Elk Lake is near the present forest-prairie border in northwestern Minnesota, and is also located on the boundary between hard-water lakes that are typical of once-glaciated parts of the north-central United States and more saline prairie lakes of western Minnesota and the Dakotas. The sediments of the prairie lakes just west of Elk Lake are unusual in that they commonly contain high-Mg calcite and dolomite in addition to low-Mg calcite, which is the dominant carbonate mineral in most marl lakes. During the mid-Holocene dry period, prairie conditions expanded eastward into the forested regions of Minnesota. Variations in types and abundances of carbonate minerals in the Holocene sediments of Elk Lake recorded this climatic change.
Studies of primary productivity, carbonate saturation, water chemistry, and sediment-trap samples show that low-Mg calcite precipitates during the summer, triggered by algal photosynthesis. The epilimnion of Elk Lake is always oversaturated with calcite, and the degree of oversaturation increases progressively during the summer. The pH of the epilimnion increases from
