A comparative analysis of the relationship between phytoplankton standing crops and environmental parameters in four eutrophic prairie reservoirs

Abstract

An analysis was performed with multivariate statistical methods of the relationship between chlorophyll a concentrations and eighteen physico-chemical parameters measured over a six year period in four eutrophic Nebraska reservoirs . In the reservoirs with relatively clear water early in the growing season, physical factors (Secchi depth, turbidity, temperature) and non-nutrient chemical factors (alkalinity, hardness, C .O. D .) were significantly related to chlorophyll a concentrations, but macronutrients (nitrogen and phosphorus) were not . In the reservoir with persistent abiogenic turbidity, chemical factors including nitrogen and phosphorus were significant but physical factors were not . Six models based upon intercorrelations between measured parameters and chlorophyll a are evaluated for their usefulness in accounting for chlorophyll a variance. The best model accounts for 67 -70 percent of the total variation in chlorophyll a in the four reservoirs .

Eutrophication of the salt valley reservoirs, 1968–1973 II. Changes in physical and chemical parameters of eutrophication

“…As was indicated previously, turbidity in Wagon Train is caused mostly by colloidal silt and clay particles while in the other reservoirs it is caused by phytoplankton . Schwartzkopf & Hergenrader (1978) observed a highly significant (p < .o1) positive relationship between turbidity and chlorophyll a in Stagecoach, Pawnee, and Branched Oak reservoirs, and a significant (p < .o5) negative relationship between the same two parameters in Wagon Train . In 1969 turbidity was extremely high in Wagon Train (x 111 mg/1), a result of the large inflow of runoff which occurred in that year .…”

“…These episodes, being dependent upon mixing, if repeated at frequent in- tervals, would be a mechanism for periodic injections of phosphorus from the sediments to the water . If such a mechanism exists in the study reservoirs, it could explain why their phytoplankton crops are not correlated with the phosphorus concentrations present (Schwartzkopf & Hergenrader, 1978) .…”

“…2) . In the three clear reservoirs Secchi disk transparency is directly related to the abundance of planktonic algae while in Wagon Train inorganic turbidity controls Secchi disk visibility (Schwartzkopf & Hergenrader, 1978) . A regression of mean Secchi disk transparency on reservoir age (data from Wagon Train excluded) yields a correlation coefficient that is highly significant (R = -.838 ; p < .oi ) .…”

“…First, although all fractions have declined, the reservoirs are not phosphorus-limited but rather have sufficient concentrations to place them in the hypereutrophic category . Schwartzkopf & Hergenrader (1978) examined the relationships between phytoplankton standing crops and various parameters, including phosphorus, in the study reservoirs . Neither total filtrate phosphate nor orthophosphate was significantly related to standing crops in Pawnee, Branched Oak, or Stagecoach reservoirs .…”

Eutrophication of the salt valley reservoirs, 1968–73 I. The effects of eutrophication on standing crop and composition of phytoplankton

“…Wind mixing produces a reasonably homogenous distribution of both heat and N TRAIN nutrients and provides suitable conditions for vigorous algal growth. Nutrient concentrations present are well above those suggested by Vollenweider (968) as necessary for phytoplankton to grow to bloom proportions (Schwartzkopf & Hergenrader, 1978).…”