Riparian zone

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A well maintained Riparian strip on a tributary to Lake Erie.

Riparian zone is the interface between land and a flowing surface water body. They are typically characterized by hydrophilic vegetation and are often subject to flooding. Riparian zones are significant in ecology, environmental management and civil engineering due to their role in soil conservation, their biodiversity and the influence they have on aquatic ecosystems. Riparian zones occur in many forms including grassland, woodland, wetland or even non-vegetative. In some regions the terms riparian woodland, riparian forest, riparian buffer zone or riparian strip are used to characterize a riparian zone.

Riparian zones may be natural or engineered for soil stabilization or restoration. These zones are important natural biofilters, protecting aquatic environments from excessive sedimentation, polluted surface runoff and erosion. They supply shelter and food for many aquatic animals and shade that is an important part of stream temperature regulation. When riparian zones are damaged by construction, agriculture or silvaculture, biological restoration can take place, usually by human intervention in erosion control and revegetation. If the area adjacent to a watercourse has standing water or saturated soil for as long as a season, it is normally termed a wetland due to its hydric soil characteristics.

Research shows riparian zones are instrumental in water quality improvement for both surface runoff and water flowing into streams through subsurface or groundwater flow. Particularly the attenuation of nitrate or denitrification of the nitrates from fertilizer in this buffer zone is important. Riparian zones can play a role in lowering nitrate contamination in surface runoff from agricultural fields, which runoff would otherwise have a negative effect on ecosystem and human health. 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.

Contents

1 Roles and functions
2 Role in logging
3 Vegetation
4 References
5 See also
6 External links

Roles and functions

A riparian zone schematic from the Everglades.

Some of the important functions of riparian zones are:

Dissipate stream energy: Meandering curves of a river, combined with vegetation and root systems dissipate stream energy, resulting in less soil erosion and a reduction in flood damage.
Trap sediment: Reduce suspended sediments creates less turbid water and replenishes soils and build stream banks.
Filter pollutants from surface runoff and enhance water quality.
Provide wildlife habitat, increase biodiversity and forage for wildlife and livestock.
Provide wildlife corridors: enable aquatic and reparian organisms to move along river systems avoiding isolated communities.
Provide native landscape irrigation by extending seasonal or perennial flows of water.

Role in logging

Protecting riparian zones are often included in logging operations. The undisturbed soil, soil cover, and vegetation provide shade, leaf litter, woody material, and reduce the delivery of soil eroded from the harvested area. Factors such as soil types and root structures, climatic conditions and above ground vegetative cover have a major bearing as to the effectiveness of riparian buffering.

Vegetation

The assortment of riparian zone trees varies from those of wetlands and typically consists of plants that either are emergent aquatic plants, or herbs, trees and shrubs that thrive in proximity to water. Typical riparian zone trees in the eastern United States include:

Cottonwood, Populus deltoides
Silver maple, Acer saccharinum
Boxelder, Acer negundo
American elm, Ulmus americana
American sycamore, Platanus occidentalis
Butternut, Juglans cinerea
Black walnut, Juglans nigra
Black willow, Salix nigra
River birch, Betula nigra
Green ash, Fraxinus pensylvanica
Honey locust, Gleditsia triacanthos
Basswood, Tilia americana

In the western United States riparian vegetation may include red willow, grasses, sedges and wingstem.

References

Nakasone, H., Kuroda, H., Kato, T. and Tabuchi, T. (2003). Nitrogen removal from water containing high nitrate nitrogen in a paddy field (wetland). Water Science and Technology, vol.48, no.10, pp.209-216.
Mengis, M., Schiff, S.L., Harris, M., English, M.C., Aravena, R., Elgood, R.J., and MacLean, A. (1999). Multiple geochemical and isotopic approaches for assessing ground water NO3 elimination in a riparian zone. Ground Water, 37, 448-457.
Parkyn, Stephanie. (2004). Review of Riparian Buffer Zone Effectiveness. Ministry of Agriculture and Forestry (New Zealand), www.maf.govt.nz/publications.
Tang, Changyuan; Azuma, Kazuaki; Iwami, Yoshifumi; Ohji, Baku; Sakura, Yasuo. (2004). Nitrate behaviour in the groundwater of a headwater wetland, Chiba, Japan. Hydrological Processes, vol.18, no.16, pp.3159-3168.

External links