Lake Water and Sediment

Abstract

In defining the ability of a lake to produce a crop, one begins by taking a unit area for measurement, which is tantamount to saying that productivity is proportional to area. The productivity per unit area, P, has been stated by Hayes to be inversely related to depth, being where m is the mean depth in meters. P will have to be multiplied by a factor K which defines the crop, whether fish, plankton, etc. It is further necessary to recognize that lakes, like farms, are sometimes on good land, sometimes on poor. This important variant may be given numerical expression as a quality index, QI, which is supposed to tell what a given lake could produce if it were considered as of standard depth 5 m. QI was previously determined for a number of lakes on the basis of fish population, factored for length of food chain. It is made to fluctuate around unity so that K is given a value of unity for fish. Finally there is a reducing correction b to be applied to certain measurements on bog lakes, which have, for example, high oxygen consumption and bacterial counts but support few fish. The bog factor may be a function of color. The foregoing considerations lead to the equation urn:x-wiley:00243590:media:lno1959430291:lno1959430291-math-0002 If a measurement were made on fish in a lake of 5 m depth, P would be the same as QI, all other terms having become unity.Measurements are given of the oxygen consumption of water over mud in undisturbed profundal Jenkin cores from 16 east coast Canadian lakes. These are compared with artificial cores made by plunging a Jenkin tube into the mud of a dredge sample, and also with surface mud packed by centrifuge in bottles. All three methods gave the same values. On four lakes the field hypolimnetic deficit was compared with the laboratory tests. The mean oxygen consumptions were indistinguishable, but the field results did not arrange the lakes in the same order as laboratory tests and are judged to be related to basin dimensions rather than to productivity. Laboratory tests appear to be more accurate than field tests and of wider applicability, e.g., to unstratified lakes or bog lakes. In laboratory tests a water blank is subtracted so that consumption can be obtained for mud surface only.For 9 lakes a regression is calculated between oxygen consumption and QI for fish. The relation is highly significant and is given as urn:x-wiley:00243590:media:lno1959430291:lno1959430291-math-0003 where the units of oxygen consumption are mg used per cm2 mud surface per day.