LIMNOGEOLOGY OF URBAN AND SUBURBAN LAKES IN INTERDISCIPLINARY GEOSCIENCE EDUCATION

Workshop classes or lab sections using short cores from urban and suburban lakes encourage students to consider the development of their surroundings and the interface between nature and culture. The historical and social dimensions of pollution, land use change, and management decisions are more compelling to many students than is climate change on the scale of thousands of years; “neopaleolimnology,” then, can act as a gateway to motivate the study of deeper time. Working on a relatively short record also makes the number of samples tractable. Limnogeology draws on many other geoscience courses (e.g., sed/strat, glacial, geochron, geochem, mineralogy, geomicrobiology), as well as other branches of science and the liberal arts disciplines mentioned above. Students with different academic backgrounds can thus contribute to class discussions as interdisciplinary collaborators.

Asking the students to form specific hypotheses prior to class field work makes them think about sedimentary processes. Students readily predict differences in grain size and plant communities from shoreline to deep water; less intuitive but possible to derive from known concepts are redox-related depositional features, authigenic and diagenetic mineral precipitation, and identification of turbidites, debris flows or slumps, and unconformities. A transect of three or four cores from shallow to deep water can be used to teach about sedimentary facies, correlation, and transgressive/regressive sequences. Historical research can be conducted online and through local societies, and airphotos provide information about land-use changes since the 1920s or ‘30s. Relatively simple or visual analytical methods are best, including lithological core description, LOI, SEM, XRD, and grain size. Isotopes may be frustrating. Smear slides viewed with a petrographic scope (and using the new TMI online reference available from LacCore) are perhaps limnogeology’s simplest and yet most powerful technique. Some age control is critical: if radiometric or biostratigraphic dating (or correlation with previously dated cores) is not available, students might be asked to try to identify a given time horizon based upon lithological changes. Presentation to the department of a single class poster gives students experience and satisfaction.