370 Natural Resources Systems Copyright Goodheart-Willcox Co., Inc. The standing water is also an ideal breeding ground for many types of insects. Bogs are also important as carbon sinks and as a source of peat moss. As peat moss is harvested for fuel and other commercial uses, habitats are destroyed and stored carbon is released into the atmosphere. Fens A fen is a freshwater wetland fed mainly through ground- water and other moving water sources, such as a spring or stream. The nutrient quality of the water is heavily affected by the types of rocks through which it fl ows. Many fens are located in areas where limestone or volcanic rock are prevalent, which increases the pH and leads to basic water. Fens are similar to bogs but are less acidic and have higher nutrient levels due to the nutritive water sources. Rich fens have a pH above 6.9, have higher nutrient levels, and support a greater variety of plant and animal species than bogs or poor fens. Rich fens often have limestone bedrock, which creates a calcareous or calcium-rich environment. Poor fens have lower pH, less nutrients, and cannot support the same degree of wild- life as a rich fen. The grasses, sedges, and rushes in fens serve as ideal breeding grounds for a variety of amphibians, reptiles, insects and many migratory species, such as the monarch butterfl y, Figure 15-16. Fens are carbon sinks and their peat is also harvested and used as a fuel source and for other commercial purposes. Freshwater Marshes Freshwater marshes are wetlands where water covers the ground for extended periods. The water level varies from a few inches to two or three feet. Marshes are typically treeless and support a variety of herbaceous (non-woody) plants. Found at the edges of bodies of surface water and along slow-moving rivers and streams, freshwater marshes slow down and absorb fl oodwaters and feed water back into local waterways during drier seasons. Some marshes sea- sonally dry out completely for an extended period of time. Freshwater marshes may be tidal or nontidal marshes. Freshwater tidal marshes are affected by the ocean tides because they are located between saltwater marshes and land. The zone where the two types of marshes meet often contains brackish water and a variety of both saltwater and freshwater plants. Nontidal marshes are inland wetlands that are not affected by the tides. Wet meadows, vernal pools, and dry or playa lakes are all types of nontidal marshes. • Wet meadows are grasslands with soil that is saturated or waterlogged after extensive precipitation. The duration and frequency of standing water is shorter in wet meadows than in marshes. • Vernal pools are small, shallow depressions in forests or grasslands that are usually wet only in the early spring or during the winter season. Vernal pools may also be referred to as vernal ponds or ephemeral pools. Birds and Dragons/Shutterstock.com Figure 15-16. Monarch butterflies are one of the most recognized butterfly species in the United States and also one of the major pollinators. They annually migrate more than 3000 miles from Mexico to Canada and use locations such as fens to rest.