Riparian buffers are vegetated, often forested, areas (“strips”) adjacent to streams, rivers, lakes and other waterways protecting aquatic environments from the impacts of surrounding land use (Enanga et al. 2010). Use of riparian buffers to maintain water quality in streams and rivers is considered to be a best forest and conservation management practice in many countries and is mandatory in some areas.
Riparian buffers help to maintain water quality in waterways by protecting streams from non-point source pollution (e.g. from surrounding agricultural activities). Riparian vegetation cover prevents sediments, as well as such pollutants as nitrogen, phosphorus and others from entering water through biological (e.g. nutrient uptake by riparian vegetation) and physical-chemical (e.g. nutrient absorption for phosphorus which binds to clay particles and sediments) processes (Enanga et al. 2010).
Vegetation and tree roots also stabilize banks and prevent erosion. During flood events, riparian vegetation slows down runoff by absorbing excess water, reduces peak flow and helps to mitigate potential flood damage downstream (Colgan et al. 2013). Such buffer strips also yield benefits in agricultural areas, both by retaining sediment and nutrients from entering the waterways, thereby preventing water pollution, and maintaining soil productivity on the fields (Schmidt and Batker 2012). Some studies show that riparian buffers can help to reduce the amount of sediment reaching the streams by as much as 80 per cent (Crétaz and Barten 2007).
Trees also provide shade and reduce water temperature fluctuations, which is an important factor for the survival of many aquatic species. Shade provided by riparian vegetation also contributes to maintaining water quality, as high levels of light leads to increases in in-stream primary production, and can change the invertebrate species composition (Parkyn 2004). Increases in summer water temperatures can increase anoxia in stratified lakes, elevate the rate of phosphorus releases from lake and slow moving river sediments and cause algal blooms (Whitehead et al. 2009). Together with changes in actual water flows that affect riparian vegetation and water biota, the combined factors can impact on riparian food webs (Covich et al. 1999). A recent study in Denmark found that relatively short stretches (100–500 m) of riparian forest combat the negative effects of heating of stream water (Kristensen et al. 2013).
Depending on the extent and the type of vegetation in the riparian buffers, they can provide important biodiversity benefits. Vegetation provides biodiversity habitat for many species, that in some cases can be particularly beneficial for agricultural activities via insects and birds that facilitate pollination of the fields. The cover and shade also provide favourable conditions for birds and other animals that can take refuge in the buffer zones, and which use the riparian buffer zones as corridors for movement. This is important for pastoralist communities that often rest animals in riparian areas for watering, grazing and protection. Riparian vegetation, either designed or natural, is sometimes referred to as “shelterbelts” and offer shade and weather protection (due to cooling effects). They also reduce wind velocities, dust (including air pollutants) and erosion (Bird et al. 1992; Bird 1998; Heath et al. 1999).
In addition, riparian buffers can offer aesthetic and recreation value to nearby communities (Schmidt and Batker 2012). Drought, however, can weaken the resilience of intact riparian vegetation and larger forest ecosystems to pests and disease (Anderson 2008). The falling leaves and debris in turn provide food for aquatic species (Parkyn 2004). Moreover, water systems containing too many dead leaves and stored organic matter can become hypoxic, with decreased pH and fairly high concentrations of tannin and lignin, making the water toxic to fish and other aquatic species (Gehrke et al. 1993; Bond et al. 2008).
Costs associated with establishment and conservation of riparian buffer strips include land acquisition and any associated foregone economic opportunity, and when necessary, the planting of buffer zones. Where riparian land is on private property, public investment may need to be made for land acquisition or economic incentives for private landowners to establish riparian buffers.