Eutrophication Trends of Bear Lake, Idaho-Utah and Their Effect on the Distribution and Biological Productivity of Zooplankton

Zooplankton of the littoral and limnetic zones of Bear Lake, Idaho- Utah, were collected over a 17 -month period. Twenty-three species of zooplankton were recorded, as well as nine other species represented by both flora and fauna. At the time of sampling 17 physical and chemical parameters were also measured. Methods of analysis for the plankton and the environment are described and discussed. The objectives of this project were fourfold: To establish a record of the current zooplankton population before changes due to the increase o f organic nutrients occur. To compile a qualitative and quantitative standard against which future populations can be compared. To assess the source and the amount of present nutrients which are being contributed to the lake. To investigate the effect the present addition of nutrients is having on zooplankton productivity. The physical and chemical analysis of the Bear Lake waters showed a number of interesting trends. The measurement of total dissolved solids, when compared with previous investigations, showed a decline: i.e., it appears that a great dilution had taken place in the lake waters since 1912. The measurement of salinity revealed two chemical patterns in Bear Lake waters. First: chloride, sulfate, sodium, and potassium showed a decrease in concentration on a long-term basis. Second, calcium showed a slight rise with a leveling off, and magnesium showed a decline with a leveling off over the same period. Calcium is being precipitated as calcium carbonate, and the removal of sodium, potassium , sulfate, magnesium, and chloride is achieved through the pumping of lake waters outside the basin. Nitrogen was measured with respect to three of its forms--ammonia, nitrite, and nitrate. Ammonia was comparatively evenly distributed throughout the water column at all depths. The cycling of ammonia appeared to follow that of known oligotrophic lakes. Generally, the nitrite was low in the limnetic and allochthonous waters and higher in the littoral zone. The littoral and limnetic water exhibited lower nitrate levels than the allochthonous sources. This is believed to be due to the prevailing land use patterns. The production of cattle and sheep and the cultivation of extensively fertilized crops appear to give the most plausible answer. The littoral waters appeared to be higher with respect to ammonia, nitrite, and nitrate, in the microhabitats that are natural, and in others that are man-made: i.e., harbors, breakwaters, and shore based homes. The distribution of phosphate-phosphorous in the waters varied little during the study. The mean values were quite similar for the littoral and limnetic waters. The allochthonous waters had approximately four times the phosphate concentration of the lake waters. The chemical analysis of the bottom muds revealed that phosphorous as phosphate and as P2O5 were significantly higher in concentration between the 50- and 200-foot contours than at lesser depths. The low levels of soluble phosphate and the slight variation encountered in the water column seem to be related to the orthograde nature of the oxygen curve found in the lake. Relationships between chemical analysis and the zooplankton associated within a particular station in the lake were completed by correlation and regression analysis. Associations between independent and dependent variables apparently defined various environmental preferences or requirements necessary for the maintenance of particular individual species. In light of the basic taxonomic considerations these proposals appear to be within reason. Individual correlation and regression analysis were completed for three lake zones investigated: littoral, limnetic, and the haptobenthos. Individual analysis of variances were completed within the three Bear Lake zones in order to assess the affect of habitat on the plankton population. The statistical analyses were compared to the means for these several stations within one zone, and biological and statistical explanations were made. Supplementary water quality analyses were conducted in order to explain some abnormal chem1cal and biological results. Bacteriological testing of the Bear Lake waters revealed that a large percentage of the littoral and allied limnetic zone presented definite problems with respect to water quality and public use