Seasonal Variations in Water Chemistry and Primary Productivity in Four Alkaline Lakes in the Sandhills of Western Nebraska

Between the Platte and Niobrara Rivers in western and central Nebraska lie over 25,000 square kilometers of dune sand. The dunes have lost their sculptured shapes and windswept edges, being shrouded beneath a mantle of grass and fine loess soil. Only at the blowouts, where wind has cut away this mantle forming cavities in the sides of hills, is the sand exposed. Dotting this rolling prairie grassland in the depressions between the dunes are small lakes. Over 2000 lakes of widely varied salinities and alkalinities accent the topography of the dunes. Blue Lake, Roundup Lake, Goose Lake, and Bob’s Lake, all located within the Crescent Lake National Refuge, exhibit a great diversity in their chemical and biological characteristics. These four lakes, which spanned the spectrum of one chemical parameter, alkalinity, were studied over several seasons to establish the interrelationships between the chemical parameters of these waters and their biological constituents. Of no little significance is the proximity of these lakes to one another, ensuring the same potential inocula for each system and minimizing the microclimate variability among the lakes. Each lake is distinctly different in morphometry, chemistry, and history; nevertheless, certain trends became evident when the data for various parameters from each lake were compared. The objectives of this research were to: 1) Identify the range of alkalinity within the lakes near the Crescent Lake National Wildlife Refuge, 2) Select lakes for in-depth study which spanned the observed range of alkalinity, 3) Record the seasonal variations in selected physical and chemical parameters as well as the abundance and composition of the phytoplankton, 4) Determine the rates of primary productivity by C-14 uptake, 5) Determine the effect of the varying measured physical and chemical parameters on the abundance and composition of phytoplankton by correlation analysis, 6) Establish a data base of the limnological conditions within these lakes to serve as a reference for future research. Water samples were collected from the four lakes over an 18-month period between June 1977 and September 1978. Weekly or bi-weekly sampling was conducted during the summers while monthly samples were collected during the remaining period. Marked chemical and biological differences were observed among the lakes studied. Common mechanisms were responsible for the observed variations within each lake. Physical features, most notably the seasonal hydrological cycle of evaporation, dilution, solution, and even at times flooding, controlled many of the parameters studied. Wind also played an important role in each of the lakes, contributing to their formation and determining both their stability and productivity. Differences in morphometry, sediment composition, and history have made each of these lakes unique. The variations observed show that the lakes move in the same directions, but distinctly. Advisor: Gary L. Hergenrade