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Part of the Earth Sciences CommonsThis Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska -Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska -Lincoln.Shinneman, Avery L. C.; Bennett, Danuta M.; Fritz, Sherilyn C.; Schmieder, Jens; Engstrom, Daniel R.; Efting, Aris; and Holz, John, "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" (2010 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 diatombased 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.

Bioavailable phosphorus (BAP) plays an important role in phosphorus (P) release from lake and river sediments, as well as serves as an indicator for the potential P-release risk in sediment. Developing a feasible model which could predict BAP via other P fractions is needed for the lakes and reservoirs without regular BAP monitoring. The algal available P (AAP), NaHCO 3 extractable P (Olsen-P), water soluble P (WSP) and readily desorption P (RDP) are four fractions of BAP. The vertical and spatial distributions of BAP fractions of three sediment cores from Jiulongkou Lake were analyzed. In addition, the P fractions, including total P (TP), organic P (OP), inorganic P (IP), non-apatite inorganic P (NAIP), and apatite P (AP) were measured to develop a model for predicting BAP. The model for each BAP fraction was developed based on datasets from Jiulongkou Lake and validated by the datasets collected from Wujin and Wugong Lake. The results showed that all of the four BAP fractions decreased with depth, along the direction of contaminant transport. Their rank order was AAP [ Olsen-P [ WSP [ RDP in all samples. The concentration of BAP was affected by the anthropogenic input and aquatic macrophyte growth. Each of the four BAP fractions could be simulated by different P fractions: both AAP and Olsen-P were expressed by NAIP and OP, WSP had a significant relationship with OP, and RDP had significant relationship with IP. NAIP and OP were the major sources of the BAP fraction. The simulated results in two other lakes further illustrated that this model could be used to successfully predict the BAP concentrations in lakes in the study area, and holds promise for predicting the BAP levels in other lakes and reservoirs as well.