Comparative Primary Productivity of Two Flood Control Reservoirs in the Salt Valley Watershed of Eastern Nebraska

Primary productivity, Secchi disc visibility, chlorophyll, and nutrient concentrations were studied in Wagon Train and Stagecoach reservoirs during the years 1969 and 1970. The reservoirs are separated by a distance of only 12 km and are similar in nutrient content and circulation pattern. Furthermore, in both reservoirs 92-100% of the productivity occurs in the upper two meiers. However, the reservoirs differ markedly in their underwater light conditions and, consequently in their primary productivity; Wagon Train Reservoir is turbid due to suspended silt and clay particles while Stagecoach Reservoir lacks this turbidity. During the summer months blue-green algal blooms occur frequently in Stagecoach Reservoir but only rarely in Wagon Train Reservoir. This appears to be due to the rapid attenuation of light by the suspended silt and clay particles. In Wagon Train Reservoir, increased primary productivity is usually associated with increased Secchi disc visibility, while in Stagecoach Reservoir, increased primary productivity is often associated with decreased Secchi depths. Inorganic turbidity is an important factor affecting the productivity of Wagon Train Reservoir while algal production itself determines turbidity in Stagecoach Reservoir. Annual productivity in both study reservoirs, when compared to published values for carbon uptake from other lakes and reservoirs, rates very high. Stagecoach Reservoir fixed 530 g Cjm 2jyear in 1969 and 834 g Cjm 2jyear in 1970. Wagon Train Reservoir increased from 148 g Cjm2jyear in 1969, a year of high inorganic turbidity, to 453 g Cjm 2jyear in 1970, a year of reduced inorganic turbidity.