Early Limnology of Dworshak Reservoir. Part 1. Limnology. Part 2. Impact of Log Leachates on Phytoplankton. Part 3. Fate of Phytoplankton and Zooplankton Dynamics. Part 4. Bacteriology.

Abstract : The limnology of Dworshak Reservoir, a very deep, cold water reservoir on the North Fork of the Clearwater River in North Idaho was studied in the first three years after filling. The submergence of soils and vegetation in conjunction with an Anabaena bloom in July, 1972, resulted in high bacterial counts increased algal nutrient concentrations over inflow concentrations, the initiation of zooplankton cycling, and anaerobic conditions below 550 feet until late 1973. Deep 02 concentrations have increased since mid 1973. Total dissolved solids as indicated by conductivity, have shown no overall decline from 1972 to 1974 (28 to 19 micromhos). Mean nitrate and orthophosphate concentrations have remained at approximately .05 and .018 mg/1-l respectively, but intense short term fluctuations of nitrate and orthophosphate have periodically taken these nutrients to detection limits. Average phytoplankton cell numbers have sharply dropped at all stations from 3 x 10 6 cells/1-l in 1972 to approximately 400,000 cells/l in 1974. High turbidity in 1974 from shoreline wave erosion and slumping reduced 1974 algal production to levels below projections based upon available nutrients. Carbon-14 uptake showed similar patterns. Declining reservoir productivity is illustrated by overall reservoir means of total zooplankton numbers: 27,300 10/cum in 1972, 18,500 in 1973, and 10,800 in 1974. After 3 years, Dworshak Reservoir dropped from a moderately productive to an oligotrophic body of water.