THE TROPHIC-DYNAMICS OF AN ALKALINE-SALINE NEBRASKA SANDHILLS LAKE

A study was undertaken to determine the tropho-dynamics of a highly alkaline-saline lake ecosystem in the Nebraska sandhills. Sampling was carried out from June 1977 to August 1980, in Border Lake, Garden County, Nebraska. Zooplankton was sampled utilizing a Clarke-Bumpus sampler. Primary productivity was estimated using dark-light C-14 technique. Benthic consumer production was estimated by taking quantitative core samples. Caloric values and assimilation efficiencies were also determined and used to produce energy flow diagrams. Border Lake consumer populations consist of Artemia salina (brine shrimp), the rotifers, Hexarthra jenkinae and Brachionus sp., and Ephydra hians (brine flies). In 1979 and 1980 the cladoceran Moina hutchinsonii was also presented. Alkalinity ranged from 4978 ppm to 66461 ppm during the study period. Associated with the changes in alkalinity was a change in the consumer populations from an Artemia dominated system at high alkalinity to an Ephydra-rotifer dominated system at low alkalinity. At the lower alkalinity Moina hutchinsonii became a significant consumer population. Primary productivity was dominated by benthic algae. Daily productivity of benthos was found to be as high as 33.8 g C m(\u27-2)day(\u27-1) making Border Lake one of the most productive systems recorded. Ephydra were the dominant consumers in Border Lake except in 1977, when Artemia had the highest production. High lake consumer production was found to be the result of the high primary production and high bacterial production, rather than high efficiencies. Consumer growth efficiences were similar to those found for other aquatic systems, although Epydra showed relatively low growth efficiency. These alkaline-saline lakes appear to be important water fowl feeding areas. It is in this capacity that these systems are the most valuable to man