Macalester College, St. Paul, MN
Kelly MacGregor, Geology  Department, Macalester College, St. Paul, MN
Mark C. Hove, Biology Department, Macalester College, St. Paul, MN

Studies have shown Bivalves, particularly mussels are an important part of freshwater ecosystems (Strayer et al. 2004, Vaughn, Nichols, & Spooner 2008). As benthic filter feeders, mussels help to complete the nutrient cycle within rivers by transferring the nutrients and energy in the water to the sediment. However due to their sedentary nature, mussels are particularly vulnerable to human activity like the impoundment of rivers and agricultural and urban runoff. Even though North America has the most freshwater mussel species in the world, 43% of the taxa are now extinct, endangered, or threatened (Hornbach et al. 1996). Therefore in order to help conserve freshwater mussels species and also freshwater ecosystems it is important to investigate mussels and their interaction within the aquatic community (Vaughn, Nichols, & Spooner 2008). This study investigates whether mussels differ in habitat by examining sediment size, an indicator of sedimentation and quality of mussel habitat (Box & Mossa 1999). Six freshwater mussel species were analyzed: Actinonaias ligamentina (Mucket), Amblema plicata (Threeridge), Elliptio dilatata (Spike), Fusconaia flava (Wabash pigtoe), Quadrula pustulosa (Wartyback), and Truncilla truncata (Deertoe). Mussels and their surrounding sediment were quantitatively sampled at twelve sites along the St. Croix and Mississippi rivers. Sediment size was analyzed with the phi scale. Using ANOVA, three species (A. ligamentina, A. plicata, and E dilatata) were found to significantly differ by age in habitat preferences within species (p= .05, p= .03, p= .02). Using the Tukey's HSO test, significant differences in habitat were found among all juveniles (p i .OOO1) and adults (p< .00001). Although for two species, E. dilatata and A. ligamentina, there was no significant difference. Overall, results indicate mussels at least partially apportion habitat spaces by sediment size.


Box, J.B. & Mossa, J. (1999). "Sediment, land use, and freshwater mussels: prospects and problems, Journal of the North American Benthological Society." 18(l):99-1 1 7.

Hornbach, D., et al. (1990). "Factors lnfluencing the Distribution and Abundance of the Endangered Winged Mapleleaf Mussel Quadrula fragosa in the St. Croix River, Minnesota and Wisconsin." American Midland Naturalist. 136(2):278-286.

Strayer, D.L, et al. (2004). "Changing Perspectives on Pearly Mussels, North America's Most lmperiled Animals." Bioscience. 54(5): 429-439.

Vaughn, C.C., Nichols, S. J. & Spooner, D. E. (2008). "Community and Foodweb Ecology of Freshwater Mussels." Journal of the North American Benthological society. 27(2): 409-423.

Suspended Sediment and Organic Matter on the St. Croix River and Implications for Freshwater Mussels
Carl Skarbek, Environmental Studies Department, Macalester College, St. Paul, MN
Daniel Hornbach, Environmental Studies and Biology Departments, Macalester College, St. Paul, MN
Kelly MacGregor, Geology  Department, Macalester College, St. Paul, MN
Mark C. Hove, Biology Department, Macalester College, St. Paul, MN

A key characteristic of rivers is the ability to transport sediment and organic matter in the water column. Suspended sediment concentration can affect water quality and therefore benthic habitats, and plays an important role in river morphology. Understanding sources and sinks of sediment over annual to decadal timescales is relevant to quantifying environmental change along the St. Croix River, particularly in the region around the St. Croix Falls dam. Suspended organic material is important for the 40 species of freshwater mussels on the St. Croix River, as they are filter feeders and rely on organic sediment suspended in the water column to obtain nutrients. This project quantifies the flux of suspended sediment and organic matter in the river at four sites during the annual flow cycle. We are interested in the sources and sinks of suspended material between Nevers Dam and Franconia, and seek to understand factors controlling the entrainment and transport of suspended material. We also examine possible correlation between the amount of suspended organic material and mussel population density.

Since January 2008 water samples have been taken at four sites along the St. Croix River; Nevers Dam (above the top of the reservoir), National Park Headquarters (in the reservoir), the USGS gauging station (immediately below the dam), and Franconia (2.5 miles downstream from clam). Samples were collected every 1-2 weeks throughout the year. The samples were filtered, dried and weighed to determine total suspended solid (TSS) concentration. The filters were burned and weighed again to determine suspended sediment concentration (SSC), with the difference between TSS and SSC being the total organic content. Suspended organic concentration generally correlates with mean daily water discharge at all four sites, with peaks in the early spring and late summer. Organic material, likely made up of algae and microscopic particulates, makes up 30-60% of TSS at any given time. We calculated the total annual suspended sediment load at each site by calculating the sum of total grams of sediment flux per day (as determined by water discharge) for the entire year. Our calculations show that approximately 2500 metric tons of sediment per year is falling out of the water column and being deposited in the lndianhead Reservoir. This supports bathymetric and GIS analysis showing reservoir deposition exceeding 4 meters in parts of the reservoir over the past 40 years (Loeb and others, 2008). Sites with higher organic material in suspension have lower mussel density, but there was insufficient evidence for us to arrive at any causal relationship. Studies on bedload organic matter (closer to mussel habitat) in addition to TSS sampling at more sites could be useful determining possible trends.

Additional Reading:


Comparative Analysis of St. Croix River Mussels and Host Fish Species
Brandon Sansom, Washington and Jefferson College Department of Biology, Washington, PA
Mark C. Hove, Biology Department, Macalester College, St. Paul, MN
Daniel Hornbach, Environmental Studies and Biology Departments, Macalester College, St. Paul, MN

The parasitic relationship most North American freshwater mussels have with fish hosts is vital to their reproduction and dispersal, Female mussels release glochidia, microscopic larvae, into the water, often in ways that elicit fish to feed on or brush against them. Glochidia that encounter a suitable host have the ability to metamorphose into juveniles. Some mussel species rely on specific fish species as hosts, while others utilize a wide range of fish hosts. The objective of this research was to determine if variations in mussel population size are correlated to the fish host population size within the St. Croix River. Long-term mussel population data were obtained from Dan Hornbach and Macalester College Department of Biology. Fish population data were obtained from the Minnesota and Wisconsin Department of Natural Resources as well as the Minnesota Pollution Control Agency. The data were then analyzed using JMP 7.0 (SAS Institute). Comparison among all mussel species and all fish species revealed no strong trends. This was expected since there are 40 mussel species in the St. Croix River, each with different host requirements and host attraction strategies. The same held true when all species of juvenile mussel were compared to all fish species. However, strong trends were observed between mussel species with restricted host requirements and their specific fish host species. The strongest trend in the linkage between fish and mussel density was between Quadrula pustulosa (pimpleback) and Cyclonaias tuberculata (purple wartyback) mussels and their host, members of the catfish family. The pimpleback and purple wartyback peak density seem to have a lag period of three to five years relative to the peak catfish density. Four genera of mussels, Potamilus, Ellipsaria, Truncilla and Leptodea, and their host, the freshwater drum, had strong trends with a lag period of three to five years as well. These trends did not, however, produce any statistical significant results. The frequency of fish and mussel sampling are inconsistent, limiting our ability to accurately calculate lag periods. Additional fish survey data has recently been obtained and we hope to determine whether or not statistically significant trends exist.


McMahon, R. F. 1991. Mollusca: Bivalvia. Pages 315-399 in:Thorp, J. H. and A. P. Covich, editors. Ecology and classification of North American freshwater invertebrates. Academic Press, lnc., New York, NewYork.9 11 pp.

Strayer, D. L.2008. The Monster's Parts: Conservation lmplications. Page 118 in: Hauer, F. R. editor. Freshwater Mussel Ecology: A Multifactor Approach to distribution and Abundance. University of California, Berkeley, California. 204 pp.

Use of DNA Barcoding to Determine the Identity of Mussels Collected from Naturally Infested Freshwater Drum Fish Hosts
Nathan Juergens, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Sarah L. Boyer, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Mark C. Hove, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN

Many species of the Unionidae family of mussels have faced huge declines in numbers, with about 70% of the species listed as endangered, threatened or of special concern. They have a life cycle in which their larvae, called glochidia, parasitize fish by attaching to gills of the host.  To inform conservation management decisions, understanding which mussels parasitize which fish and where is important. However, glochidia are extremely difficult to tell apart by morphology alone because of their small size and similarities in appearance between species.

DNA barcoding is a relatively new alternative to standard morphological identification. This approach uses a database of standardized mitochondria DNA sequences. Sequences from new specimens can be compared back to the database for easy identification. During the Summer 2009 research season we sequenced DNA from frozen mussel samples available in the Biology Department at Macalester College, adding four Anodontoides ferussacianus sequences to an established database generated by our lab. We also did a detailed comparison of intra- and interspecific genetic distances for St. Croix mussel species.

We recovered glochidia from naturally parasitized freshwater drum in the St. Croix. To collect the fish specimens we went fishing several times in June 2009. Once we collected the fish we kept them in aquaria and allowed the juveniles to emerge naturally. We siphoned the bottoms of the tanks regularly to collect them. We sequenced the short mtDNA segments of the juveniles. The sequences from all of the juveniles were compared to the DNA barcoding database we had constructed. Using this method we were able to identify four juveniles from drum as Truncilla truncata and one juvenile as Potamilus ohioensis.

Sedimentation in the lndianhead Reservoir Behind St. Croix Falls Dam
Jacque Kitvirt, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Kelly MacGregor, Geology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Dan Hornbach, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Mark Hove, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Byron Karns, National Park Service, St. Croix Falls, Wl
Jill Medland, National Park Service, St. Croix Falls, Wl

The hydroelectric dam at St. Croix Falls was installed in 1904, impounding the upstream lndianhead Reservoir. Water velocity decreases as the river flows into the reservoir, allowing suspended sediment to settle and become trapped. ln addition, bed sediment transport is halted, cutting off source material for the region below the dam. Observations of bed sediment grain size suggest there has been a decrease in grain size of bed sediment at Interstate Park, just downstream of the dam, over the past 20 years (Hornbach and Hove, 2004).ln an effort to constrain sedimentation in the reservoir over the past century, and to assess changes in sedimentation rates across the lower portion of the reservoir, we collected sediment cores from three sites in lndianhead Reservoir in winter 2009.

The sediment cores have been examined at the LacCore Lab at the University of Minnesota. They have been (1) logged for density, (2) scanned for magnetic susceptibility, (3) imaged at high-resolution, (4) described on standard initial Core Description (lCD) sheets, (5) examined microscopically using smear slides, (6) sampled for grain size and mineralogical analysis and (7) analyzed for grain-size of fine sands, silts and clays. The longest cores, collected within 0.5 km of the NPS Headquarters in St. Croix Falls, are 6.5 meters long.

All cores are comprised of fine-grained highly organic mud layers and coarse quartz rich sandy layers. The fine-grained layers likely represent quiescent sedimentation, and the coarse layers represent either annual or stochastic hydrologic or geomorphic events. Future cesium-137 dating of the cores will provide age constraints on sedimentation rates and on the ages of large deposition events. Grain size analysis of the fine-grained sediment suggests that as the reservoir fills, the delta is progressing further downstream over time. The mineralogy, density and magnetic susceptibility of the event-based layers will be used to correlate cores and compare above morphology and mineralogy of reservoir sediment to sediment at lnterstate Park.


Hornbach, D.J., and M.C. Hove. 2004. Long term population dynamics of unionid mussels in the St. Croix River, Minnesota and Wisconsin, USA. Abstracts of the World Congress of Malacology, Perth, Australia, July 1 1-16, 2004.

The Effect of the St. Croix Falls Hvdrodam on Riverbed Temperature
Alese Colehour, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Daniel J. Hornbach, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Mark C. Hove, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Kelly R. MacGregor, Geology Department, Macalester College, 1600 Grand Avenue, St. Paul MN3

Recent changes in the operation of the St. Croix Falls dam from peaking to run-of-river may have an effect on the thermal environment of endangered mussel populations at lnterstate Park, a site just downstream of the dam. We hypothesize that a change in dam operation to run-of-river has led to an improvement in the thermal habitat for winged mapleleaf by reducing hourly water temperature variability due to holding back constant flow of water. As part of a research collaboration with the National Park Service, riverbed water temperatures were collected at lnterstate and compared to two sites: Wild River (a control site upstream of the dam) and Franconia (-10 km downstream of lnterstate). Data collected at lnterstate were also compared with data from this location collected in 1998 when the dam was operated as a peaking facility. Other factors such as water depth, depth in the substrate, water discharge, and air temperature were also analyzed. ln June 2009, lB Tag temperature sensors were placed at three locations (lnterstate, Franconia, and Wild River). Four sensors were embedded in stakes (at 0, 5, 10, and 20 cm) and hammered into the riverbed at two shallow (< 1 m) and two deep (>1 m in most cases) sites at each location. A total of 48 sensors were programmed to log once per hour from June 6 until July 7 to the nearest 0.0625o C. Discharge data were downloaded from the USGS waterdata.usgs.gov website. After accounting for water and substrate depth, the magnitude of hourly thermal variation is lower at lnterstate than at Franconia or Wild River. This suggests the reservoir is acting as a temperature buffer for downstream mussel populations. A comparison of temperature data from 1998 and 2009 demonstrates that higher water discharges significantly reduces thermal variation despite pre-run-of-river operation; this suggests that water discharge is at least as important in controlling temperature variability as dam operation. Additional data is being collected during summer and fall 2009, and future analysis will look more closely at water discharge and at air and water temperatures over several seasons.

Bed Sediment Size Distribution and Mineralogy in lndianhead Reservoir, St. Croix River
Karen Jackson,Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Kelly MacGregor, Geology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Dan Hornbach, Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN
Mark Hove. Biology Department, Macalester College, 1600 Grand Avenue, St. Paul MN

Dams alter sediment transport dynamics in rivers by acting as a physical barrier to the downstream movement of bed sediment, and by slowing water velocity and allowing suspended material to settle into the reservoir, The St. Croix Falls Dam, installed in 1907, is just upstream of lnterstate Park, which is host to a large population of native mussels, including threatened and endangered species. over the past 20 years Hornbach and others have documented 90% decrease in the juvenile mussel population at this same location, as well as a gradual decrease in the grain size of sediment at the riverbed there. One hypothesis is that the lndianhead Reservoir above the dam may be a significant source of the fine sediment at lnterstate park. Our goal is to quantify grain size distribution, morphology, and mineralogy of reservoir sediments in an effort to understand river hydrology and sediment transport in the reservoir.

Grab samples and HTH cores were collected along a 1O-km stretch of the reservoir between Wild River and the St. Croix Falls dam. A total of 39 samples were collected in summer 2009. Sediment was dried and sieved, and grain diameter distribution and SEM analysis (to determine grain morphology and mineralogy) was conducted. The bed sediment at the top of the reservoir (near Wild River) is Composed of moderately rounded spherical felsic grains indicating long distance transport. ln addition, there is a smaller fraction of poorly rounded, moderately spherical mafic grains indicating limited transport and closer provenance. Within a kilometer of the dam, bed sediments has a high organic content with some fine spherical sand particles. The sediment is morphologically more angular than sediment further upstream, and has a higher mafic component.

The geometric mean of sediment size distribution decreases from coarse sand near Wild River to fine sand near the dam. Grain size distribution is Gaussian along the majority of the reservoir, although just upstream of the dam sediment size distribution becomes bimodal, indicating an external coarse sediment source is likely. Decreasing sediment diameter demonstrates the majority of the reservoir behaves like a river with respect to water velocity and sediment transport, but the deeper portion nearest to the dam mimics both fluvial and lacustrine environments. The transition between unimodal and bimodal sediment distribution occurs near a deepening of the reservoir, which may suggest a delta is prograding toward the dam. Further work comparing the grain site, composition, and grain morphology of lnterstate Park bed sediment and reservoir sediment will improve our understanding of possible sediment transport from the reservoir to mussel beds downstream. Analysis of down-core changes in sediment will allow us to analyze temporal changes reservoir sedimentation.


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