by Darrel Drake, Brenda Tozer, and Geoffrey Stillwell
Semester Project for ES-767, Wetland Environments,
Earth Science Department, Emporia State University (2012)
Quantitative Status of the PPR (Prairie Pothole Region)
Historic Anthropomorphic Impacts
Opportunities for Conservation and Restoration
Government Conservation and Management Programs
Future of Wetlands in the PPR
Appendix A-USFWS and Other Government Programs for Preserving Wetlands in the PPR
Appendix B-Definition of Restoration Terminology
The landscape holds a high number of potholes that are accumulatively effective in retaining snowmelt water that would otherwise create flood conditions, see Figure 2.
|The number of potholes have been greatly reduced due to drainage of the potholes in order to further agriculture.|
The PPR is the most productive wetland waterfowl habitat in North America.
|The glaciers that formed the pothole region occurred mainly during the Pleistocene Epoch, Figure 5. The last glaciers retreated about 14,000 to 12,000 years ago. The landscape is relatively young and experiences moderate rainfall. Therefore, most prairie potholes are not connected to overland flow. Most prairie potholes resulted from the melting of blocks of buried glacial ice that melted away to leave depressions. The potholes range from a relatively small area of <0.4ha to as large as 16.2ha, hence the name potholes. Basins that occur larger than 16.2ha are considered lakes. The major water supply for potholes is snow melt water that runs over frozen ground during the Spring Season. Most potholes are less than 25 feet deep, with few deeper than 5 feet. The shapes of the potholes are usually irregular due to the glacial processes that produced it. The outline of the pothole after its origin is affected by erosion and deposition of materials. As a result from erosion and weathering procecesses on the glacially derived shape, most potholes are saucer shaped. Prairie potholes are isolated systems with limited interconnections (Eldridge, 1990).|
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The PPR experiences extreme weather. The PPR is influenced by three large air masses, continental polar, maritime polar and maritime tropical, Figure 7. The interaction of these three air masses creates one of the most extreme and dynamic climates on Earth. The southern PPR is wetter and warmer than the northern PPR. Temperatures range from -40 °C to above 40 °C in winter and summer respectively. Isolated summer thunderstorms can inundate an area with several centimeters of water while surrounding areas remain dry. Winds up to 60 km/hr. can dry wetlands. Temperatures can dramatically reduce the number of wetlands. Precipitation can triple from the west to the east, from 300 mm/yr to 900 mm/yr,see Figure 6.The mean average temperature range is from 1 °C in north to 10 °C in the south. The large geography of the region elicits differences in climatic patterns for local areas. The south-eastern section is cooler and receives more rainfall in summer months than the semiarid western section (USDI, 2006).
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|Landscape variations induced through glacial activity has influenced hydrology with the creation of subregions, Figure 8. The Missouri Coteau, which runs parallel and east to the Missouri River, from Montana to Nebraska, is a hummocky region. The Coteau is an area where the ponds and sloughs are not connected to each other and streams do not flow through this area. The PPR lies upon a layer of unconsolidated glacial till that ranges from tens to hundreds of meters thick. The unconsolidated portions are an anisotropic environment with a mixture of fine silts, clays, sand, and rocks. Lenses are another obstacle. The conduits in the glacial till are not uniform. The layerings of the formations are closely related to a flaking crust in which conduits can be interconnected or blocked. Some conduits travel a long distance before outflow to the surface. Formations of thick clays and silt form aquitards that isolate different aquifers. Sand and rocky areas that occur as extensive sheets provide the larger portion of recharge to the aquifers as potholes have a minor role with groundwater supply (LaBaugh, 1998, van der Kamp and Hayashi, 1998).|
Pothole hydrology is varied by the soil as well as the presence of water. A prominence of silt, sand, or clays will influence the hydraulic conductivity and subsequent seepage that would occur. Potholes normally contain montmorillinitic soils that are smectite clays. The absorbance capacity of the clays allows the basins to acquire a commensurate amount of water and then the soils swell to slow seepage (Sloan, 1972).
Wetlands are classed into four classes based on water permanence as:
Class I: ephemeral, Class II & III: temporary/seasonal, Class IV: semi-permanent, and Class V: permanent. Ephemeral are dry by the end of Spring when the last frost occurs. Temporary/seasonal wetlands fill and dry annually and are distinguished by seasonal wetlands having a larger area. Semi-permanent wetlands contain water continuously for years then dry out. Permanent wetlands have a water level over decades. Permanent and semi-permanent wetlands normally receive groundwater. (Stewart and Kantrud, 1972).
When the groundwater table is close to the surface and an interface is created a basin may receive from or expel to the aquifer depending upon the gradient or elevation of the basin as illustrated in Figure 9. Basins with a boundary below the water table and a gradient toward the water table are flow through wetlands. Basins with higher topographic elevations or a gradient that dips toward the water table will recharge the aquifer. Basins below the water table receive groundwater inflow (LaBaugh, 1998).
Water loss occurs by means of evapotranspiration, seepage, and outflow to groundwater. Few potholes experience spill over as is the reason for the lack of interconnected pathways. Evapotranspiration takes the largest portion of water as it is a direct process. Seepage occurs with basins that are not connected to the water table. The water slowly seeps out from the basin boundaries and saturates the surrounding ground. The wet meadow vegetation then transpires the water to the atmosphere. Outflow to ground water occurs when a basin interfaced with the aquifer has a higher elevation than or dips toward the water table (Stewart and Kantrud, 1972, LaBaugh, 1998).
Pothole salinity ranges from fresh water to a level of salinity several times greater than that of sea water.Water quality is influenced from both water loss processes and groundwater transmission. The ground water passes through glacial till that was ground from the sedimentary bedrock that contained pyrite and calcium carbonates (van der Kamp and Hayashi, 1998). The minerals have leached into the groundwater as sulfate and carbonate salts. When groundwater flows into a basin the salts are introduced to the hydrology of the wetland. Water loss processes such as seepage and ground water outflow reduce the salinity of the water pool. Salinity is highest in basins that receive groundwater inflow from all boundaries because evapotranspiration is the only water loss avenue which leaves salts as an evaporite. Indicators for the salinity levels in a given basin are reflected in the vegetation that thrives (Stewart and Kantrud, 1972).
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The 77.8 million hectare area known as the prairie pothole region (PPR) occurs in both Canada (60%) and the United States (40%). This treatment focuses on the U.S. PPR. From the 1870s to the 1970s fifty percent of wetlands were drained in the PPR (NRC, 1992). The PPR occurs within five states with wetland losses ranging from twenty seven to eighty nine percent (Johnson et al., 1994), with ten percent remaining in a semblance of pre settlement condition (Mitsch et al., 2007). This region is sometimes referred to as the northern prairies and plains. The PPR is also considered amongst the most productive agricultural regions of the world, producing 33% of the grain and soybean production of the U.S. (NRCS, 2011).
|The agricultural benefit is gained at the expense of both drained wetlands and alteration of the hydrology of the region. Drainage ditches and drainage tiles were installed to “reclaim” the land for agricultural suitability (NRC, 1992). Waterfowl is frequently used as an indicator of biological integrity and productivity. Fifty percent of the continental waterfowl and grassland bird species/population is thought to nest in the PPR (Johnson et al., 1994). The wetlands that provide the biological productivity are in tension with the altered human landscape that provides agricultural productivity. Ninety six percent of the U.S. prairie pothole region is privately owned (Johnson et al., 1994). Most potholes are small (<1ha), may have a density of 40/km2, are seasonal/temporary, and may have constituted greater than 20% of the pre settlement PPR region (Gleason et al. 2009).|
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The U.S. PPR is mostly contained in tall, mixed, and short grass prairies. In most grassland areas soil, sediment erosion, and nutrient loss exceeds replenishment as soil loss may occur at three times the rate of formation. Climate and fire are major processes that determine the structure of grassland communities. Prairie vegetation was adapted to seasonal fires and this is an adaptive advantage that native grasses have over woody plant species in pre settlement times. Grazing by bison was also a major pre settlement adaptive pressure on grassland communities (Mac et al., 1998).
In the northern prairies cattle have replaced bison. Native grasslands are now isolated islands surrounded by landscape scale agriculture. Many Eurasian plant species act as invasive vectors on the native plant community. Wildfires, essential to shaping natural grassland and wetland communities and controlling woody species, are now essentially absent. Woody plants and cattails, once rare in the northern prairies, are common. Hydrology was also altered, as many wetlands were drained. Soil drainage was accomplished through the installation of drainage tiles and drainage ditches. The scale of soil drainage alteration is consistent with the scale of agriculture. By about 1900 both grey wolves and grizzly bears were extirpated. The elimination of wolves has ecologically released the population of smaller predators such as fox, coyote, and raccoon. An unfortunate consequence of this faunal composition change is that smaller predators are effective at preying on ground nesting birds (Johnson et al., 1994).
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PPR wetlands are often referred to as “amongst the most productive ecosystems, …, ranking with tropical rainforests” (Eldridge, 1990). This statement refers to primary productivity under optimum hydrological conditions during the growing season. An exact quantification of this claim is difficult to find, and Eldridge’s claim is based on a 1980s figure that compares all freshwater wetlands to rainforests: i.e. not specifically prairie potholes. If the northern prairies are seen as an intensely managed landscape, then the islands of diversity within the landscape (potholes) should be seen as important beyond their primary productivity. This is apparent in the importance of the PPR to waterfowl populations in North America.
Given the impacts mentioned above, there may seem to be little chance of maintaining this ecosystem. Such a conclusion may be overly pessimistic. The PPR wetland ecosystems are adapted to cycles of extreme disturbance. Johnson et al. (1994) states the status of the PPR succinctly as “Plant communities of the region, especially those in wetlands, have always been unstable. Cyclic weather patterns, grazing by huge herds of bison and other ungulates, and fires were integral to the landscape, …, It is impossible to return to the landscape that was present in pre-settlement times. Some species have been extirpated, certain habitats eliminated, and wetland hydrology irreversibly altered. The Prairie Pothole Region, although sparsely populated, is one of the most intensively managed landscapes in North America. It will remain so despite talk of the Buffalo Commons. These wetlands evolved and thrive in an environment of constant extreme disturbance. Perhaps what is often described as an ecosystem (PPR wetland) is really a suite of opportunistic plant communities responding to cycles of extreme cycles of climate, fire, and herbivory. The simple conservation mindset is that these wetlands will restore themselves through their seedbank and natural growth processes when their hydrology is restored. If this is true, then prospects for wetland restoration would seem rather optimistic.
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Ninety five percent private ownership of lands in the PPR dominates the political, social, and economic context for government management of those lands. Purchasing the cooperation of landowners may avoid some political and social issues that government land purchases cause (removing land from property tax rolls or removing families from property). The federal government may enter into contractual and various other agreements with landowners to enhance or restore wetlands. With their mission or protecting and preserving migratory waterfowl populations, the USFWS is particularly active in managing various government programs in the PPR (see Appendix A). By 1992 approximately 9% of the PPR area was in state, private, or federal protection programs (Johnson et al., 1994).
Ten-year contracts through the CRP/WRP programs (Appendix A) are an example of a popular program administrated by federal agencies. When the owner does not renew the contract, the wetlands are removed from protected status. For example in 2007 162,000 of 1.38 million contractually protected hectares in North Dakota were taken out of the CRP program. CRP acreage is typically highly erodible land. Rising commodity prices meant farmers could make more money by raising crops on fragile soils than their contracts under the CRP program pay per contractual year (Wilson 2008). A new organization involved with structuring conservation in the PPR is the Prairie Pothole Joint Venture (PPJV). This organization was built as a cooperative effort to concentrate resources for the North American Water Fowl Management Plan (1987 signatories-U.S., Canada, and Mexico). The growth spurt of the PPJV was 1995-2005 based on USFWS planning and a partnership between federal and state agencies as well as various conservation organizations. In 2005 PPJV claimed 1.53 million hectares of restored habitat. However the PPJV anticipates a loss of 0.77 million hectares in the 2008-2012 CRP acreage withdrawal losses. There are many issues beyond the scope of this discussion that challenge the future success of the PPJV effort including; more aggressive farming and range practices that reduce habitat, social and political attitudes against government land management in PPR states, energy sector crops, and global warming (PPJV 2005). The PPJV would seem to better posed to manage conservation programs in the PPR than government agencies alone.
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In the 1990s restoration consisted of breaking drainage tiles, filling ditches and waiting for natural recovery of plant communities. While restoration was a difficult process, it was believed that potholes generally had reasonably good potential for restoration. The chief obstacle was viewed as the absence of a program or method of convincing owners to take wetlands out of agricultural production (NRC 1992). The NRC study also included an assessment of 18 pothole restoration case studies which followed the prescribed restoration steps above. Though the restorations were well planned, the restored wetlands were deemed to be of little wildlife value and low floristic diversity. The NRC concludes that these early restorations were successes with lessons learned. Though there was no monitoring or goals, potholes were removed from agricultural production, some wetland functions were restored, and these wetlands were able to support duck populations. Gleason et al. conducted a survey of 204 restored CRP and WRP PPR wetlands for the USGS in 2008. They selected cropped wetlands as the baseline (a strange choice) and native wetlands as their upper bound for floristic diversity. This survey had similar results to the NRC survey. However, they also concluded that this diversity approaches 50% of the native wetlands. They try to make the point that floristic composition is a poor choice as a measure of wetland quality, since species composition changes in response to many factors. This statement may be true for the PPR of the future, but these authors are trying to argue for a diminished standard of restoration goals in the here and now.
An outline of the wetland restoration process is described in Aber et al. 2012 (Chapter 13). From today’s perspective, the early pothole restoration may have been successful for waterfowl production, but not for the wetland ecological structure or function of pothole wetlands (see Appendix B for definitions). Suppose the waterfowl population increase rests entirely on restored wetlands in a state of ecological decline and extensive predator control is required to preserve nesting sites in poor habitat buffers. Then duck populations may be sustained only so long as extraordinary measures are funded and managed. Good ecological restoration produces self-sustaining and resilient ecosystems. Better wetlands with quality buffer habitat for ground nesting birds may be a self-sustaining resilient alternative to the current PPJV/USFWS model. However, this may be an unrealistic goal within the PPR political and land ownership context.
Perhaps restored PPR wetland communities have simply not matured. In 2000, ecological restoration was a new practice with incomplete knowledge (Young et al. 2005). However Zedler (2000) makes the case that PPR wetland seed banks are exhausted and wetland isolation does not allow a sufficient number of new plants or seeds to become established relative to invasive species after restoring hydrology. This is because native species are dispersal limited and are unlikely to reappear without seeding. Replanting may be a necessity to avoid ecological opportunity for weed species. Myla et al. (2008) conducted a 19 year floristic survey on 28 restored prairie pothole wetlands. They found that in the first 10-12 years the long term species assemblages become established. Larger, more permanent wetlands have less species boom and bust than short seasonal wetlands. After 10-12 years extinctions typically exceed colonizations in all wetlands, and there is little chance that these wetlands will become more diverse. The rationale for dispersal limits are isolation, infrequent flooding, and the dispersal advantages that invasives have over native species. As an example Kettenring (2006 in Myla et al. 2008) found invasive species constituted 77% of the seed rain in restored wetlands. These new planning practices were simply not the standard practice in the PPJV or USFWS during the period from 1985-2005 and the typical restored wetlands of today reflect these problems in floristic diversity and invasive species.
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Climate change will probably alter plant community composition within the PPR wetlands across the various guilds or zones. Maintaining and restoring the plant assemblages that are identified with potholes will inevitably be more difficult as future temperatures increase and water supply changes. Kentula (1993) advocated for more information on mature restored wetlands and better designed model restoration wetlands. Many factors in the future may render such expectations as unobtainable. Given that invasives are better at colonizing, dispersing, and limit or dominate the developing species assemblages in the marsh and wet prairie guilds (Myla et al. 2008), the climax community goal of restoration in the future may be a moving target. Despite the desire to preserve current natural communities or ecosystems, climate and land management practices may change the composition of PPR guild plant assemblages. The effects of future ecological changes on waterfowl nesting patterns in the PPR are unknown.
The northern prairies are a mixture of ranch and cropland. The predominant row crops, corn and soybeans, provide little wildlife benefit. More drought resistant strains of corn and soybeans are always being planted and researched, meaning a greater amount of sensitive lands in the CRP or WRP may be more profitable to the owner if withdrawn and put into production. The expansion of cropland consumes both rangeland and conservation lands. Less grassland/wetland will be preserved due to agriculture and greater pressure due to grazing on available rangeland. Rising commodity prices has also led to a decrease in CRP contracts, which will place more acreage into production. Wind energy and bio fuels will also impact regional land use (PPJV 2005). Many of the PPR states have seen a 10% demographic decrease in family farms in the past two decades. Agency officials must also be creative since property owners will be a necessary component of conservation and some of those owners are corporate owners. It is obvious that many species both flora and fauna have been in decline or artificially maintained at constant levels in recent decades (Mac et. al. 1998). It is also obvious that many ecosystem stressors (climate change and habitat loss) will emerge in the next few decades for which there will be fewer resources devoted to conservation to sustain wetlands. The future may even be more challenging than the present.
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Aber J. S., Aber S. W., and Pavri F., 2012. Wetland environments: A global perspective. Wiley-Blackwell. In Press.
Eldridge, J. 1990. 13.3.5. Ecology of Northern Prairie Wetlands. Waterfowl Management Handbook. Paper 17. Digital Commons at University of Nebraska, USFWS. Accessed online at http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1016&context=icwdmwfm
Gleason R.A., Euliss-Jr. N.H., Tangen B.A., Laubhan M.K., and Browne B.A. 2009. USDA Conservation Program and Practice Effects on Wetland Ecosystem Services in the Prairie Pothole Region. Ecological Applications: 21(3) Supplement 2011:S65-S81. Accessed online at http://www.esajournals.org/doi/pdf/10.1890/09-0216.1.
Gleason, R.A., Laubhan, M.K., and Euliss, N.H., Jr., eds., 2008, Ecosystem services derived from wetland conservation practices in the United States Prairie Pothole Region with an emphasis on the U.S. Department of Agriculture Conservation Reserve and Wetlands Reserve Programs: U.S. Geological Professional Paper 1745,58
Johnson D. H., Haseltine S. D., and Cowardin L. M.. 1994. Wildlife Habitat Management on the Northern Prairie Landscape. Landscape and Urban Planning 28:5-21. Bozeman, MT: Mountain Prairie Information Node. Accessed online at http://www.pdfio.com/k-568676.html#
Kentula M.(USEPA)., 1993. Restoration, Creation, and Recovery of Wetlands; Wetland Restoration. USGS. Acceessed online at http://water.usgs.gov/nwsum/WSP2425/restoration.html
Mac M.J., Opler P.A., and Puckett Haecker C.E. 1998. Status and Trends of the Nation’s Biological Resources; Grasslands. USGS. ISBN 016053285X. Accessed online via web address http://www.nwrc.usgs.gov/sandt/Grasslnd.pdf
Mitsch W. and Gosselink, J., 2007, Wetlands, John Wiley and Sons. Hoboken NJ, USA. 582p. ISBN 978-0-471-69967-5
Moore T. L. and Hunt W.F. 2011. Stormwater Wetlands and Ecosystem Services. North Carolina State University Urban Waterways Series. Accessed online at http://www.bae.ncsu.edu/stormwater/PublicationFiles/WetlandEcosystemServices2011.pdf
Myla F., Aronson J., and Galatowitsch S. 2008. Long Term Vegetation Redevelopement of Restored Prairie Pothole Wetlands. Wetlands. 28:4:883-895
NRC Committee on Restoration of Aquatic Ecosystems. 1992. Restoration of Aquatic Ecosystems; Science, Technology, and Public Policy. National Academy Press. Washington D.C. 552 P. ISBN 0-309-04534-7
NRCS. 2011. Conservation of Wetlands in Agricultural Landscapes of the United States: Summary of the CEAP Wetlands Literature Synthesis. United States Department of Agriculture. Accessed online via web address http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1041601.pdf
Prairie Pothole Joint Venture (PPJV). 2005. Complete Prairie Pothole Joint Venture Implementation Plan. USFWS & Partners. Accessed online at http://www.ppjv.org/implement2.htm
Sloan, C., 1972, Ground-Water Hydrology of Prairie Potholes in North Dakota, Hydrology of Prairie Potholes in North Dakota, Geological Survey Professional Paper, 585-C. Accessesd on line via web address: http://library.ndsu.edu/exhibits/text/potholes/585c.html
Stewart, R., and Kantrud, H., 1972, Vegetation of Prairie Potholes, North Dakota, in Relation to Quality of Water and Other Environmental Factors, Hydrology of Prairie Potholes in North Dakota, Geological Survey Professional Paper, 585-D.
U.S. Department of the Interior, 2006, U.S. Geological Survey, Wetlands of the Prairie Pothole Region: Invertebrate Species Composition, Ecology, and Management. Accessed on line at http://www.npwrc.usgs.gov/resource/wetlands/pothole/prairie.htm
U.S. Global Change Research Program (USGCRP). 2005. Great Plains Region Fact Sheet. USGCRP. Accessed online at http://www.globalchange.gov/images/cir/region-pdf/GreatPlainsFactSheet.pdf
Van der Kamp, G., and Hayashi, M., 1998, The Groundwater Recharge Function of Small Wetlands in the Semi- Arid Northern Prairies Great Plains Research: A Journal of Natural and Social Sciences, Paper 366. Accessed online at http://digitalcommons.unl.edu/greatplainsresearch/366
Wilson R. 2008. CRP R.I.P?. Prairie Pothole Joint Venture. Accessed online at http://www.ppjv.org/PPJV_presntations/CRP_RIP_June_2008.pdf
(WIW) Watersheds Information on Wetlands. 1995. Wetlands Functions (or Processes) and Values, Wetland Management, and Major Causes of Wetland Loss and Degradation. North Carolina State University. Accessed online at http://www.water.ncsu.edu/watershedss/info/wetlands/index.html
Young T.P., Petersen D.A., and Clary J.J., 2005. The Ecology of Restoration; Historical Links, Emerging Issues, and Unexplored Realms. Ecology Letters. (2005) 8: 662-673. Accessed online at http://ucce.ucdavis.edu/files/filelibrary/5733/28426.pdf
Zedler J.B. 2000. Progress in Wetland Restoration Ecology. TREE (2000) 15: 402-407. Accessed online at http://academic.udayton.edu/RyanMcEwan/Courses/EcolRest/Zedler_Reading.pdf
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Swampbuster provision of the 1985 and 1990 Farm Bills (disincentives for using wetlands)
CRP/WRP-Conservation Reserve (CRP-10 year contract) and Wetlands Reserve (WRP-Permanent easement) Programs (1985 and 1990 Farm Bills)-10 year contract
Water Bank Act-1970 (10 year easement)
Migratory Bird Hunting and Conservation Stamp Act/Small Wetland Acquisition Program (SWAP)-1934 (purchase or easement), Easements generally prohibit drainage, burning, and filling of wetlands and are enforceable. Easements may include restoration or technical assistance and are also instruments of federal and state agencies
North American Wetlands Conservation Act of 1989 (enhancement of wetland protections to North American Waterfowl Management Plan, purchase and easements)
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Structure: The spatial and temporal organization of ecological conditions. Ecological structures directly link to ecological functions, http://www.kingcounty.gov/environment/waterandland/shorelines/program-update/glossary.aspx, May also be used to mean community structure or biological organization.
Ecosystem Function-Physical, chemical, and biological processes occurring in and making up the ecosystem (WIW 1995)
Value-A subjective estimate of worth, merit, quality, or importance, may include indirect or future uses (WIW 1995)
Ecosystem Service- refers to any of the benefits that ecosystems—both natural and seminatural—provide to people (Moore et al. 2011)
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