Three-dimensional modeling of lacustrine diatom habitat areas: Improving paleolimnological interpretation of planktic : benthic ratios

Three-dimensional modeling of lake morphometry enables the calculation of lake volume, planar surface area, and basin surface area, which are critical components of a conceptual model of how planktic and benthic habitat areas change with changing lake level. We have applied three-dimensional modeling to Foy Lake, Montana, and compared model results of changing ratios of planktic and benthic habitat areas at all possible lake levels to sediment cores recovered from the lake. The model allows us to produce semiquantitative depth reconstructions and greatly improves lake-level reconstruction of this morphometrically complex basin. The conceptual model also was modified to examine the influence of resuspension versus gravity redistribution of diatomaceous material on the sedimentary record. Comparison of the model results with both long and short sedimentary records from Foy Lake, Montana, suggests that planktic : benthic ratios may be a better predictor of mean lake depth than maximum lake depth. The model developed here is simple enough to be easily implemented, has few requirements, can be adapted to suit any lake basin, and can be augmented to examine a variety of different lake processes that affect habitat availability. The hydrologic response of lakes to climate change varies dependent upon the hydrologic, geomorphic, and climatologic setting of a given lake basin (Almendinger 1990). Regional changes in effective moisture (precipitation minus evapotranspiration) can increase or decrease lake level, altering lake chemistry and the lake surface area to volume ratio (Allen and Anderson 1993; Mason et al. 1994; Wolin and Duthie 1999). Evidence of long-term hydroclimatic variation is apparent in sedimentary records, although the interpretation of past climate from sedimentary signals is often complicated by internal and external factors (Fritz 1996; Dearing 1997; Wolin and Duthie 1999). Lake-level variations cause an immediate change in environment for lake organisms, particularly benthic (attached) organisms with a limited capacity to adjust to lake-level variations (Hoagland and Peterson 1990). Fossil diatoms have been used frequently to reconstruct past lake-level change because of the sensitivity of diatoms to lake conditions, their widespread distribution, and the common preservation of diatoms in sedimentary records. Many lake-level reconstructions based on fossil diatoms have used the ratio of planktic (free floating) to benthic frustules in lake sediment. Such reconstructions are most robust when there is supporting evidence for lake-level change, such as sediment stratigraphy,