Small lakes (<10Ac) with alkalinity of > 50 ppm and high pH.
The pH of hard bog lakes is at or slightly above neutral, due to groundwater influence. This mineral-rich environment commonly supports a genus of macroalgae called muskgrass (Chara spp.), which in turn supports diverse aquatic invertebrates. As the muskgrasses extract carbon dioxide from calcium bicarbonate, they produce calcium carbonate that precipitates on the lake bottom in the form of marl. Many muskgrass populations have a hard or crunchy texture due to the crusty layer of marl that often precipitates on the plant's surface. If nutrient levels get very high, eutrophication may occur, resulting in a muddy false bottom as the remains of poorly decomposed microscopic plants and animals accumulate. A quaking sedge mat (often Carex lasiocarpa) typically occupies the margins of the lake, providing a substrate for pioneering Sphagnum. If conditions allow (e.g., low lake levels during dry years), this sedge mat may advance into the lake and eventually transition to poor fen. Indicators of groundwater influence are present in the vegetation surrounding the lake, even during later successional stages of the bog mat. These include distinctive species such as white beak-rush (Rhynchospora alba), bogbean (Menyanthes trifoliata), pink-flowered orchids ((grass pink (Calopogon tuberosus), rose pogonia (Pogonia ophioglossoides)), dragon's-mouth (Arethusa bulbosa), and tamarack (Larix laricina). Associated fish species include central mudminnow, yellow perch, golden shiner, fathead minnow, northern redbelly dace, finescale dace, and brook stickleback.
