What is a Riparian Zone?
The riparian zone is the green ribbon of life alongside a stream. This ribbon is a
mixture of vegetation types, which varies greatly from place to place. Riparian vegetation
along a desert stream may be small and sparse while the vegetation along a mountain
stream may be tall and lush.
The riparian zone is critical to the health of every stream and its surroundings environment. It connects the upland zone (the area of the watershed that does not receive regular flooding by a stream) to the aquatic zone (the area of the stream channel covered by water, controlling the flow of water, sediment, nutrients, and organisms between the two. Without a proper functioning riparian zone, the other zones suffer.
HOW DOES THE VARIETY OF SPECIES DIFFER IN THE RIPARIAN ZONE?
The riparian zone generally has a greater variety of species than the other zones. It is also denser and more structurally complex (plants have a greater variety of shapes and heights). Plants such as sedges and rushes can be found in the riparian zone and are not found in most of the upland areas because they require a lot of water.
HOW DO PLANTS AFFECT STREAMS?
- Riparian vegetation contributes shade, food, and shelter for aquatic organisms. The riparian zone is also home to many animals that move between land and water, such as insects, amphibians, and waterfowl.
- Riparian vegetation and litter reduces erosion and regulates the overland flow of water to the stream (uplands vegetation serves this function, too).
- The riparian zone acts as a natural sponge, soaking up water as it runs off the land, and slowly releasing that water back into the stream.
HUMAN FACTORS THAT INFLUENCE A RIPARIAN ZONE
Road building may cause accelerated erosion, introduce oil and other pollutants to the stream, cut off subsurface water flow to the stream and threaten wildlife.
Farming can increase erosion of stream banks if the riparian zones are cleared for more farmland. Farmland is lost where the erosion occurs and sedimentation increases downstream. Farmers maintain the health of their riparian areas to ensure long-term sustainability of their land.
Grazing or overgrazing of the riparian zone can cause changes in the types of vegetation and the amount of cover and forage, increase erosion, and introduce increased amounts of nutrients and fecal coliform bacteria to the stream through manure. However, if cattle are managed correctly (herded or fenced out after a short time) they can be a part of a healthy riparian zone.
Dams reduce downstream flooding. while this serves the people who live downstream in the floodplain, it degrades riparian zones. Natural flood cycles are critical to healthy riparian zones. Floods bring essential supplies of water, nutrients and sediment. They also help to create backwater that serve as critical fish nurseries.
Development of riparian zones for housing or commercial development often causes removal of vegetation and alters the stream banks. These changes can increase the intensity of floods, increase the direct input of pollutants to water, and decrease wildlife.
Logging operations today realize the importance of healthy riparian zones and rarely log them. However, logging roads continue to be built through these zones, creating the same problems that all roads do. When upland vegetation is stripped away, too much water is allowed to flow down into the stream at one time, which can lead to bank erosion, deep and narrow channels, shrunken riparian zones, and often increased loads of sediments.
NATURAL FACTORS THAT INFLUENCE A RIPARIAN ZONE
Water Supply is the major factor that regulates the growth of riparian vegetation. Flood waters transport nutrients, sediment, and new seeds from upstream. Floods also strip away larger, established vegetation and allow new seedlings to establish.
Soil type in the riparian zone influences the amount of water and nutrients available. Organic-rich soil holds water and provides abundant nutrients to plants, without releasing these nutrients to the water. We can expect to find denser vegetation in these soils than in a gravely soil with little water-holding capacity and few nutrients.
Topography, or the shape of the land, affects the location and abundance of plants in the riparian zone.
Climate affects the appearances of riparian zones. In the deserts riparian zones are "green oases" in sparse, dry surroundings. Where precipitation is more abundant, like in the mountains, the upland vegetation remains relatively lush.