A riparian area is the transition from the aquatic area to the upland area. Vegetation is expected to change from species adapted to wetter sites near the channel to species adapted to drier sites in the upland, with a mixture of species occurring in between. In this example, an assessment of riparian function would consider the riparian areas, mixed riparian/upland areas, and aquatic area in the reach. Not all riparian areas have all of these features.[1]
Ariparian zone orriparian area is the interface between land and ariver orstream.[2] In some regions, the termsriparian woodland,riparian forest,riparian buffer zone,riparian corridor, andriparian strip are used to characterize a riparian zone. The wordriparian is derived fromLatinripa, meaning "river bank".[3]
Research shows that riparian zones are instrumental inwater quality improvement for both surface runoff and water flowing into streams through subsurface orgroundwater flow.[12][13] Riparian zones can play a role in lowering nitrate contamination in surface runoff, such as manure and otherfertilizers fromagricultural fields, that would otherwise damageecosystems and human health.[14] Particularly, the attenuation ofnitrate ordenitrification of the nitrates fromfertilizer in this buffer zone is important.[15] The use of wetland riparian zones shows a particularly high rate of removal of nitrate entering a stream and thus has a place in agricultural management.[16] Also in terms of carbon transport from terrestrial ecosystems to aquatic ecosystems, riparian groundwater can play an important role.[17] As such, a distinction can be made between parts of the riparian zone that connect large parts of the landscape to streams, and riparian areas with more local groundwater contributions.[18] Additionally,Richardson et al. showed that warming, nutrient enrichment, and predators interactively affect emergence, decomposition, phenology, and carbon cycling in riparian-stream systems.[19]
- Riparian forests often host plant species that have high moisture requirements.
- The flora typically includes species native to the region, adapted to the moist conditions provided by proximity to water bodies.
In summary, riparian forests are characterized by their location along waterways, their intricate interplay with water and soil dynamics, a diverse array of vegetation layers, and a plant composition favoring moisture-dependent species.
A well-preserved natural riparian strip on a tributary toLake Erie
Riparian zones dissipate stream energy.[20] Themeandering curves of a river, combined with vegetation and root systems, slow the flow of water, which reduces soil erosion and flood damage.[21] Sediment is trapped, reducing suspended solids to create lessturbid water, replenish soils, and build stream banks.[22] Pollutants are filtered from surface runoff, enhancing water quality via biofiltration.[3][23][24]
The riparian zones also providewildlifehabitat, increased biodiversity, andwildlife corridors,[25] enabling aquatic and riparian organisms to move along river systems avoiding isolated communities.[26] Riparian vegetation can also provideforage for wildlife and livestock.[22] Additionally, riparian vegetation supports the reproduction of species such as dragonflies, whose diverse egg-laying strategies depend on the presence of specific plants and substrates along stream banks.[27]
Riparian zones are also important for the fish that live within rivers, such as brook and charr.[28] Impacts on riparian zones can affect fish, and restoration is not always sufficient to recover fish populations.[29][30]
They provide nativelandscape irrigation by extending seasonal or perennial flows of water.[31] Nutrients from terrestrial vegetation (e.g.plant litter and insect drop) are transferred to aquaticfood webs, and are a vital source of energy in aquatic food webs.[32] The vegetation surrounding the stream helps to shade the water, mitigatingwater temperature changes. Thinning of riparian zones has been observed to cause increased maximum temperatures, higher fluctuations in temperature, and elevated temperatures being observed more frequently and for longer periods of time.[33] Extreme changes in water temperature can have lethal effects on fish and other organisms in the area.[32] The vegetation also contributes wood debris to streams, which is important to maintaininggeomorphology.[34]
Riparian zones also act as important buffers against nutrient loss in the wake of natural disasters, such ashurricanes.[35][36] Many of the characteristics of riparian zones that reduce the inputs of nitrogen from agricultural runoff also retain the necessarynitrogen in the ecosystem after hurricanes threaten to dilute and wash away critical nutrients.[37][38]
From a social aspect, riparian zones contribute to nearby property values through amenity and views, and they improve enjoyment for footpaths and bikeways through supportingforeshoreway networks. Space is created for riparian sports such as fishing, swimming, and launching for vessels and paddle craft.[39]
The riparian zone acts as a sacrificial erosion buffer to absorb impacts of factors includingclimate change, increased runoff fromurbanization, and increasedboat wake without damaging structures located behind a setback zone.[40][41]
"Riparian zones play a crucial role in preserving the vitality of streams and rivers, especially when faced with challenges stemming from catchment land use, including agricultural and urban development. These changes in land utilization can exert adverse impacts on the health of streams and rivers and, consequently, contribute to a decline in their reproductive rates."
The protection of riparian zones is often a consideration inlogging operations.[42] The undisturbed soil, soil cover, and vegetation provide shade, plant litter, and woody material and reduce the delivery ofsoil eroded from the harvested area.[43] Factors such as soil types androot structures,climatic conditions, and vegetative cover determine the effectiveness of riparian buffering. Activities associated with logging, such as sediment input, introduction or removal of species, and the input of polluted water all degrade riparian zones.[44]
Riparian zone along Trout Creek in theTrout Creek Mountains, part of the Burns Bureau of Land Management District in southeasternOregon. The creek provides critical habitat fortrout.
The assortment of riparian zone trees varies from those of wetlands and typically consists of plants that are either emergent aquatic plants, orherbs,trees andshrubs that thrive in proximity to water.[45] In South Africa'sfynbos biome, Riparian ecosystem are heavily invaded by alienwoody plants.[46] Riparian plant communities along lowland streams exhibit remarkable species diversity, driven by the unique environmental gradients inherent to these ecosystems.[47]
Riparian forest can be found inBenin, West Africa. In Benin, where the savanna ecosystem prevails, "riparian forests" include various types of woodlands, such assemi-deciduous forests, dry forests, open forests, andwoodland savannas. These woodlands can be found alongside rivers and streams.[48] InNigeria, you can also discover riparian zones within the Ibadan region of Oyo state. Ibadan, one of the oldest towns in Africa, covers a total area of 3,080 square kilometers and is characterized by a network of perennial water streams that create these valuable riparian zones.[48] In the research conducted by Adeoye et al. (2012) on land use changes in Southwestern Nigeria, it was observed that 46.18 square kilometers of the area are occupied by water bodies. Additionally, most streams and rivers in this region are accompanied by riparian forests. Nevertheless, the study also identified a consistent reduction in the extent of these riparian forests over time, primarily attributed to a significant deforestation rate.[49] In Nigeria, according to Momodu et al. (2011), there has been a notable decline of about 50% in the riparian forest coverage within the period of 1978 to 2000. This reduction is primarily attributed to alterations in land use and land cover. Additionally, their research indicates that if current trends continue, the riparian forests may face further depletion, potentially leading to their complete disappearance by the year 2040.[49] Riparian zones can also be found inCape Agulhas region of South Africa.[citation needed] Riparian areas along South African rivers have experienced significant deterioration as a result of human activities. Similar to many other developed and developing areas worldwide, the extensive building of dams in upstream river areas and the extraction of water for irrigation purposes have led to diminished water flows and changes in the riparian environment.[citation needed]
InAsia there are different types of riparian vegetation,[52] but the interactions between hydrology and ecology are similar as occurs in other geographic areas.[53]
Land clearing followed by floods can quickly erode a riverbank, taking valuable grasses and soils downstream, and later allowing the sun to bake the land dry.[54][55] Riparian zones can be restored through relocation (of human-made products), rehabilitation, and time.[44]Natural Sequence Farming techniques have been used in theUpper Hunter Valley ofNew South Wales, Australia, in an attempt to restore eroded farms to optimum productivity rapidly.[56]
The Natural Sequence Farming technique involves placing obstacles in the water's pathway to lessen the energy of a flood and help the water to deposit soil andseep into the flood zone.[57] Another technique is to quickly establishecological succession by encouraging fast-growing plants such as "weeds" (pioneer species) to grow.[58] These may spread along the watercourse and causeenvironmental degradation, but may stabilize the soil, place carbon into the ground, and protect the land from drying. The weeds will improve the streambeds so trees and grasses can return and, ideally, replace the weeds.[59][60] There are several other techniques used by government and non-government agencies to address riparian and streambed degradation, ranging from the installation of bed control structures such as log sills to the use of pin groynes or rock emplacement.[61] Other possible approaches include control of invasive species, monitoring of herbivore activity, and cessation of human activity in a particular zone followed by natural re-vegetation.[62] Conservation efforts have also encouraged incorporating the value ofecosystem services provided by riparian zones into management plans, as these benefits have traditionally been absent in the consideration and designing of these plans.[62][63]
Cottonwood Creek riparian area in southeasternOregon before restoration, 1988
Cottonwood Creek riparian area during recovery, 2000
Cottonwood Creek riparian area after restoration, 2002
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