Invited Luncheon Speaker - April 1, 2008 - Carrie Jennings, Minnesota Geological Survey

Sediment dynamics in agricultural watersheds of the Minnesota basin

Abstract
The Minnesota River is the major sediment source for Lake Pepin, which is infilling at ten times its pre-settlement rate. The soils in the watershed are developed in loamy parent materials of the Des Moines lobe which, when drained, are prime for agriculture. Evidence from fallout-radionuclide tracing of surface sediment suggests that the fine-textured soils in fields, although a modern (and not pre-settlement) contributor to the sediment load, are not the only source of sediment to the streams and do not completely account for the increase in sediment load to Lake Pepin. Understanding the type, location, and magnitude of sediment sources is essential for guiding management decisions about investments in reducing sediment loads.

We are working to locate and quantify all sediment sources by understanding how the river system behaved during the Holocene under varying climate regimes and how it is responding to land-use and hydrologic change over the last 170 years of human modification. A combination of field and modeling methods are being used in several MPCA-funded collaborative projects involving the MGS, the National Center for Earth Surface Dynamics at the University of Minnesota and the St. Croix Watershed Research Station of the Science Museum as well as local watershed groups.

The channel now occupied by the Minnesota River was created suddenly 11,500 years ago when discharge from Lake Agassiz created the River Warren valley. The incision ranged from 45 m at the headwaters to more than 70 meters near Mankato, 300 km downstream. Modern longitudinal profiles of the tributaries show that the major knickpoints that were created at tributary mouths have migrated tens of kilometers upstream, varying somewhat because of local stratigraphy, watershed area, and runoff amounts. The knick zones separate the basin into an upper watershed, receiving sediment primarily from uplands and streambanks and a lower, incised zone, which receives additional sediment from high bluffs and ravines. Stream gages installed above and below knick zones in the Le Sueur show dramatic increases in sediment loading above that expected from increases in drainage area, indicating substantial inputs from bluffs and ravines. We focus on the Le Sueur basin because of its unusually high sediment loads and well-gaged tributaries and use a combination of remote sensing, field, and stream observations to constrain the contributions of different sediment sources.


Biography
Carrie is a glacial geologist with background in glaciology and geomorphology and an interest in process. She is interested in how glaciers respond to a variety of forces, how that affects the final sediment record in Minnesota, and how this helps us predict the behavior of modern ice sheets. She is also interested in how the distribution of glacial sediment in Minnesota affects the distribution and quality of resources including surface and ground water. She has recently applied her knowledge of the distribution of glacial sediment in Minnesota (as well as the history of landscape and river evolution) to better define sources of sediment to the modern river systems of Minnesota, most notably, the Minnesota River and its tributaries.


EDUCATION:
Ph.D. Geology, University of Minnesota, 1996
Directed by H.E. Wright, Jr., The glacial geology of southwestern Minnesota with emphasis on the deposits and dynamics of the Des Moines lobe
M.S. Geology, University of Minnesota, 1989
Directed by R. LeB. Hooke, Glaciological conditions associated with drumlin occurrence
B.A. Geology, Northwestern University, 1984
Field Camp University of Alaska, 1983


RESEARCH INTERESTS:
-Erosion and transport of glacial sediment by Minnesota rivers
e.g. Jennings et al., 2006 and current funded work on the Minnesota, Redwood, S. Fork of the Crow and Le Sueur rivers and Seven Mile Creek
-Mapping-based study of paleo-glacial dynamics
e.g. Patterson, 1997, 1998; Patterson and Boerboom, 1999; Jennings, 2006
-History of glaciation and the Quaternary stratigraphic record in Minnesota and the Upper Midwest
e.g. Patterson and Wright, 1998; Jennings, 2006 in press
-Quaternary dating methods
e.g. Bierman et al., 1999; Balco et al, 2005
-Sedimentary processes of modern ice sheets-basal transport of debris
e.g. Knight et al., 2000


PRIMARY COLLABORATORS:
Dan Engstrom and Shawn Schottler, St. Croix Watershed Research Station; H.E. Wright, Jr., Lesley Perg, Karen Gran, Dylan Blumentritt, University of Minnesota; Paul Bierman, Univ. Vermont; Peter Knight and Richard Waller, Keele Univ., England; Roger Hooke, Univ. of Maine; John Stone and Greg Balco, Univ. Washington; Jim Cotter, Univ. Minn. Morris; Nigel Wattrus, Large Lakes Observatory, U. Minn. Duluth

RECENT EMPLOYMENT HISTORY:
Minnesota Geological Survey, University of Minnesota. Senior Scientist, 8/2001 – present; 2/96-8/00; Scientist, 6/91-2/96; Associate Scientist, 5/89-6/91. Duties included mapping and research in glacial deposits, landforms and subglacial processes; conveying geologic information to the public, professionals in geology and related disciplines, and policy makers.
Macalester College, St. Paul, Minnesota. Visiting Assistant Professor, 9/00-8/01. Courses taught: Geomorphology (7 students) with field labs; Ice Houses, Green Houses and the Origin of Humans (11 students); January interim, field course on San Salvador Island, Bahamas (20 students, 3 faculty); next term, Glacial and Quaternary Geology; Natural Hazards and Environmental Geology
Department of Geology and Geophysics, University of Minnesota. Associate Graduate Faculty, 5/97-currently; Adjunct Instructor, 9/96-5/97; Instructor, 9/94-95. Courses taught: Glacial Geology (20-45 students); Geology of Minnesota, (70-80 students). Other duties: Grad. Student advisor; external member on Ph.D. committees in Soil Science, Archeology, and Geological Engineering. Search Committee, 2000, Surficial Processes position.
Carleton College, Northfield Minnesota. Instructor, part-time leave replacement two times, 3/97-6/97 and 1/99-3/99. Courses taught: Intro. Geology (Physical) with lab and field trips (28 students); Glacial Geology with lab and field trips (15 students).

PUBLICATIONS (last 5 years):
Journal Articles
2006, Hooke, R. LeB. and C. E. Jennings, On the formation of Tunnel Valleys, Quaternary Science Reviews, in press
2006, Jennings, C.E. Terrestrial ice streams—a view from the lobe. Geomorphology, v. 75 (1-2), 100 – 124.
2005, Balco, G., J.O.H. Stone and C.E. Jennings. Dating Plio-Pleistocene glacial sediments using the cosmic-ray-produced radionuclides 10Be and 26Al American Journal of Science v. 305, p. 1 – 41.
2002, Knight, P.G. R. I. Waller, C. J. Patterson, A. P. Jones, Z. P. Robinson Discharge of debris from ice at the margin of the Greenland ice sheet. Journal of Glaciology, 48 (161) 192-198.

Edited Volumes and MGS Reports of Investigations
2006, Jennings, C.E. Middle Pleistocene Glaciations in North America, P. Gibbard and J. Ehlers, eds., Encyclopedia of Quaternary Science, History of Quaternary Glaciations, in review, Elsevier.
2004, Patterson, Carrie Jennings and Mark D. Johnson. The status of glacial mapping in Minnesota. In, J. Rose, series ed., Developments in Quaternary Science 2, Part II, North America, J. Ehlers and P.L. Gibbard, eds, Quaternary Glaciations - Extent and Chronology, Elsevier, Amsterdam.
2002, Patterson, C.J. and Knaeble, A.R. History of Glaciation in Pine County, Minnesota. In, Boerboom, T.J. project manager, Contributions to the Geology of Pine County, Minnesota: Minnesota Geological Survey Report of Investigations 60, p. 21 – 41.

Maps
2005, Jennings, C.E., and W.K. Reynolds, Surficial geology of the Mesabi Iron Range, Minnesota. Minnesota Geological Survey Miscellaneous Map Series, M-164, scale 1_100,000.
2005, Meyer, G.N., M.A. Jirsa and C.E. Jennings, Aggregate resource potential of Itasca County, Minnesota, Minnesota Geological Survey Miscellaneous Map Series M-131, 6 pls., scale 1:100,000.
2002, Meyer. G. N., and Patterson, C. J., Surficial geology of western Itasca County, Minnesota. Minnesota Geological Survey
2002, Lusardi, B.A., Hobbs, H.C., and Patterson, C.J., Surficial geology of the Faribault 30 x 60 minute quadrangle, south-central Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-130, scale 1:100,000.

Carrie E. Jennings
Minnesota Geological Survey
2642 University Ave.
St. Paul, MN 55114-1057
612-627-4780