Riparian+zones

=Riparian Zones= //by A.H.A.B. Nassam and// //V. McCoy//


 * Introduction **

The goal of this paper is to provide a brief introduction and overview of Riparian Zone. Various areas of a riparian zone provide different functions which are often the targets during restoration/reclamation projects. Before getting any further let's get familiar with the definition of the RZ; what is a riparian zone? Even though the meaning of riparian zone has been extended to accommodate an immense strip of land alongside channels (Malanson, 1993), the fundamental meaning known to the majority of the people includes only vegetation along the bed as well as banks of river channels and streams (Tanskey, 1911). The floodplain and the riparian zone are now often taken to be one and, the same entity. Riparian zones are ecological boundaries, or ecotones, that physically separate terrestrial and aquatic ecosystems (Burt T.P et al, 2002). The riparian ecotones are vital regulators of material movement through the catchment system and, thus their ecological significance and management potential has become a subject of numerous studies (Naiman and Decamps, 1990), this paper gives a great in depth description of different types of riparian zones, their functions, riparian assessments tools and techniques.


 * Here closer to home: **//Riparian ecosystem in the Southwest //

In the United States, the goal of riparian ecosystem management is to protect, restore, and compensate for previous degradation (Young K. A., 2000). Furthermore, understanding the causes of a riparian zone's degradation will assist greatly in river restorations efforts. Riparian areas are critical habitat for countless plants and animals in the arid west. There are numerous influences that have the potential in contributing to contribute to riparian zone degradation. Among them, livestock, wildfire, invasive or non-native species, such as aggressive urban development are the most physically predominant causes of riparian ecosystem degradation in the southwestern United States. Up until recently in New Mexico, livestock grazing was the leading cause of riparian degradation. Impacts to vegetation, stream and river hydrology as well as geomorphology can separately or synergistically affect stream and river function and many wildlife species (Boone K.J.OSU.edu). In New Mexico and similar areas many land uses show an absence of respect for the value of healthy and vigorous riparian ecosystems, and subsequently have resulted in the deterioration of not only riparian areas, but also the entire landscape. Generally speaking, land abuses that have degraded riparian zones include logging, water diversion for agricultural needs or municipal uses, mining roads, channelization, urbanization, industries, and irrigation. Livestock grazing has been the particular cause of ecological degradation of stream ecosystems or riparian zones in the southwest.


 * Significance of Riparian Zones **

The geomorphic template upon which the riparian forest develops is constantly undergoing change induced by the discharge regime (Brinson M.M., 1991). The drainage network from headwaters to the estuary represents a mosaic of sites that may be aggrading, degrading or maintaining a steady state (Naiman R.J. and Decamps H. 1999). Even sites in equilibrium state channels, where the downstream movement of deposited materials is balanced by the alluvial transport from upstream, will continue to meander laterally and down-valley so that the physical features of the riparian zone continue to change (Dunne T. and Leopold L.B. 1979). In riparian floodplains, having a ridge-and-swale topography, vegetative patch types alternate between those on topographic lows adapted to long hydro-periods and those on topographic highs with species also found in mesic uplands (Mertes L. et al.,1995). Most riparian zones are covered with a remarkable variety of woody vegetation from shrubs serving as refuges for small mammals to trees offering nesting and perching sites for birds. In addition, riparian forests act as refuges in adjacent areas, in some cases, as corridors for migrations and seed dispersal (Brinson M.M et al., 1981).

Multifaceted exchanges among hydrology, geomorphology, solar radiation, temperature, as well as fire influence the structure, dynamics, and composition of riparian zones/systems (Brinson M.M., 1991). (Brinson M.M., 1991)  literature suggested that hydrology, including its interactions with the local geology, is the most important factor of the riparian ecosystems. There are two particular aspects in fluvial geomorphology which help in understanding patterns and processes of riparian vegetation. These aspects include site-specific erosion and deposition, and lateral channel migration. Lateral channel migration may be slow (cm/yr) to fast (1km/yr), depending on the type of stream hydraulics, and this substantially influences the composition and demography of the vegetation communities (Brinson M.M., 1991).

Riparian vegetation modifies sediment transport either by physically entrapping materials, which appears to be most important in relatively low gradient environments, or by altering channel hydraulics. Accretion of sediment and organic matter by vegetation can be substantial, especially during flood events. Sediment supply greatly depends upon land use, climate, and tectonic activity. In addition, rates of erosion and deposition range from a couple of millimeters to several meters per year (Naiman & Decamps, 1999). Naiman and Decamps have concluded that alteration of channel hydraulics is accomplished either by roots or by large woody debris in the channel at low flows, and by stems at high flows. Woody debris and shrubs provide physical structure that slows water current, decreases the stream power,and holds materials in place. Additionally, woody debris produced by the vegetation shapes channel morphology by redirecting flows of water and sediment, sorting sediments as wells as either retaining or moving materials (Hupp C.R. and Osterkamp W.R. 1995).

Organic matter from riparian vegetation is a source of nourishment for aquatic organisms (Hynes H.B.N., 1963). It has been found that as general trend, the proportion of coarse particulate organic matter decreases as the river increases in size. The storage of coarse particulate organic matter increases during the wet season in headwater channels where retention is high, with the result that these reaches have more organic matter s than do downstream reaches. In addition to particulate organic matter, riparian zones contribute to substantial amounts of dissolved organic matter of river ecosystems. Living riparian vegetation is also a source of nourishment for numerous terrestrial animals ranging from insects to mammals. These animals can considerably alter the system function through their feeding activities. Outbreaks of defoliating insects or plants can alter riparian forest production and subsequently alter water yield, nutrient cycling, as well as stream water chemistry (Swank W.T. et al., 1981).

====Land-water interface reduces nutrient movements to streams. This process assists in understanding the role played by riparian zones in controlling nonpoint sources pollution by sediment and nutrients in agricultural watersheds (Jacobs T.C et al., 1985). While providing shelter for native as well as exotic animals, riparian vegetation also serve to armor stream banks, which help alleviate erosion burdens during spring monsoon runoffs. Vegetation reduces the flow velocity by exerting a friction or drag force on the water. A five centimeter deep root-mat could resist erosion up to 20,000 times better than bare soil stream banks, and the vigorous or dense the vegetation is, the better stream bank protection it provides (Adams and Fitch, 1995). Lana Mitchell and Meghan Preut have thoroughly described the processes of soil stabilization and protection of stream banks provided by riparian vegetation. A full rubric of riparian zone services can be found under water quality. The figure below shows a schematic of riparian zones and some of their services ====



Figure 1: Riparian zone/buffer scheme (Source: Missoula County) =**Hydrology and Importance to the Riparian Zone**= <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">High frequency of floods along most rivers and streams, and their disturbances have important effects on stream and riparian communities. This has led most riparian communities within an urban area to be moderately to highly managed by the watershed development communities. Flood pulses are regulated by the upstream catchments and are meant to keep the flooding of urban areas under control, but has led to the degradation of the natural riparian system that was dependant on these events.

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Figure 2: Hydrologic Cycle (Image Source: []<span style="font-family: Arial,sans-serif; font-size: 12pt;">) <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">The hydrology associated with most riparian zones is similar in uptake, release, and infiltration. In the Rio Grande the snow melt from the Sandia Mountains, and other watersheds that feed from the tributaries north of the Albuquerque Metro area into the Rio Grande is critical to the flow rates. The hydrographs for the watershed that feeds into the section of the river that flows through Albuquerque show that the peaks occur during snow melt runoff, as well as during the monsoon rain. This moisture is critical to the flow in the river for many reasons. The evapotranspiration of water from the canopy of trees along the bosque feeds the clouds above carrying moisture along the jetstream. As the precipitation falls, it is either infiltrated into the ground to become part of the groundwater system and recharge the aquifer, or it flows to the river for transportation down the river to Texas/Mexico. The water that flows in the channel through the Middle Rio Grande can also be uptaken into the Riparian zone for use by the riparian vegetation. The health of riparian zone vegetation is dependant upon the uptake of water from the river along with the precipitation that falls. The ground water level near the riverbanks contains a zone called the capillary fringe zone. This zone is the layer between the water saturated and unsaturated zone underground. The vegetation in most areas depend on their roots being able to reach this layer which can feed them water from the saturated zone below. The thickness of the capillary fringe zone for the continued health of the Native Cottonwood tree is 6-12 feet. For more information on hydrologic cycle see this link Hydrology.

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Figure 3: Capillary Fringe zone(Image Source: http://amybohac.wikispaces.com/Why+Your+Front+Lawn+Died<span style="font-family: Arial,sans-serif; font-size: 12pt;">)

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Riverine floodplains cover a small portion of the terrestrial and aquatic landscape; nonetheless they support high levels of environmental heterogeneity and biological diversity (Naiman et al., 1993). Floodplains are also among the most altered ecosystems in the world, thus their biological diversity continues to deteriorate at a drastic rate (Ward et al., 1999). In addition, Thoms (2003) demonstrated that floodplain development has had diverse impacts on the potential supply of dissolved organic carbon on the floodplain. Two critical factors influencing floodplain degradation are river regulation by water storage as well as diversion schemes (Dynesius and Nilsson, 1994). <span style="font-family: Arial,sans-serif; font-size: 16px;">Large floods potentially supply more dissolved organic carbon available than small floods because they inundate a larger area of the floodplain surface.
 * <span style="font-family: Arial,sans-serif; font-size: 14pt;">Degradation of Riparian Zones **

<span style="font-family: Arial,sans-serif; font-size: 12pt;">This pattern of floodplain development and channel narrowing is especially dramatic seen in many southwestern rivers of the United States in general, and in New Mexico in particular. Salt cedars (Tamarix) may have first established on bare channel margins, sandbars, and islands along the lower watershed, and vertical accretion as well as lateral expansion of these stabilized floodplains occurred over the next decades (Adam S. and Cooper D., 2006). <span style="font-family: Arial,sans-serif; font-size: 16px;">By the mid-20th century, the development of heavily vegetated floodplains mainly composed of salt cedars, often found within the active channel, forced many of these rivers and streams to narrow (Webb et al. 2004).

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Urban developments are also one of the many setbacks of floodplain welfare. Due to the convenient topography and the esthetically pleasing environment, floodplain areas appeal socio-economic activities therefore attract developers. Subsequently, these activities on the floodplain areas make s the restoration projects costly and time stressed. One the most effective ways to reduce costs of floodplain development is to restrict development activities with the floodplain areas (Zhai J. 2000). <span style="font-family: Arial,sans-serif; font-size: 12pt;">The following illustrations describe the processes of both degradation and recovery of a typical riparian system. This scheme helps visualize stream bed evolving degradation.

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Figure 2: Illustration of sequential degradation of stream (Source: USDI-BLM)

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Figure 3: Illustration of recovery of stream-associated riparian area (Source: USDI-BLM, year)


 * <span style="font-family: Arial,sans-serif; font-size: 14pt;">Invasive species **

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Although common in nature, biological invasions have been accelerated through human activities (Ledge D.M, 1993). Life-history characteristics of invaders control the various stages of establishment, stabilization as well as expansion. The richest communities also have the greatest proportion of invasive species, along the rivers and within specific sites, although several interactive processes appear to control establishment of these exotics in riparian zones (Decamps H. et al. 1995), many of them still survive and thrive. <span style="font-family: Arial,sans-serif; font-size: 12pt;">Natural environmental features may slow the rate of invasion. In addition, seed predation combined with folivores are also likely to slow the rate of expansion because the salt cedar seeds are dispersed by flotation (Naiman J. and Decamps, 1999). Although invasive species expansion can reduce native plant species diversity, there is no clear evidence supporting the fact. On the other hand, invasive exotic woody plants in arid as well as semi-arid riparian habitats such New Mexico are expected to replace or inhibit much of the native flora, but clear data supporting or rejecting these expectations do not exist as of yet (Brock J.H, 1994). <span style="font-family: Arial,sans-serif; font-size: 12pt;">One example of local invasive species is known as the Tamarisk. This tree is part of the flora and fauna that has become the very current Rio Grande. For the past few decades it has been listed as the main species threatening the existance of native species such as the Cottonwood tree. Another concern is the high groundwater use by the Tamarisk. The Tamarisk has been shown to cause a significant reduction in diurnal groundwater fluctuations even as water tables have dropped to historic lows. The Tamarisk has a fast root response to water table declines, water soil use that is very advantagous and high photosynthetic rates as well as high leaf water stress (Nippert, J.B. 2007).


 * <span style="font-family: Arial,sans-serif; font-size: 14pt;">Restoration approaches **

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Flooding through the riparian system is critical for its survival as well as its ability to thrive. Floods create heterogeneity within the riparian zone and thereby create distinct regeneration niches that facilitate the coexistence of congeneric species. Also, periodic flood disturbances of various intensities are critical for maintaining the four dominant tree species of the lowland floodplains pod carp forest as well. At local scales, floods affect species diversity of herbaceous plants through physical heterogeneities created by the erosion and or deposition of litter and silt. Ray M. has done a great job in describing the various aspects of natural flow regime which could be found by following this link <span style="font-family: Arial,sans-serif; line-height: 24px;">.

====<span style="font-family: Arial,sans-serif;">A lot of efforts have been allocated in fighting undesirable invasive species, especially here in New Mexico. Millions of dollars and man hours have been invested in controlling these exotic plant andvarious methods are being utilized to control these <span style="color: #000000; font-family: Arial,sans-serif; font-size: 17px; line-height: 22px;">invaders <span style="font-family: Arial,sans-serif;">. For example, in the Middle Rio Grande and some other parts of the region, goats and foreign beetles are being used to eliminate the salt cedars. ====

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Levees support riparian gallery forests that otherwise may flood frequently, however, the coarse deposits normally result in rapid drainage when water levels drop. Oxbow lakes are the most hydric of the riparian habitats, supporting species adapted to constant flooding and anaerobic soils (Naiman R.J. and Decamps H., 1999).

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Though construction of levees and dams is one of various approaches utilized in stream restoration efforts, ironically, their removal has been undertaken for the same stream restoration reasons. Dam removals started back in the 1990's and these endeavors were undertaken to not only remove the ones that pose security risks, but also dams that are in violation of the endangered species act. More about dams and other types of impoundments can be found through L. Pickel’s paper by clicking here.


 * <span style="font-family: Arial,sans-serif; font-size: 14pt;">Examples of restoration projects **

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Many stream restoration projects have been carried out worldwide in general and in the southwest of the United States in particular. The majority of these restoration works are undertaken to address issues pertaining to bank stabilization and re-vegetation in order to control excessive erosion due to soil instability or storm runoff. Some restoration projects are geared towards the removal of non-native invasive plant species (example of Saltceadar and Russian Olive in New Mexico) and re-vegetation (active or passive) of native riparian vegetation, while others are done to modify the existing land form to allow a stream to regain its historic connection to its floodplain.

//<span style="font-family: Arial,sans-serif; font-size: 12pt;">Example of Rio Grande //<span style="font-family: Arial,sans-serif; font-size: 12pt;">:

<span style="font-family: Arial,sans-serif; font-size: 12pt;">The restoration project on the 45 km Cochiti reach of the Middle Rio Grande is a perfect case study of an alluvial river restoration in response to natural and anthropogenic alteration to flows (Gigi and Pierre, 2003). Alteration in water due to diversions and dams as well as sediment regime of Rio Grande following the construction of Cochiti Dam, and the resulting channel adjustments both vertically and laterally, have altered the riparian and aquatic systems causing various issues. These issues include retardation of regeneration of native cottonwood forest which is affected by intrusion of invasive plants. In addition, floodplains are disconnected from the river channel causing them to remain dry during periods of peak flow. Also, Channel platform changes shrank the available habitat for the silvery minnows.



<span style="font-family: Arial,sans-serif; font-size: 12pt;">Figure 4: Map showing the restoration location <span style="font-family: Arial,sans-serif; font-size: 16px;">(Richard, 2001)



<span style="font-family: Arial,sans-serif; font-size: 12pt;">Figure 5: Platform adjustments of Cochiti Reach, Rio Grande (Richard, 2001)

<span style="font-family: Arial,sans-serif; font-size: 12pt;">In an effort to remediate the issue mentioned above, the State of New Mexico carried out restoration work which specifically targeted the removal and eradication of exotic plants. This helped lower the floodplains which in turn allowed them not only to be inundated during high flows, but also facilitated channel widening which increased habitat diversity within the channel.


 * <span style="font-family: Arial,sans-serif; font-size: 14pt;">Conclusion: **

<span style="font-family: Arial,sans-serif; font-size: 12pt;">Even though the riparian zone is a complex system, understanding its processes is imperative in order to maximize the services it provides to us, and to all the various plants and animals living in or around it. Over the years, due to anthropogenic or natural events or sometimes both, riparian zones have become degraded, and thus incapable of fully or perpetually performing functions. Restoration and or reclamation projects are carried out in order to fix these problems. To achieve a successful restoration project, a thorough stream assessment is imperative in order to properly tackle the issues. Since stream morphology differs from one system to another, restoration projects should be carried out on a stream to stream basis using adaptive management approach.


 * <span style="font-family: Arial,sans-serif; font-size: 14pt;">References **

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