1: Carbon and Oxygen Isotope Trends in Freshwater Mussels from the Cannon River, MN
Kelly Hereid, Micah Johnson, Dan Jones, Rebekah Lundquist and Bereket Haileab,
Carleton College,One North College Street, Northfield, MN 55057
Abstract
As they precipitate calcium carbonate to make their shells, bivalves record geochemical information on surrounding environmental conditions. Carbon and
oxygen isotopic signatures in freshwater mussel shells result from surrounding water
chemistry and temperature. This study sampled carbon and oxygen isotope data, using
a mass spectrometer, from growth banding throughout the life of one Lampsilis shell
and one Pink Heelsplitter. Significant differences in d 18O between the light and dark
bands in the Lampsilis shell revealed that a light-dark band pair is precipitated annually.
A heavier d18O signature from the light band is due to cool water temperature and possibly
a different source of precipitation to the river during cooler months. Variation
is observed in d 18O and d 13C as the mussel aged, however, data on river conditions during
mussel growth was unavailable, so no climate correlations could be attempted. However, Lampsilis has potential to be a good source of paleoclimate information, and
bivalve shells may prove to be sources of information for high resolution paleoclimate reconstructions.
2: Variation in Trace Element Geochemistry of Freshwater Mussels Lampsilis, Lasmigona complanata, and Potamilns alatus from the Cannon River, Faribault, MN
Keith Christianson, Cicely Miltich, Louise Miltich, Selena Pang and Grant
Rozier and Bereket Haileab, Carleton College,One North College Street, Northfield,
MN 55057
Both marine and freshwater molluscs have been the focus of study because of their ability to record, in their shell layers, some signature of the changing
conditions of the environments in which they live. By observing variation in the amount
of certain trace elements incorporated into successive layers of shell growth, workers
have been able to derive important information about temperature variability, changes
in productivity levels in surrounding water and alterations in climatic conditions. This study focuses on variations in the amount of strontium, barium and manganese incorporated into the successively deposited layers of carbonate
that make up
the shells of freshwater molluscs collected from the Cannon River near Faribault,
Southcentral Minnesota. By combining bulk chemical analysis and electron-microprobe data, fluctuations across time that may indicate some systematic connection between
biological changes, environmental conditions (such as seasonality) and the trace element
chemical composition of the shell material can be identified. Although certain variability
is visible in the data, the ability to attribute these patterns to specific environmental
or biological constraints is limited by a variety of technical and sampling limitations.
The results of this study, however, indicate a strong, systematic variability in the trace
element composition of freshwater molluscs (Lampsilis, Lasmigona complanata, and Potamilns alatus).
3: Chemistry of the Cannon River in southern Minnesota
Andy Ault, Pam Moeller, Dan Shapiro, Sarina Yospin and Bereket Haileab, Department of Geology, Carleton College,One North College Street, Northfield, MN 55057
The chemical properties of river water are an important environmental component determining shell chemistry for bivalves living in the river. This study focuses
on river
water chemistry determined from samples collected from a 13 mile section of
the Cannon River in southern Minnesota. Water samples were collected from three sites
in the sample area (Faribault, Dundas, and Northfield) in the spring of 2005, and
analyzed to determine the alkalinity, ion concentrations, and oxygen and hydrogen isotopic
ratios (d 18O and d 2H). This analysis led to general observations and about the extent
and variability of these properties over the river section studied. Isotope analyses
of the river water were also compared to isotope data of meteoric water from the area. Ion and Alkalinity concentrations increased dramatically between Faribault
and Dundas, but remained relatively constant between Dundas and Northfield, indicating
a possible anthropogenic input source between the Faribault and Dundas locations.
Oxygen isotopic composition between the three sample sites was fairly constant
(d 18O ± 0.5 0/00) but was more enriched in d 18O than local rainwater. This may indicate groundwater interaction. Similar d 2H enrichment was seen in adjusted river
water samples when compared to that observed.