Wetlands are where water is present above or near the surface of soil. The prolonged presence of water creates conditions that favor the growth of specially-adapted plants and promote the development of wetland or hydric (wet) soils. Water saturation determines the types of plant and animal communities living in and on the soil. Wetlands vary depending on soils, topography, climate, water chemistry and vegetation.
Wetlands in Boulder Valley:
- are considered inland waters;
- most common on floodplains along creeks or streams, in isolated depressions surrounded by dry land and along the margins of ponds and reservoirs;
- include riparian areas, marshes, wet meadows, mudflats and alkaline (salt) flats; and
- dry for one or more seasons of every year and wet only periodically.
The quantity of water present, and the timing of its presence, determine the functions of a wetland and its role in the local environment. Even wetlands that appear dry most of the time, such as wet meadows where the water level may be just below the surface of the ground, often provide critical habitat for wildlife adapted to breeding exclusively in these areas. Boulder’s wetlands support several rare or endangered species such as Preble’s meadow jumping mouse, Ute ladies’ tresses orchids and great blue heron.
What are streams, creeks and watersheds?
Streams or creeks are open, relatively natural channels that collect and drain flows within a watershed. A watershed is a geographic area in which water, sediments and dissolved materials drain from higher elevations to a common low-lying outlet or basin, which could be a point on a larger stream, a lake or estuary. A stream may have water flowing through it year-round, or be dry for most of the year. Streams are different than ditches, which are built and maintained to carry irrigation water to croplands. Since there are several ditches running through the city, it is sometimes difficult to tell a ditch from a creek.
Why are streams and wetlands in the city important to protect?
They are among the most productive ecosystems in the region and the world. Wetlands can be thought of as “biological supermarkets” because they provide volumes of food that support a large diversity of animal species. Riparian areas, in fact, comprise less than one percent of the land area of most western states, yet up to 80 percent of all wildlife species in this region of the country are dependent upon riparian areas for at least part of their life cycles. Streams and wetlands in the urban area also have other critical functions including:
- Enhancing water and air quality;
- Replenishing the ground water supply;
- Collecting and retaining flood waters; and
- Enhancing the aesthetic and recreational aspects of our community.
What is a buffer area and why are buffers important?
A buffer area is the riparian and upland areas adjacent to wetlands or streams. The health of urban streams and wetlands is highly dependent upon maintaining an undeveloped, vegetated buffer area to reduce impacts to water quality and support wildlife habitat. Buffers help protect water quality by:
- Slowing down and absorbing runoff (stormwater runoff picks up and carries oil from roads, soil from construction sites, fertilizers and pesticides from lawns, harmful bacteria from pet waste, and heavy metals from buildings);
- Reducing and preventing erosion (if buffer areas are not managed properly, streambank and channel erosion can result);
- Providing shade for the stream and reducing water temperature;
- Using nitrogen and phosphorous, which are major pollutants in streams and wetlands; and
- Breaking down chemicals like pesticides and herbicides, and converting them to less toxic forms.
What are the common impacts to streams and wetlands in Boulder?
Impacts are often a result of the removal of vegetated buffer areas. In a natural setting, ground vegetation and natural debris in adjacent “buffer areas” allow most precipitation to be intercepted and delivered to the stream as groundwater. Groundwater is often the primary source of water for the stream and the trees in the buffer area – especially in the fall and winter, when streamflow is minimal.
When vegetation is removed and replaced with impervious surfaces such as driveways, patios, parking lots or structures, high-flow events in the stream become more frequent, leading to increase flooding, streambank erosion and destabilization. Between storm events, less groundwater feeds the streams, raising water temperature and potentially drying out the stream. In addition, the quality of the stormwater is affected as this increased runoff picks up pollutants such as eroded soil, oil, spilled gasoline, fertilizers, pesticides and pet waste.