Nutrient Limitation of Algal Standing Crops in Shallow Prairie Lakes

• Published in: Ecology (Durham) 1976-07, Vol.57 (4), p.664-678
• Main Author: Haertel, Lois
• Format: Article
• Language: English
• Subjects: Algae; Chlorophylls; Nitrates; Nitrogen; Phosphates; Phosphorus; Rain; Sediments; Summer; Watersheds
• ISSN: 0012-9658; 1939-9170
• DOI: 10.2307/1936181

Environmental control of algal standing crops in two non-stratified prairie lakes in South Dakota and Minnesota, USA was investigated by season for 3 years. Multiple regression analysis was performed using chlorophyll a concentration and cell counts as dependent variables. In both lakes physical factors (light, temperature, wind stress and rainfall) were more frequently correlated with changes in algal standing crops than were nitrogen and phosphorous. Both lakes indicated occasional positive correlations with nitrogen. The correlations were greater in the deeper lake. Phosphorous was positively correlated during one season in the deeper lake, never in the shallower lake. Multiple regression analyses using concentrations of nitrate, ammonia, and orthophosphate as dependent variables and physical factors, algal abundance and zooplankton abundance as independent variables showed positive correlations between increases in orthophosphate and nitrate and prior rainfall and wind stress. Ammonia showed strongest correlations with wind stress. The correlations between wind stress and nutrient levels are assumed to result from recirculation of nutrients released at the sediment surface by circulation of the water column and by direct stirring of sediments in shallow water by wave action. The more extensive direct stirring of sediments in the shallower lake is assumed to partially account for the much higher levels of nutrients observed. Depth of lake relative to depth of wave action determines to what extent the sediments of a shallow lake are subject to direct stirring.