Riparian zone / REF / 755 / 2014

A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the fifteen terrestrial biomes of the earth. Plant habitats and communities along the river margins and banks are called riparian vegetation, characterized by hydrophilic plants. Riparian zones are significant in ecology, environmental management, and civil engineering because of their role in soil conservation, their habitat biodiversity, and the influence they have on fauna and aquatic ecosystems, 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. The word "riparian" is derived from Latin ripa, meaning river bank.

Characteristics

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 silviculture, 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 because of its hydric soil characteristics. Because of their prominent role in supporting a diversity of species, riparian zones are often the subject of national protection in a Biodiversity Action Plan. These also known as a "Plant or Vegetation Waste Buffer".

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 damage ecosystems 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.

Roles and functions

Riparian zones dissipate stream energy. The meandering curves of a river, combined with vegetation and root systems, dissipate stream energy, which results in less soil erosion and a reduction in flood damage. Sediment is trapped, reducing suspended solids to create less turbid water, replenish soils, and build stream banks. Pollutants are filtered from surface runoff which enhances water quality via biofiltration.

The riparian zones also provide wildlife habitat, increased biodiversity, and provide wildlife corridors, enabling aquatic and riparian organisms to move along river systems avoiding isolated communities. They can provide forage for wildlife and livestock.

They provide native landscape irrigation by extending seasonal or perennial flows of water. Nutrients from terrestrial vegetation (e.g. plant litter and insect drop) is transferred to aquatic food webs. The vegetation surrounding the stream helps to shade the water, mitigating water temperature changes. The vegetation also contributes wood debris to streams which is important to maintaining geomorphology.

From a social aspect, riparian zones contribute to nearby property values through amenity and views, and they improve enjoyment for footpaths and bikeways through supporting foreshoreway networks. Space is created for riparian sports including fishing, swimming and launching for vessels and paddlecraft.

The riparian zone acts as a sacrificial erosion buffer to absorb impacts of factors including climate change, increased runoff from urbanisation and increased boatwake without damaging structures located behind a setback zone.

Role in logging

The protection of riparian zones is often a consideration in logging operations. The undisturbed soil, soil cover, and vegetation provide shade, plant 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 impact 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.

North America

Water's edge

Herbaceous Perennial:

• Peltandra virginica – Arrow Arum
• Sagittaria lancifolia – Arrowhead
• Carex stricta – Tussock Sedge
• Iris virginica – Southern Blue Flag Iris

Inundated Riparian zone

Herbaceous Perennial:

• Sagittaria latifolia – Duck Potato
• Schoenoplectus tabernaemontani – Softstem Bulrush
• Scirpus americanus – Three-square Bulrush
• Eleocharis quadrangulata – Square-stem Spikerush
• Eleocharis obtusa – Spikerush

Western

In western North America and the Pacific Coast the riparian vegetation includes: Riparian trees

• Sequoia sempervirens – Coast Redwood
• Thuja plicata – Western Redcedar
• Abies grandis – Grand Fir
• Picea sitchensis – Sitka Spruce
• Chamaecyparis lawsoniana – Port Orford-cedar
• Taxus brevifolia – Pacific Yew
• Populus fremontii – Fremont Cottonwood
• Populus trichocarpa – Black Cottonwood
• Platanus racemosa – California Sycamore
• Alnus rhombifolia – White Alder
• Alnus rubra – Red Alder
• Acer macrophyllum – Big-leaf Maple
• Fraxinus latifolia – Oregon ash
• Prunus emarginata – Bitter Cherry
• Salix lasiolepis – Arroyo Willow
• Salix lucida – Pacific Willow
• Quercus agrifolia – Coast live oak
• Quercus garryana – Garry oak
• Populus tremuloides – Quaking Aspen
• Umbellularia californica – California Bay Laurel
• Cornus nuttallii – Pacific Dogwood

Riparian shrubs

• Acer circinatum – Vine Maple
• Ribes spp. – Gooseberies and Currants
• Rosa pisocarpa – Swamp Rose or Cluster Rose
• Symphoricarpos albus – Snowberry
• Spiraea douglasii – Douglas spirea
• Rubus spp. – Blackberries, Raspberries, Thimbleberry, Salmonberry
• Rhododendron occidentale – Western Azalea
• Oplopanax horridus – Devil's Club
• Oemleria cerasiformis – Indian Plum, Osoberry
• Lonicera involucrata – Twinberry
• Cornus stolonifera – Red-osier Dogwood
• Salix spp. – Willows

Other plants

• Polypodium – Polypody Ferns
• Polystichum – Sword Ferns
• Woodwardia – Giant Chain Ferns
• Pteridium – Goldback Ferns
• Dryopteris – Wood Ferns
• Adiantum – Maidenhair Ferns
• Carex spp. – Sedges
• Juncus spp. – Rushes
• Festuca californica – California Fescue bunchgrass
• Leymus condensatus – Giant Wildrye bunchgrass
• Melica californica – California Melic bunchgrass
• Mimulus spp. – Monkeyflower and varieties
• Aquilegia spp. – Columbine

Asia

In Asia there are different types of riparian vegetation, but the interactions between hydrology and ecology are similar as occurs in other geographic areas.

• Carex spp. – Sedges
• Juncus spp. – Rushes

Australia

Typical riparian vegetation in Temperate New South Wales, Australia include:

• Acacia melanoxylon – Blackwood
• Acacia pravissima – Ovens Wattle
• Acacia rubida – Red Stem Wattle
• Bursaria lasiophylla – Blackthorn
• Callistemon citrinus – Crimson Bottlebrush
• Callistemon sieberi – River Bottlebrush
• Casuarina cunninghamiana – River She-Oak
• Eucalyptus bridgesiana – Apple Box
• Eucalyptus camaldulensis – River Red Gum
• Eucalyptus melliodora – Yellow Box
• Eucalyptus viminalis – Manna Gum
• Kunzea ericoides – Burgan
• Leptospermum obovatum – River Tea-Tree
• Melaleuca ericifolia – Swamp Paperbark

Central Europe

Typical riparian zone trees in Central Europe include:

• Acer campestre – Field Maple
• Acer pseudoplatanus – Sycamore Maple
• Alnus glutinosa – Black Alder
• Carpinus betulus – European Hornbeam
• Fraxinus excelsior – European Ash
• Juglans regia – Persian Walnut
• Malus sylvestris – European Wild Apple
• Populus alba – White Poplar
• Populus nigra – Black Poplar
• Quercus robur – Pedunculate Oak
• Salix alba – White Willow
• Salix fragilis – Crack Willow
• Tilia cordata – Small-leaved Lime
• Ulmus laevis – European White Elm
• Ulmus minor – Field Elm

Repair and restoration

Land clearing followed by floods can quickly erode a riverbank, taking valuable grasses and soils downstream, and allowing the sun to bake the land dry. Natural Sequence Farming techniques have been used in the Upper Hunter Valley of New South Wales, Australia to rapidly restore eroded farms to optimum productivity.

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 and seep into the flood zone. Another technique is to quickly establish ecological succession by encouraging fast growing plants such as "weeds" (pioneer species) to grow. These can quickly stabilize the soil, place carbon into the ground, and protect the land from drying. The weeds will improve the streambeds so that trees and grasses can return, and later replace the weeds.

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  Terrestrial biomes

  Conservation

  Hydrology

  Water streams

  Rivers

  Habitats

  Habitat

  Water and the environment

  Freshwater ecology