Riparian Restoration
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Riparian Restoration By Elizabeth M. Norris* Introduction Riparian ecosystems are located on river flood- portant to the animals of the riparian ecosys- plains, and are part of the highly integrated sys- tem: (1) predominance of woody plant commu- tem that includes the stream channel. Overlap- nities, (2) presence of surface water and abun- ping terms commonly used are riparian forests, dant soil moisture, (3) diversity of interspersion riverine wetlands and riparian corridors. Ri- of habitat features, and (4) corridors for dis- parian ecosystems are connected to aquatic eco- persal and migration. In heavily farmed or ur- systems both by direct fluxes and, below-ground, ban regions, riparian areas are often the only through the hyporheic zone (Lowrance et al. wooded segments remaining. Trees and shrubs 1997). found in these buffers provide protection, roost- ing areas, and favorable microclimates for many In much of the world, riparian areas are domi- species. The riparian vegetation also shades the nated by forests. However, not all riparian zones stream, stabilizes the streambank with tree or river marginal areas are forested in their natu- roots, and produces leaf litter, all of which sup- ral condition. Even predominately forested ar- port a greater variety of aquatic life in the stream. eas may have inclusions of marshes dominated by emergent herbs, open water dominated by sub- Riparian ecosystems have many functional char- mersed plants or plankton, and unvegetated acteristics that result from the unique physical sand bars lacking trees (Brinson and Verhoeven environment. It is recognized that they are highly 1999). Only a small portion of most landscapes productive because of the convergence of energy are occupied by riparian forests and while the and materials that pass through riparian wet- contribution of these ecosystems to sustain lands in great amounts. Riparian wetlands are aquatic organisms is profound, they also have a also generally more productive than adjacent central role in sustaining a variety of terrestrial upland ecosystems because of their unique hy- organisms. drologic conditions (Mitsch and Gosselink 1993). A riparian forest buffer is an area of trees, usu- ally accompanied by shrubs and other vegeta- These shoreline landscapes concern land man- tion, that is adjacent to a body of water. Buffers agers and social scientists because they are af- are managed to maintain the integrity of stream fected by water resource developments and as- channels and shorelines. They also reduce the sociated land use (Malanson 1993). Riparian impact of upland sources of pollution by trap- areas have many values (Figure 1). Because of ping, filtering and converting sediments, nutri- their location, riparian areas were often selected ents, and other chemicals. Buffers help to ab- for early settlements. The existing waterways sorb periodic flood pulses, and to supply food, were used for transporting people and goods cover, and thermal protection to fish and other quickly and efficiently, and the water offered a wildlife. Brinson et al. (1981) described four eco- simple system for primitive waste disposal. logical attributes of forested buffers that are im- Because of these benefits, riparian areas have historically been a popular choice for urban de- *Libby Norris works for the Chesapeake Bay velopment. Expanding population centers di- Foundation as the Virginia Restoration Scientist. rectly impact stream-side lands that once sup- 1 Existing Riparian Systems Economic Values Social Values Biological Values › reduce downstream flooding › recycle nutrients, tighten spiral › special habitat for some › high yield of timber and storage endangered or threatened › recharge aquifers › store heavy metals and toxins species › surface water supply › intermediate storage for sediments › refugia for upland species › support secondary productivity › natural heritage › corridors for species (e.g. fisheries) › natural laboratories for teaching movement and research › recreation › aesthetics Former Riparian Systems ported riparian ecosystems and continually in- Economic Values crease their demands on a decidedly finite water › transport corridors supply (Patten 1998). The popularity of ripar- › water supply and electricity ian recreation sites also leaves them vulnerable › construction materials and waste disposal to over-use and misuse (Johnson and Carothers › agriculture and livestock 1982). Motorized recreation has major impacts › settlement on many riparian resources. Losses of riparian habitat are difficult to esti- Figure 1. The values of riparian ecosystems mate but are considered to be great (Malanson (Malanson 1993) 1993). Early logging operations used major wa- terways to transport large logs to downstream Wetlands Program mills, greatly impacting the shoreline ecosystem School of Marine Science and water quality. Riparian lands have suffered Virginia Institute of Marine Science catastrophic losses due to federal water projects College of William and Mary along major river systems. Mining along rivers Gloucester Point, Virginia 23062 and streams has taken its toll on the surround- (804) 684-7380 ing habitat and associated water quality. Mines can intercept the deep water table, disrupting Dr. Carl Hershner, Program Director regional aquifers and reducing stream and spring Dr. Bill Roberts, Editor flows over a large area (Nelson et al. 1991). Published by: VIMS Publication Center Mining also produces chemical contaminants that find their way into streams. This technical report was funded, in part, by the Virginia Coastal Resources Management Program Agriculture and urban development have a great of the Dept. of Environmental Quality impact on today’s riparian lands. Land devel- through Grant #NA97O20181-01 of opers generally clear large areas of shoreline to the National Oceanic and Atmospheric build homes and establish lawns. Urban resi- Administration, Office of Ocean and dences along rivers and streams are often con- Coastal Resources Management, under cerned about floods and property damage. the Coastal Zone Management Act of Therefore, flood control dams are built upstream 1972, as amended. from urban centers, which results in direct and indirect impacts on riparian habitats. Many ri- The views expressed herein are those of the parian wetlands are maintained by annual or authors and do not necessarily reflect the views semiannual flooding, especially those on the first of NOAA or any of its subagencies or DEQ. terrace above the river channel (Johnson et al. 1999). Below the reservoir, the river flow re- gime is altered and traditional riparian systems Commonwealth’s Declared Policy: “to preserve the are destroyed. Above the dam, riparian areas wetlands and to prevent their despoliation and destruc- are lost due to increased inundation and, more tion...” often, increased housing and recreational devel- Printed on recycled paper. opment around the resulting reservoir. 2 Riparian areas offer rich soils and are cleared of major geomorphic zones: (1) erosion, (2) stor- natural vegetation for agricultural development age and transport, and (3) sediment deposition. in many places. Farm landowners continue to The first two zones make up the drainage basin remove more vegetation from the edges of their and the sediment deposition (zone 3) generally cultivated fields in hopes of gaining increased occurs at the lake or ocean into which the water- crop harvest each year, thereby greatly impact- shed feeds (Mitsch and Gosselink 1993). This ing the existing buffer. Streams and rivers that is not to say that erosion does not occur in each border or cross livestock fields are often used of the zones. However, erosion rates are gener- as the primary water source and are often left ally greatest in the upper watershed (zone 1). widely available to the animals. Domestic live- Taking under consideration the effects a resto- stock concentrated in bottomlands for extended ration project would have downstream and on periods destroy riparian ground cover, destabi- the surrounding properties is an important step lize streambanks, and thus increase sediment in determining and categorizing riparian projects. loads to streams (Patten 1998). Livestock also deliver waste material high in nitrogen directly Technology tools such as remote sensing, aerial into the watersource. Each of these practices photographs and Geographic Information Sys- has contributed to the depletion of forested ri- tem (GIS) are helpful in identifying and map- parian buffers, a great loss of diverse wildlife ping riparian areas within an entire watershed. habitat, and increased erosion and nutrient run- Watershed analysis can provide a template for off into streams and rivers. restoration practitioners to use in prioritizing restoration activities. Although the analysis re- Because the benefits derived from riparian sys- quires significant time, money, and personnel, tems are provided by nature without cost, it is experience suggests that watershed analysis pro- difficult to compare the real economic worth of vides valuable direction for managing aquatic and riparian systems with activities, such as agri- riparian resources (Kershner 1997). Once a po- culture and grazing, that have well-defined mar- tential restoration site has been identified, clear ket values. In addition, these more easily quan- goals and objectives must be developed and tified activities receive subsidies that increase should be used to drive the project design. their value and encourage their development