Twentieth‐century salinity and water‐level fluctuations in Devils Lake, North Dakota: Test of a diatom‐based transfer function

Diatom surface-sediment assemblages and associated water-chemistry data are used to develop a transfer function for the quantitative reconstruction of salinity change in the northern Great Plains of North America. The transfer function, derived from canonical correspondence analysis (CCA) of the surface-sample data, is applied to a core from Devils Lake in sediments encompassing the last century. The accuracy of the calibration equation is tested by comparing the diatom-inferred salinity with documented salinity and water-level data recorded for the lake over the last 100 yr. The diatombased reconstruction shows good agreement with the historical data, particularly in freshwater and at low to moderate salinities. Discrepancies between the measured and diatom-inferred salinity during high-salinity periods may reflect inadequacies with the inference method itself or more likely problems in the sedimentary record of the lake related to poor diatom preservation, sediment mixing and reworking, and dating inaccuracies. This diatom-based inference method for salinity reconstruction represents a powerful tool for paleohydrologic and paleoclimatic reconstruction in semiarid and arid regions. The hydrologic budgets of lakes are tied intricately to climate, and significant fluctuations in lake levels are often correlated with periods of climatic change. These linkages are clearly visible in the rising water Acknowledgments Most of the North and South Dakota diatom surface samples were counted by R. W. Battarbee, who played a major role in the development of the ideas presented here. D. R. Engstrom is also a primary collaborator in this saline-lake research and provided the 2’0Pb and water-chemistry data. G. Battarbee, S. Bjorck, D. R. Engstrom, S. Patrick, and G. 0. Seltzer assisted with fieldwork and S. J. Juggins and A. C. Stevenson with statistical analysis of the data. The manuscript benefited from a critical review by P. R. Sweets. This research was funded by NSF grants DEB 8004286 and BSR 84-l 5866, This is Limnological Research Center Contribution 401. levels in the north-central United States over the last decade, associated with increased precipitation (Quinn 198 1). The reconstruction of past fluctuations in lake levels can provide a framework for understanding modern hydrologic conditions and a tool for predicting future hydrologic responses to climatic change. These data can also provide analogues of precipitation patterns during past warm periods, as well as a means of validating general circulation models that are used to simulate global climatic change. Closed-basin lakes in regions with a negative water balance are powerful paleohydrologic and paleoclimatic recorders (StreetPerrott and Roberts 1983). In such systems fluctuations in the balance between precipitation and evaporation result in both changes in lake level and the concentration or dilution of dissolved salts. In turn the fluctuations in salinity are recorded in a variety of paleolimnological indicators, including the community composition of diatoms (Bradbury et al. 1989; Gasse et al. 1987) and ostracods (De Deckker and Forester 1988) the trace-metal composition of ostracod shells (Chivas et al. 1986) the geochemistry of chemical precipitates (Last and Schweyen 1983), and the partitioning of isotopes in nondetrital carbonates (Gasse et al. 1987). In contrast, freshwater lakes in regions with a positive water balance are unlikely to contain as clear an archive of past climate, because water chemistry in these basins does not change sufficiently to leave a paleosalinity record, and because other kinds of limnological changes are confounded by many nonclimatic factors. The sedimentary record of saline lakes can therefore be used to reconstruct past fluctuations in salinity, and, given regional pat-