Some Limnological Features of a Shallow Saline Meromictic Lake

Seasonal variations of some physical, chemical, and biological features were studied from I~cccmbcr 1954 to October 1956 in Hot Lake, a shallow saline body of water occupying a former epsom salt excavation in north central Washington. The lake is meromictic and (luring the period of study had an average salt gradient of approximately 100 g/liter at the surface to 400 g/liter at the bottom, the major salt being magnesium sulfate. The mixolimnion was thin enough that the monimolimnion was heated directly by the sun, with the result that temperatures in cxccss of 50°C were recorded in t,hc monimolimnion during summer. Much of this heat was retained during the winter. The calculated value of heat gain in tho monimolimnion agreed reasonably well with the observed value. The flora consisted mainly of Chara, a bottom mat of blue-green algae, and a dense population of green sulfur bacteria in the upper part of the monimolimnion. Artemia salina was the dominant zoonlankter. and some features of its life history as afTected by the unusual thermal propertic; of the l&e are dcscribcd. The purpose of this paper is to report some physical, chemical, and biological features of an unusual meromictic saline lake located near Oroville in north central Washington. The region is semi-arid and has a moisture index value of 20 (Thornthwaitc 1948). The paper is a contribution from a project directed by Dr. W. ‘1‘. Kdmondson, on Limnology of Arid Lands, currently being carried out at this institution under the sponsorship of the State of Washington Research Fund in Biology and Medicine and the National Science Foundation. Although the major portion of the project has been conccrncd with lakes in a somewhat more arid region, the Columbia Hasin, the present lake was included in the illvcstigation because of its unusual qualities. morphic rocks, dolomitcs, and shales, and in the drainage area surrounding the lake arc numerous mineral deposits consisting mostly of pyrite and pyrrhotite bodies which were largely oxidized to a mixture of iron oxides, quartz, clay, and gypsum. Whitish drainage streaks led from the dcposits to the lake, and from this evidence *Jenkins postulated the following: There have been two separate invcstigations of IIot Lake in the past. St. John and Courtney (1924) investigated the flora of the lake and drainage region but confined their studies to the vascular plants. Only one species of vascular plant inhabited the I:~k.e, Distichlis spicata (L.) Greene. “These facts suggest the possibility that the sulphates and sulphuric acid, known to form from the oxidation of pyrite and pyrrhot)ite through the action of meteoric water and air, acted upon the dolomite and other magnesian rocks, forming magnesium sulphate, which is soluble, and calcium sulphate, which is much less soluble. The result was that the magnesium sulphate was carried to the lake in solution. What littlc calcium sulphatc came with it was precipitated first, being less soluble, as a thin layer of gypsum over the sediment already deposited on the bottorn of the lake. ” Jenkins (1918) described the geology of the region and advanced an explanation for the origin of salts in the Iako. The lake bed lies close to rock consisting of metaThe dominant mineral, epsomite (MgS04.7&0), was in great enough quantity that during and for a short time after the first World War, cpsom salt mining operations took place in the lake. These operations revealed a solid E-foot layer of epsomite bcncath the l&c bottom. Between the layer of cpsomitc and bed