Inferring lake depth using diatom assemblages in the shallow,seasonally variable lakes of the Nebraska Sand Hills (USA): calibration,validation, and application of a 69-lake training set |
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Authors: | Avery L C Shinneman Danuta M Bennett Sherilyn C Fritz Jens Schmieder Daniel R Engstrom Aris Efting John Holz |
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Institution: | (1) Department of Geosciences, University of Nebraska, Lincoln, NE 68588, USA;(2) Saint Croix Watershed Research Station, Science Museum of Minnesota, 16910 152nd St. North, Marine on St. Croix, MN 55047, USA;(3) Marine Sciences Institute, University of California at Santa Barbara, Santa Barbara, CA 93106, USA;(4) School of Natural Resources, University of Nebraska, Lincoln, NE 68588, USA |
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Abstract: | The Nebraska Sand Hills are a distinctive eco-region in the semi-arid Great Plains of the western United States. The water
table underlying the Sand Hills is part of the High Plains/Ogallala aquifer, an important water resource for the central Great
Plains. Lake levels are affected directly by fluctuations in the water table, which is recharged primarily by local precipitation
and responds quickly to climatically induced changes in regional water balance. Instrumental records are available for only
50–100 years, and paleolimnological data provide important insights into the extremes and variability in moisture balance
over longer time scales. A set of 69 lakes from across Nebraska was used to establish a statistical relationship between diatom
community composition and water depth. This relationship was then used to develop a diatom-based inference model for water
depth using weighted averaging regression and calibration techniques. Development of the inference model was complicated by
strong intra-seasonal variability in water depth and the linkages between depth and other limnologic characteristics, including
alkalinity, water clarity and nutrient concentrations. Analysis of historical diatom communities from eight lakes allowed
for the reconstruction of lake-level fluctuations over the past several thousand years. Comparisons of the more recent portion
of these reconstructions with the instrumental Palmer Drought Severity Index (PDSI) showed that sediment records may not faithfully
reflect short-term fluctuations in water level, except where sedimentation rates are very high. However, large and persistent
changes in moisture availability were discernible even in longer, low-resolution records. Thus, diatoms are a useful addition
to the tools available for understanding past drought in the central Great Plains, especially when trajectories of change
are constrained by data from multiple sites or other proxies. |
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