A Long-Term Database for Plankton Populations and Nutrient Levels in Prairie Lakes

A database for prairie lake phytoplankton populations, zooplankton populations, physical variables and chemical variables is presented. Samples are taken from two time periods, 1970-1979 and 1988-1997. Six lakes, Pickerel, Enemy Swim, Cochrane, Hendricks, Oak and Bitter were sampled during both time periods. Bluedog lake was sampled only in the earlier time period and Roy, East Oakwood, Tetonkaha, Round, and South Buffalo lakes were only sampled in the later time period. Water transparency and population numbers of copepods and cladocerans declined in five of the six lakes sampled in both time periods. Chlorophyll a concentrations and Trophic State Index increased in those five lakes, even though total nitrogen concentrations did not change and total phosphorus concentrations actually decreased slightly in three of the five lakes. The lack of increase in nutrients suggests that the decrease in water transparency and increase in trophic state is cause by biological factors, particularly the decline in numbers of the larger cladocerans and copepods which filter the water and increase transparency. The sixth lake, Bitter, experienced greatly increased water transparency, increased numbers of cladocerans and copepods, decreased Chlorophyll a concentrations, and decreased trophic state after a dramatic rise in water levels that more than doubled the volume of the lake in the mid 1990’s. As the decrease in water transparency, and increase in Chlorophyll a may result in increased shallowness and decreased future recreational value of the lakes, investigation into reasons for the changes should be of highest priority