Wetlands are areas that are saturated with surface water or near-surface groundwater for much of the year. They usually have no clearly defined ecological boundaries, but are a gradient between deepwater habitats, such as lakes and rivers, and upland terrestrial ecosystems, such as conifer forests. Wetlands are differentiated from deepwater habitats by the presence of rooted emergent plants, and distinguished from uplands by nearly continuous soil saturation and the presence of water-tolerant (hydrophytic) vegetation communities and characteristically textured and colored wetland (hydric) soils. These wet soils may have rust colored mottling or be very black in appearance. Palustrine wetland with rooted emergent vegetation.
Wetlands in Yosemite occur in valley bottoms throughout the park, and are often hydrologically linked to nearby lakes and rivers through seasonal flooding and groundwater movement. Meadow habitats, distributed at elevations from 3,000 feet to 11,000 feet in the park, are generally wetlands, as are the riparian habitats found on the banks of Yosemite's numerous streams and rivers.
The park contains three major types of wetland: Riverine, Lacustrine, and Palustrine These wetland types are described below and are also discussed on the U.S. Fish and Wildlife's National Wetlands Inventory Web Site . Each of these types of wetlands varies in geographic distribution, duration of saturation, vegetation community, and overall ecosystem function. All three types of wetlands provide rich habitat for plant and animal species, delay and store seasonal floodwaters, minimize downstream erosion, and improve water quality. Riparian habitat (riverine wetland) alongside the Merced River.
Riverine wetlands are found within river and stream channels and are strongly influenced by seasonal runoff patterns. When inundated, riverine wetlands provide habitat for water-tolerant plants such as willows, and aquatic animals such as tadpoles and immature fish.
Lacustrine wetlands generally occur on river floodplains and along lakeshores and are influenced by seasonal variations in groundwater levels. These wetlands are relatively rare in the park, but support an abundance of warm-water loving plant and animal species.
Palustrine wetlands are typically distinguished from riverine and lacustrine systems by the presence of very dense covers of trees, shrubs, or emergent plants. This wetland type includes wet meadows, densely vegetated riparian habitats, and shallow ponds. They provide cover and forage for wildlife traveling between upland and aquatic habitats.
Since the 1970s the United States has made substantial progress toward protecting and restoring wetland habitats. Yosemite National Park complies with a 1990 Presidential Executive Order that mandates 'no net loss' of wetlands on federally-managed lands, and requires federal agencies to map and protect all existing wetlands. Meadow habitat (palustrine wetland) in Yosemite National Park.
In 1996 the National Fish and Wildlife Service delineated and classified Yosemite's wetlands, through analysis of aerial photographs and topographic maps, as a part of the National Wetlands Inventory Web Site (NWI). Although the NWI maps cover the entire park, they have not been rigorously ground-truthed and only delineate wetlands larger than five acres in size.
The park restores to natural conditions wetlands that have been drained or filled in the past. Most recently in Yosemite Valley, the Cook's Meadow restoration project involved filling old drainage ditches that were draining the meadow and removing an old roadbed that was inhibiting water flow. These actions are currently being monitored with vegetation transects and mapping of surface water to determine how successful the project was in restoring the wetland.