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Stream restoration is often performed to reduce the effects of stressors on the environment and return stream structure and function to pre-disturbance conditions. Often, restoration projects aim to improve water quality and in-stream habitat, manage riparian zones, stabilize stream banks, and allow fish to pass barriers. Stream restorations are commonly carried out across the United States, although very few studies have assessed and monitored the long-term effects of restoration; thus, the outcomes of stream restorations are generally not well documented. Of the many possible stream restoration approaches, one prominent approach in low-gradient, sandy-bottomed streams is the addition of coarse woody debris (CWD) to improve in-stream habitat. In an experimental study summarized here, debris dams were added to 4 streams at Fort Benning Military Installation, Georgia, to mitigate the impacts of military training activities. Results were compared to 4 control streams that were not restored. There were some short-term (< 3 y) changes to stream ecosystem structure and function, but thus far, minimal long-term (~14 y) effects on these streams have been evident.
 
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'''CONTRIBUTOR(S):'''  
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'''CONTRIBUTOR(S):''' [[Dr. Natalie Griffiths]], [[Dan Isenberg]], [[Sam Bickley]], [[Dr. Brian Helms]], and [[Dr. Jack Feminella]]
  
 
'''Key Resource(s)''':
 
'''Key Resource(s)''':
 +
*[https://doi.org/10.1126/science.1109769 Synthesizing US River Restoration Efforts]<ref name= "Bernhardt2005">Bernhardt, E.S., Palmer, M.A., Allan, J.D., Alexander, G., Barnas, K., Brooks, S., Carr, J., Clayton, S., Dahm, C., Follstad-Shah, J. and Galat, D., 2005. Synthesizing US river restoration efforts. Science. Vol. 308, Issue 5722, pp. 636-637. [https://doi.org/10.1126/science.1109769  doi: 10.1126/science.1109769]</ref>
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*[[media:2006-Mulholland-Riparian_Ecosystem_Mgmt_at_Miitary_Installations.pdf| Riparian Ecosystem Management at Military Installations: Determination of Impacts and Evaluation of Restoration and Enhancement Strategies]]<ref name= "Mulholland2007">Mulholland, P.J., Feminella, J.W., Lockaby, B.G. and Hollon, G.L., 2007. Riparian Ecosystem Management at Military Installations: Determination of Impacts and Evaluation of Restoration and Enhancement Strategies. Final Technical Report SI-1186. Pp.161. [[media:2006-Mulholland-Riparian_Ecosystem_Mgmt_at_Miitary_Installations.pdf| Report.pdf]]</ref>
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*[https://doi.org/10.17226/1807 Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy]<ref name = "NRC1992">National Research Council, 1992. Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy. National Academies Press. [https://doi.org/10.17226/1807 doi: 10.17226/1807]</ref>
 +
*[https://doi.org/10.1577/M06-169.1 Global Review of the Physical and Biological Effectiveness of Stream Habitat Rehabilitation Techniques]<ref name= "Roni2008">Roni, P., Hanson, K. and Beechie, T., 2008. Global review of the physical and biological effectiveness of stream habitat rehabilitation techniques. North American Journal of Fisheries Management, 28(3), pp.856-890. [https://doi.org/10.1577/M06-169.1 doi: 10.1577/M06-169.1]</ref>
 +
 +
==Stream Restoration: Definitions and Scope==
 +
Stream restoration is an overarching term used to describe the process of returning stream structure and function to pre-disturbance conditions<ref name = "NRC1992"/>. This definition of “restoration” differs from “reclamation” and “rehabilitation” in that the latter two terms describe altering a system to meet various human needs<ref name = "NRC1992"/>. Stream restorations often focus on improving the ecological condition within the stream itself, but it is important to recognize that streams are part of larger watersheds, with both upstream-downstream and lateral connections (i.e., to riparian zones and floodplains<ref name = "NRC1992"/>. Therefore, small-scale, in-stream restorations may have little impact if larger-scale impacts (e.g., land disturbances) are not addressed<ref name = "NRC1992"/><ref name= "Craig2008"/> Craig, L.S., Palmer, M.A., Richardson, D.C., Filoso, S., Bernhardt, E.S., Bledsoe, B.P., Doyle, M.W., Groffman, P.M., Hassett, B.A., Kaushal, S.S. and Mayer, P.M., 2008. Stream restoration strategies for reducing river nitrogen loads. Frontiers in Ecology and the Environment, 6(10), pp.529-538. [https://doi.org/10.1890/070080 doi: 10.1890/070080]</ref><ref name= "Roni2008"/><ref name= "Bernhardt2011>Bernhardt, E.S. and Palmer, M.A., 2011. River restoration: the fuzzy logic of repairing reaches to reverse catchment scale degradation. Ecological applications, 21(6), pp.1926-1931. [https://doi.org/10.1890/10-1574.1 doi: 10.1890/10-1574.1]</ref>. Instead, watershed-scale approaches focusing on improving land management practices within the watershed and also applying multiple, complementary stream and riparian restoration approaches have been recommended<ref name = "NRC1992"/><ref name = "Palmer2005">Palmer, M.A., Bernhardt, E.S., Allan, J.D., Lake, P.S., Alexander, G., Brooks, S., Carr, J., Clayton, S., Dahm, C.N., Shah, J.F. and Galat, D.L., 2005. Standards for ecologically successful river restoration. Journal of applied ecology, 42(2), pp.208-217. [https://doi.org/10.1111/j.1365-2664.2005.01004.x doi: 10.1111/j.1365-2664.2005.01004.x]</ref><ref name= "Craig2008"><ref name= "Bernhardt2011/>).
 +
 +
As an example, Roni et al. (2002)<ref name= "Roni2002">Roni, P., Beechie, T.J., Bilby, R.E., Leonetti, F.E., Pollock, M.M. and Pess, G.R., 2002. A review of stream restoration techniques and a hierarchical strategy for prioritizing restoration in Pacific Northwest watersheds. North American Journal of Fisheries Management, 22(1), pp.1-20. [https://doi.org/10.1577/1548-8675(2002)022<0001:AROSRT>2.0.CO;2 doi: 10.1577/1548-8675(2002)022<0001:AROSRT>2.0.CO;2]</ref> presented a hierarchical approach for restoration, with this approach specifically developed for improving fish habitat in forests and rangelands. They suggested that managers prioritize protecting intact (i.e., non-degraded) stream reaches that have high-quality habitat for fishes. Subsequent efforts should then focus on reconnecting high-quality habitats that have been disconnected hydrologically, followed by restoring ecosystem processes (e.g., restoring riparian processes by livestock exclusion), and lastly focusing on improving in-stream habitat through habitat augmentation practices (e.g., large wood or boulder additions).
 +
 +
==Stressors to stream ecosystems that motivate restoration==
 +
Headwater streams are important components of river networks and, like most waterways, they are also vulnerable to degradation from anthropogenic and natural sources<ref>US Environmental Protection Agency (USEPA), 2006. Wadeable Streams Assessment: A Collaborative Survey of the Nation's Streams. EPA. Office of Research and Development, Office of Water, Washington DC 20460. EPA 841-B-06-002. [[media:2006-USEPA-Wadeable_Streams_Assessment.pdf| Report.pdf]]</ref>. Because of their close hydrologic connection to the surrounding terrestrial environment, headwater streams can be particularly influenced by land disturbances<ref>Allan, J.D., 2004. Landscapes and riverscapes: the influence of land use on stream ecosystems. Annu. Rev. Ecol. Evol. Syst., 35, pp.257-284. [https://doi.org/10.1146/annurev.ecolsys.35.120202.110122 doi: 10.1146/annurev.ecolsys.35.120202.110122]</ref><ref name= "Maloney2005">Maloney, K.O., Mulholland, P.J. and Feminella, J.W., 2005. Influence of catchment-scale military land use on stream physical and organic matter variables in small southeastern plains catchments (USA). Environmental Management, 35(5), pp.677-691. [http://dx.doi.org/10.1007/s00267-005-8651-5 doi: 10.1007/s00267-005-8651-5]</ref><ref>Walsh, C.J., Roy, A.H., Feminella, J.W., Cottingham, P.D., Groffman, P.M. and Morgan, R.P., 2005. The urban stream syndrome: current knowledge and the search for a cure. Journal of the North American Benthological Society, 24(3), pp.706-723. [https://doi.org/10.1899/04-028.1 doi: 10.1899/04-028.1]</ref>. Further, the hydrologic connectivity of river networks means that disturbances in headwaters can influence downstream ecosystems<ref>Rabalais, N.N., Turner, R.E. and Wiseman Jr, W.J., 2002. Gulf of Mexico hypoxia, aka “The dead zone”. Annual Review of ecology and Systematics, 33(1), pp.235-263. [https://doi.org/10.1146/annurev.ecolsys.33.010802.150513 doi: 10.1146/annurev.ecolsys.33.010802.150513]</ref>. Thus, minimizing human impacts in headwater streams is important not only for protecting these ecosystems and their biodiversity but also because of the multiple services they provide to downstream ecosystems (e.g., water for drinking, bathing, recreation, consumption of fish, etc.).
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A survey of stream restorations in the southeastern US revealed that environmental degradation, mitigation, and public safety were the main factors motivating stream restorations<ref name= "Sudduth2007">Sudduth, E.B., Meyer, J.L. and Bernhardt, E.S., 2007. Stream restoration practices in the southeastern United States. Restoration Ecology, 15(3), pp.573-583. [https://doi.org/10.1111/j.1526-100X.2007.00252.x doi: 10.1111/j.1526-100X.2007.00252.x]</ref>. Environmental stressors include changes in land use (e.g., forestland conversion) and hydrology (e.g., water withdrawals) in the surrounding watershed<ref>Stanford, J.A., Ward, J.V., Liss, W.J., Frissell, C.A., Williams, R.N., Lichatowich, J.A. and Coutant, C.C., 1996. A general protocol for restoration of regulated rivers. Regulated Rivers: Research & Management, 12(4‐5), pp.391-413. [https://doi.org/10.1002/(SICI)1099-1646(199607)12:4/5<391::AID-RRR436>3.0.CO;2-4 doi: 10.1002/(SICI)1099-1646(199607)12:4/5<391::AID-RRR436>3.0.CO;2-4]</ref><ref name= "Bernhardt2011/>. These factors, in turn, can reduce water quality, alter water quantity, degrade in-stream habitat and associated aquatic biodiversity, and alter availability and quality of food resources for biota (e.g., organic matter inputs<ref name = "NRC1992"/>). Therefore, the five most common goals of stream restoration projects are:
 +
 +
*improve water quality;
 +
*manage riparian zones;
 +
*improve in-stream habitat;
 +
*allow for fish passage and
 +
*stabilize stream banks<ref name= "Bernhardt2005"/>
 +
 +
==Restoration goals and assessment of efficacy: the importance of monitoring==
 +
Identification of a restoration project’s mission, goals, and objectives is necessary in order to evaluate the ecological success of that restoration<ref name = "NRC1992"/><ref name = "Palmer2005"/>. Central to this approach is the implementation of pre-restoration and post-restoration monitoring at appropriate spatial and temporal scales<ref name = "NRC1992"/><ref name = "Palmer2005"/>. Despite the large number of restorations that have taken place at a combined cost of >$1 billion per year in the United States<ref name= "Bernhardt2005"/>, effects of stream restorations are poorly documented because of extremely limited post-restoration monitoring<ref>Bilby, R.E. and Ward, J.W., 1991. Characteristics and function of large woody debris in streams draining old-growth, clear-cut, and second-growth forests in southwestern Washington. Canadian Journal of Fisheries and Aquatic Sciences, 48(12), pp.2499-2508. [https://doi.org/10.1139/f91-291 doi: 10.1139/f91-291]</ref><ref name= "Roni2008"/><ref name= "Bernhardt2011/>). It is estimated that only 10% of stream restorations are monitored or assessed after implementation<ref name= "Bernhardt2005"/>. In an analysis of 345 stream restoration studies<ref name= "Roni2008"/> found that conclusions on the effectiveness of restoration could not be drawn because of limited data on physical, chemical, and biological criteria collected primarily over short post-restoration time periods. For example, studies suggest that in-stream habitat modification can improve salmonid fish habitat and abundance, although the lack of statistically rigorous design, and high variability in responses with different in-stream restoration structures and different species make broad conclusions about efficacy difficult<ref name= "Roni2008"/>. It is not possible for many restoration studies to include monitoring in their projects due to funding limitations<ref name= "Sudduth2007"/>, but it is suggested those that can should adopt standard monitoring methods incorporating both stream structure and function responses, with measurements collected over long periods of time and across a wide range of environmental conditions (e.g., flood and drought years)<ref name = "Palmer2005"/><ref name= "Bernhardt2005"/><ref name = "Wohl2005>Wohl, E., Angermeier, P.L., Bledsoe, B., Kondolf, G.M., MacDonnell, L., Merritt, D.M., Palmer, M.A., Poff, N.L. and Tarboton, D., 2005. River restoration. Water Resources Research, 41(10). [https://doi.org/10.1029/2005WR003985 doi: 10.1029/2005WR003985]</ref><ref>Lake, P.S., Bond, N. and Reich, P., 2007. Linking ecological theory with stream restoration. Freshwater Biology, 52(4), pp.597-615. [https://doi.org/10.1111/j.1365-2427.2006.01709.x doi: 10.1111/j.1365-2427.2006.01709.x]</ref>). Furthermore, measured environmental responses should be compared to multiple reference sites (minimally impacted systems of a similar stream order and in the same ecoregion as the restored site) in order to fully assess restoration efficacy<ref name = "Palmer2005"/>.
 +
 +
==Stream restoration techniques==
 +
By their very nature, streams and rivers are dynamic ecosystems; thus, restoration efforts should focus on strategies designed to integrate dynamic physicochemical and biological processes<ref name = "NRC1992"/><ref name = "Palmer2005"/><ref name = "Thompson2005">Thompson, D.M., 2005. The history of the use and effectiveness of instream structures in the United States. Humans as Geologic Agents, 16, p.35. [https://doi.org/10.1130/2005.4016(04) doi: /10.1130/2005.4016(04)]</ref><ref name = "Wohl2005/><ref name= "Bernhardt2011/>). For example, restoration objectives focused on re-establishing a dynamic stream ecosystem may include restoring natural sediment dynamics and water flow, restoring natural riparian plant communities, and restoring natural channel configurations<ref name = "NRC1992"/>.
 +
 +
When selecting a target site for restoration, it is suggested that watershed assessments be conducted to determine appropriate locations. In practice, however, target sites are most often selected because land is available for restoration<ref name= "Sudduth2007"/>. It is important to note that if one restoration technique is conducted in multiple locations, the response of a system to restoration may not be the same because of site- and region-specific differences in geology, land use, climate, and biogeographic history<ref name = "Palmer2005"/><ref name = "Wohl2005/>. For example, an analysis of 24 restoration projects found that stream restorations were more successful in improving stream macroinvertebrate communities when the restorations were conducted closer to intact forests, which provided a source of invertebrates to recolonize restored sites<ref>Sundermann, A., Stoll, S. and Haase, P., 2011. River restoration success depends on the species pool of the immediate surroundings. Ecological Applications, 21(6), pp.1962-1971. [https://doi.org/10.1890/10-0607.1 doi: 10.1890/10-0607.1]</ref>.
 +
 +
{| class="wikitable" style="float:right; margin-left: 20px;"
 +
|+ Table 1. Categories of Stream Restoration (NRC 1992)
 +
|-
 +
| Bank stabilization
 +
|-
 +
| Channel modification
 +
|-
 +
| Fish reintroduction
 +
|-
 +
| Flow augmentation
 +
|-
 +
| Organic matter addition
 +
|-
 +
| Revegetation of banks and riparian zones
 +
|-
 +
| Land use regulation
 +
|-
 +
| Soil stabilization
 +
|-
 +
| Water quality improvements
 +
|-
 +
| Water temperature alteration
 +
|}
 +
 +
There are many types of stream restoration techniques that have been applied, and the type of restoration(s) can depend on the size and extent of the stressor, predominant land use in the watershed, position of the stream within the watershed, and the goals and objectives of the stakeholders<ref name = "NRC1992"/><ref name= "Bernhardt2005"/><ref name = "Palmer2005"/>.  Stream restoration goals and techniques are too numerous to discuss succinctly here (see Table 1). As one example, the five most common restoration techniques to improve habitat for salmonid fishes include habitat reconnection, road improvement, riparian management, in-stream habitat improvement, and nutrient enrichment<ref name= "Roni2002"/>.
 +
 +
One common restoration technique is the addition of coarse woody debris (CWD) to stream channels. CWD additions are a low-cost method to improve in-stream habitat<ref name= "Bernhardt2005"/>. In practice, nearby riparian trees are felled, cut, and staked in place within the stream channel. CWD additions can exert several positive effects on stream ecosystems including altering morphology and hydraulics of stream channels, creating habitat for benthic macroinvertebrates and fish, providing colonization surfaces for algae and other microorganisms, and increasing retention of sediment and organic matter, the latter of which is an important basal resource for many stream organisms<ref>Bilby, R.E. and Likens, G.E., 1980. Importance of organic debris dams in the structure and function of stream ecosystems. Ecology, 61(5), pp.1107-1113. [https://doi.org/10.2307/1936830 doi: 10.2307/1936830]</ref><ref>Smock, L.A., Metzler, G.M. and Gladden, J.E., 1989. Role of debris dams in the structure and functioning of low‐gradient headwater streams. Ecology, 70(3), pp.764-775. [https://doi.org/10.2307/1940226 doi: 10.2307/1940226]</ref><ref>Bilby, R.E. and Ward, J.W., 1991. Characteristics and function of large woody debris in streams draining old-growth, clear-cut, and second-growth forests in southwestern Washington. Canadian Journal of Fisheries and Aquatic Sciences, 48(12), pp.2499-2508. [https://doi.org/10.1139/f91-291 doi: 10.1139/f91-291]</ref><ref name= "Roberts2007">Roberts, B.J., Mulholland, P.J. and Houser, J.N., 2007. Effects of upland disturbance and instream restoration on hydrodynamics and ammonium uptake in headwater streams. Journal of the North American Benthological Society, 26(1), pp.38-53. [https://doi.org/10.1899/0887-3593(2007)26[38:EOUDAI]2.0.CO;2 doi:10.1899/0887-3593(2007)26[38:EOUDAI]2.0.CO;2]</ref><ref>Roni, P., Beechie, T., Pess, G. and Hanson, K., 2014. Wood placement in river restoration: fact, fiction, and future direction. Canadian Journal of Fisheries and Aquatic Sciences, 72(3), pp.466-478. [https://doi.org/10.1139/cjfas-2014-0344 doi: 10.1139/cjfas-2014-0344]</ref>. Therefore, CWD additions have been used to improve in-stream habitat for aquatic organisms, primarily fish<ref name= "Roni2002"/>, and also, have been identified as a strategy to improve in-stream nitrogen retention<ref name= "Roberts2007"/><ref name= "Craig2008"/>. However, a lack of comprehensive monitoring data has limited the ability to thoroughly evaluate the efficacy of this technique<ref name = "Thompson2005"/>. For example, Roni et al. (2002)<ref name= "Roni2002"/> found that 41% of in-stream habitat improvement studies in the Pacific Northwest increased juvenile salmonid abundance; however, only about 20% of these studies quantified responses for >5 y, and responses varied across the restoration techniques examined<ref name= "Roni2002"/>.
  
  

Revision as of 20:01, 7 October 2019

Stream restoration is often performed to reduce the effects of stressors on the environment and return stream structure and function to pre-disturbance conditions. Often, restoration projects aim to improve water quality and in-stream habitat, manage riparian zones, stabilize stream banks, and allow fish to pass barriers. Stream restorations are commonly carried out across the United States, although very few studies have assessed and monitored the long-term effects of restoration; thus, the outcomes of stream restorations are generally not well documented. Of the many possible stream restoration approaches, one prominent approach in low-gradient, sandy-bottomed streams is the addition of coarse woody debris (CWD) to improve in-stream habitat. In an experimental study summarized here, debris dams were added to 4 streams at Fort Benning Military Installation, Georgia, to mitigate the impacts of military training activities. Results were compared to 4 control streams that were not restored. There were some short-term (< 3 y) changes to stream ecosystem structure and function, but thus far, minimal long-term (~14 y) effects on these streams have been evident.

Related Article(s):


CONTRIBUTOR(S): Dr. Natalie Griffiths, Dan Isenberg, Sam Bickley, Dr. Brian Helms, and Dr. Jack Feminella

Key Resource(s):

Stream Restoration: Definitions and Scope

Stream restoration is an overarching term used to describe the process of returning stream structure and function to pre-disturbance conditions[3]. This definition of “restoration” differs from “reclamation” and “rehabilitation” in that the latter two terms describe altering a system to meet various human needs[3]. Stream restorations often focus on improving the ecological condition within the stream itself, but it is important to recognize that streams are part of larger watersheds, with both upstream-downstream and lateral connections (i.e., to riparian zones and floodplains[3]. Therefore, small-scale, in-stream restorations may have little impact if larger-scale impacts (e.g., land disturbances) are not addressed[3][5] Craig, L.S., Palmer, M.A., Richardson, D.C., Filoso, S., Bernhardt, E.S., Bledsoe, B.P., Doyle, M.W., Groffman, P.M., Hassett, B.A., Kaushal, S.S. and Mayer, P.M., 2008. Stream restoration strategies for reducing river nitrogen loads. Frontiers in Ecology and the Environment, 6(10), pp.529-538. doi: 10.1890/070080</ref>[4][6]. Instead, watershed-scale approaches focusing on improving land management practices within the watershed and also applying multiple, complementary stream and riparian restoration approaches have been recommended[3][7]Cite error: Closing </ref> missing for <ref> tag presented a hierarchical approach for restoration, with this approach specifically developed for improving fish habitat in forests and rangelands. They suggested that managers prioritize protecting intact (i.e., non-degraded) stream reaches that have high-quality habitat for fishes. Subsequent efforts should then focus on reconnecting high-quality habitats that have been disconnected hydrologically, followed by restoring ecosystem processes (e.g., restoring riparian processes by livestock exclusion), and lastly focusing on improving in-stream habitat through habitat augmentation practices (e.g., large wood or boulder additions).

Stressors to stream ecosystems that motivate restoration

Headwater streams are important components of river networks and, like most waterways, they are also vulnerable to degradation from anthropogenic and natural sources[8]. Because of their close hydrologic connection to the surrounding terrestrial environment, headwater streams can be particularly influenced by land disturbances[9][10][11]. Further, the hydrologic connectivity of river networks means that disturbances in headwaters can influence downstream ecosystems[12]. Thus, minimizing human impacts in headwater streams is important not only for protecting these ecosystems and their biodiversity but also because of the multiple services they provide to downstream ecosystems (e.g., water for drinking, bathing, recreation, consumption of fish, etc.).

A survey of stream restorations in the southeastern US revealed that environmental degradation, mitigation, and public safety were the main factors motivating stream restorations[13]. Environmental stressors include changes in land use (e.g., forestland conversion) and hydrology (e.g., water withdrawals) in the surrounding watershed[14][6]. These factors, in turn, can reduce water quality, alter water quantity, degrade in-stream habitat and associated aquatic biodiversity, and alter availability and quality of food resources for biota (e.g., organic matter inputs[3]). Therefore, the five most common goals of stream restoration projects are:

  • improve water quality;
  • manage riparian zones;
  • improve in-stream habitat;
  • allow for fish passage and
  • stabilize stream banks[1]

Restoration goals and assessment of efficacy: the importance of monitoring

Identification of a restoration project’s mission, goals, and objectives is necessary in order to evaluate the ecological success of that restoration[3][7]. Central to this approach is the implementation of pre-restoration and post-restoration monitoring at appropriate spatial and temporal scales[3][7]. Despite the large number of restorations that have taken place at a combined cost of >$1 billion per year in the United States[1], effects of stream restorations are poorly documented because of extremely limited post-restoration monitoring[15][4][6]). It is estimated that only 10% of stream restorations are monitored or assessed after implementation[1]. In an analysis of 345 stream restoration studies[4] found that conclusions on the effectiveness of restoration could not be drawn because of limited data on physical, chemical, and biological criteria collected primarily over short post-restoration time periods. For example, studies suggest that in-stream habitat modification can improve salmonid fish habitat and abundance, although the lack of statistically rigorous design, and high variability in responses with different in-stream restoration structures and different species make broad conclusions about efficacy difficult[4]. It is not possible for many restoration studies to include monitoring in their projects due to funding limitations[13], but it is suggested those that can should adopt standard monitoring methods incorporating both stream structure and function responses, with measurements collected over long periods of time and across a wide range of environmental conditions (e.g., flood and drought years)[7][1][16][17]). Furthermore, measured environmental responses should be compared to multiple reference sites (minimally impacted systems of a similar stream order and in the same ecoregion as the restored site) in order to fully assess restoration efficacy[7].

Stream restoration techniques

By their very nature, streams and rivers are dynamic ecosystems; thus, restoration efforts should focus on strategies designed to integrate dynamic physicochemical and biological processes[3][7][18][16][6]). For example, restoration objectives focused on re-establishing a dynamic stream ecosystem may include restoring natural sediment dynamics and water flow, restoring natural riparian plant communities, and restoring natural channel configurations[3].

When selecting a target site for restoration, it is suggested that watershed assessments be conducted to determine appropriate locations. In practice, however, target sites are most often selected because land is available for restoration[13]. It is important to note that if one restoration technique is conducted in multiple locations, the response of a system to restoration may not be the same because of site- and region-specific differences in geology, land use, climate, and biogeographic history[7][16]. For example, an analysis of 24 restoration projects found that stream restorations were more successful in improving stream macroinvertebrate communities when the restorations were conducted closer to intact forests, which provided a source of invertebrates to recolonize restored sites[19].

Table 1. Categories of Stream Restoration (NRC 1992)
Bank stabilization
Channel modification
Fish reintroduction
Flow augmentation
Organic matter addition
Revegetation of banks and riparian zones
Land use regulation
Soil stabilization
Water quality improvements
Water temperature alteration

There are many types of stream restoration techniques that have been applied, and the type of restoration(s) can depend on the size and extent of the stressor, predominant land use in the watershed, position of the stream within the watershed, and the goals and objectives of the stakeholders[3][1][7]. Stream restoration goals and techniques are too numerous to discuss succinctly here (see Table 1). As one example, the five most common restoration techniques to improve habitat for salmonid fishes include habitat reconnection, road improvement, riparian management, in-stream habitat improvement, and nutrient enrichment[20].

One common restoration technique is the addition of coarse woody debris (CWD) to stream channels. CWD additions are a low-cost method to improve in-stream habitat[1]. In practice, nearby riparian trees are felled, cut, and staked in place within the stream channel. CWD additions can exert several positive effects on stream ecosystems including altering morphology and hydraulics of stream channels, creating habitat for benthic macroinvertebrates and fish, providing colonization surfaces for algae and other microorganisms, and increasing retention of sediment and organic matter, the latter of which is an important basal resource for many stream organisms[21][22][23][24][25]. Therefore, CWD additions have been used to improve in-stream habitat for aquatic organisms, primarily fish[20], and also, have been identified as a strategy to improve in-stream nitrogen retention[24][5]. However, a lack of comprehensive monitoring data has limited the ability to thoroughly evaluate the efficacy of this technique[18]. For example, Roni et al. (2002)[20] found that 41% of in-stream habitat improvement studies in the Pacific Northwest increased juvenile salmonid abundance; however, only about 20% of these studies quantified responses for >5 y, and responses varied across the restoration techniques examined[20].


References

  1. ^ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Bernhardt, E.S., Palmer, M.A., Allan, J.D., Alexander, G., Barnas, K., Brooks, S., Carr, J., Clayton, S., Dahm, C., Follstad-Shah, J. and Galat, D., 2005. Synthesizing US river restoration efforts. Science. Vol. 308, Issue 5722, pp. 636-637. doi: 10.1126/science.1109769
  2. ^ Mulholland, P.J., Feminella, J.W., Lockaby, B.G. and Hollon, G.L., 2007. Riparian Ecosystem Management at Military Installations: Determination of Impacts and Evaluation of Restoration and Enhancement Strategies. Final Technical Report SI-1186. Pp.161. Report.pdf
  3. ^ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 National Research Council, 1992. Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy. National Academies Press. doi: 10.17226/1807
  4. ^ 4.0 4.1 4.2 4.3 4.4 Roni, P., Hanson, K. and Beechie, T., 2008. Global review of the physical and biological effectiveness of stream habitat rehabilitation techniques. North American Journal of Fisheries Management, 28(3), pp.856-890. doi: 10.1577/M06-169.1
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See Also