A riparian zone is the interface between land and water bodies, including streams, rivers, lakes and estuarine marine shores. Riparian zones can therefore be considered as a transitional belt between terrestrial and aquatic ecosystems and are distinguished by gradients in biophysical conditions, ecological processes and biota (National Research Council, U.S, 2002). Naiman, Decamps, and McClain (2005) defined riparian zones as transitional semi-terrestrial areas regularly influenced by fresh water, normally extending from the edges of water bodies to edges of upland communities.
It is important to note that the riparian vegetation acts as a buffer zone along rivers and lake shores in various ways. It may minimise the effects from river spates, e.g. the water flowing from upstream reaches downstream through absorption, hence causing stability in the water flow. Furthermore, the vegetation usually traps sediment and therefore influences sedimentation downstream.
A riparian zone is often a habitat for rare species and it is also a breeding ground for aquatic fauna such as fish and invertebrates (Naiman et al., 2005). Loss of riparian vegetation can decrease the amount of suitable habitat for riparian and aquatic fauna such as fish and invertebrates, thereby reducing stream productivity and fish carrying capacity (Karen, M. & Karen, S., 1998). Riparian vegetation has many critical functions; it provides resistance to flowing water as well as to runoff during floods. The vegetation provides protective cover which helps to absorb the forces exerted by flowing water (Watson & Basher, 2006). Riparian plant canopies intercept, store and evaporate a portion of precipitation and have an important role in influencing stream temperature and the health of aquatic species (National Research Council, U.S., 2002).
Soils found in riparian zones have pronounced spatial variability in structure, particle size distribution and other properties, not only across the riparian area but also vertically within the given soil profile. This is dependent on soil geological formation and the landscape of the area. Soil properties and the microtopography of the valley floor affect the biotic composition of the riparian community (Naiman, Bilby & Bisson, 2000) and hence their biodiversity.
The structure and function of the riparian zone are highly influenced by climate through temperature, precipitation, evaporation and runoff. Floods play a significant role in determining regeneration from seed as well as long term seedling survival. Soil moisture and depth to the water table also influence the composition of the riparian plant communities (Naiman et al., 2005).
Riparian areas supply water for domestic and agricultural uses, forage, and browse for native herbivores, livestock and recreational opportunities. The riparian areas are so important that they have been extensively and intensively used for decades by humans for a variety of purposes that range from providing well-vegetated sites for grazing to places of beauty and solace that renew the spirit of visitors (Chambers & Miller, 2004).
Degradation of riparian zones is a result of complex interrelated responses from geomorphic, hydrologic and biotic processes to climate change and natural and anthropogenic disturbances (Chambers & Miller, 2004). The disturbances can alter the hydrological or sediment regime of the river/stream system and produce changes in the physical properties of riparian ecosystems such as stream channel characteristics, and surface and ground water interactions. Human activities such as agriculture, harvesting of riparian flora and hunting of riparian fauna, grazing and industrial discharges have a great impact on riparian ecosystems. Direct discharge of untreated waste from industries, domestic and urban sources into lakes contribute to various forms of pollution, eutrophication, suspended solids, sedimentation and pesticide residues leached from soils and agricultural plantations (Odadal et al., 2003). Human impact such as dams, deforestation and water use practices pose serious threats to water availability to downstream populations (United States Agency for International Development, 2008). Degradation of riparian zones not only affects the riparian area but also the surface and ground water resources and the aquatic fauna and flora; and the terrestrial ecosystem. Thus, the riparian zone is increasingly seen as ecologically important in landscapes, and identification of the boundaries of such areas is important and has clear management significance (Nally, Molyneux, Thomson, Lake & Read, 2008).