Shoreline Stewardship

IV. B. 9. Marine Riparian Zones

Riparian zones are those areas on or by land bordering a stream, lake, tidewater, or other body of water (Hall 1987) that constitute the interface between terrestrial and aquatic ecosystems (Levings and Jamieson 2001) (Figure IV-10).  They perform a number of vital functions that affect the quality of aquatic and terrestrial habitats as determined by their physical, chemical and biological characteristics. Riparian-aquatic interactions are now recognized by scientists as so important that riparian buffers have been established as a central element of forest practice rules and watershed restoration efforts (Spence et al. 1996; Knutson and Naef 1997).  Riparian vegetation composition, density, and continuity are some of the most important characteristics of riparian systems (Table IV-9).

Figure IV-10. Riparian zone in Seabold area(Source: Applied Environmental Sciences, Inc.)

Most of what we know about riparian functions and values comes from investigations of freshwater systems, which have been the subject of extensive research (Knutson and Naef 1997).  Although marine riparian zones have not been subject to the same level of scientific investigation, increasing evidence suggests that riparian zones serve similar functions regardless of the salinity of the water bodies they border (Desbonnet et al. 1994), and are likely to provide additional functions unique to nearshore systems (Brennan and Culverwell in prep). For example, besides providing shade for forage fish spawn, insects produced in the vegetation may be an important source of prey to juvenile salmon and other fish in the nearshore area (Levings and Jamieson 2001).  Levings and Jamieson (2001) list as other functions wave energy absorption and provision of structure.

Trees and woody debris derived from the marine riparian zone may serve as shelter for fish and invertebrates at all levels of the intertidal zone.  They recommend that the value of marine riparian habitat should include consideration of the ability to 1) provide shade, 2) supply and/or filter shore derived sediment, 3) stabilize shorelines, and 4) filter and mineralize non-point organic pollutants such as nitrogen from septic fields. 

Marine riparian vegetation provides a buffer analogous to freshwater systems (Desbonnet et al. 1994).  Castelle et al. (1994) shows that buffers protect adjacent habitats, such as wetlands.  Among the functions listed are moderating the effects of stormwater runoff and soil erosion; filtering suspended solids, nutrients, and harmful or toxic substances; and moderating water level fluctuations.  Buffers provide essential habitat for wetland-associated species for use in feeding, roosting, and breeding and rearing young, and provide safe cover for mobility and thermal protection.  Buffers with dense vegetation cover on slopes less than 15% are most effective in treating runoff from upland areas.  Dense shrub and forested vegetation with steep slopes provide the greatest protection from direct human disturbance.  Castelle et al. (1994) reveals that as buffer width increases the effectiveness of removing sediments, nutrients, bacteria, and other pollutants from surface water increases.  Furthermore, buffers of less than 50 feet in width are generally ineffective in protecting wetlands.  To protect important wetland functions, buffer width on the order of 100 to 300 feet is required.  The national review by Desbonnet et al. (1994) of coastal buffers indicates that functional effectiveness increases substantially with high quality buffers at least 75 m (246 feet) in width. 

Land clearing occurs with most development projects, including those at the waters edge.  Over time, vegetation has been removed for timber, housing and other land development, roads, railroads, port and other commercial and industrial development, view corridors, shoreline armoring, landscaping, beach access, and other land-use practices.  Vegetation removal and the introduction of exotic species change community structure, increase the chance of competitive interactions, change soil chemistry and microclimate, and increase solar and wind exposure; thereby altering the functions of the marine riparian zone.  Some local governments provide limited guidelines for the removal of vegetation in their Shoreline Master Programs, but most regulators admit it is extremely difficult to enforce (Broadhurst 1998) and regulations and enforcement have been woefully inadequate to protect this critical element of the nearshore ecosystem (Brennan and Culverwell in prep).