Some Observations on Internal Recycling, Regeneration and Oscillation of Dissolved Nitrogen and Phosphorus in Shallow Self-contained Lakes
Archiv für Hydrobiologie Volume 73 Number 3 (1974), p. 334 - 360
published: Jun 4, 1974
ArtNo. ESP141007303004, Price: 29.00 €
From the fluctuations in mass of nutrients in the water column of four productive shallow lakes in the Erickson area, southwest Manitoba, it is possible to assume that the decomposing plankton is an important source of ammonia and phosphate. The cycle of these nutrients appears to be essentially internal and periodically repeated. The nutrients were released from decomposing algae during totally or partially anoxic conditions in mid-winter under the ice and during short periods in the summer following the collapses of algal blooms. The ammonia and phosphate was subsequently assimilated by algae, transformed into particulate or dissolved organic form and released again. Oscillatory pattern of rates of chemical changes in the bloom-collapse period was demonstrated. Dissolved organic nitrogen and dissolved organic phosphorus were produced by both living and decomposing algae. The midwestern pothole winterkill lakes are small water bodies located in isolated depressions. They lack any permanent inflow or outflow, and depend on temporary surface runoff and groundwater seepage for their water supply (Fig. 1). The lakes are usually shallow (2-3 m) with no pronounced thermal stratification. Some of the surrounding land is intensively farmed and the lakes have reached high degrees of eutrophy. Many of the lakes experience noxious algal blooms in the summer. In addition most of them also develop anoxic conditions during the 5-6 month long ice cover period. Hence the name "winterkill" lakes. In spite of this drawback, these lakes represent a great potential for summer fish farming (JOHNSON et al. 1970). In this paper some observations on internal recycling of dissolved nitrogen and phosphorus are presented. They deal with four representative shallow self-contained lakes, with the objective of determining the mechanism and kinetics of chemical changes taking place during characteristic periods of the annual cycles of the lakes. This work presents a part of broader chemical-limnological studies, currently in progress as a part of the aquaculture program of the Freshwater Institute.