Between the watersheds and at distances of two or three miles from one another were little clear brooks with banks of black sod, their waters flowing on floors of bright colored glacial pebbles; ... They were beautiful little brooks, so clear, so overarched with tall grasses and willows, so plaided with the colors of the pebbles in the sun, so dark and mysterious in the shade; with secret pockets under the soddy banks for the shiners, pumpkinseeds, dace, chubs, and other small fish which populated the pure waters. . . . All those beautiful brooks are now forever gone. They were such lovely streams to us children ... : but they were like delicate flowers, too tender for be touch of humanity. -Herbert Quick, 1925, recalling the Iowa prairie of the 1860s

CHAPTER 19

WATERSHED RESTORATION AND AGRICULTURAL PRACTICES IN THE MIDWEST: BEAR CREEK IN IOWA

Thomas M. Isenhart, Richard C. Schultz, and Joe P. Colletti

The Western Corn Belt Plains ecoregion, which covers most of Iowa and parts of surrounding states, can be characterized as extensive cropland on level to gently rolling, dissected glacial till plains, hilly loess plains, and morainal hills with broad smooth ridgetops (Griffith et al. 1994). This landscape has been largely converted to agricultural uses; more than 80% of most counties of the ecoregion are dedicated to corn, soybeans, and forage for livestock (Burkhart et al. 1994). Nearly two-thirds of the native hardwood forests have been converted to row crop agriculture or pasture. Modification of the local and regional hydrology has been an essential part of this land use conversion. Annual cultivation has reduced soil quality, lowering rates of infiltration and increasing surface runoff. Creation of extensive networks of subsurface tile drains, excavation of surface drainage ditches, and channelization of many perennial streams has facilitated the conversion of nearly all prairie and wetland acreage to agricultural uses and contributed to many off-site, downstream problems of water flow and quality.

This large-scale modification of regional hydrology and terrestrial and aquatic ecosystems has had profound effects on the biological integrity of the surface waters of the region. Menzel (1983) reviewed the natural structure and function of stream ecosystems of the corn belt region with special reference to the impacts of past and present agricultural management practices. He concluded that effects on water quality were not the sole problem, but that aspects of water quantity, habitat structure, and energy transfer were also often profoundly affected by agricultural land use practices. This alteration of the physical, chemical, and biological processes associated with the water resource has dramatically reduced the species composition and diversity of the aquatic ecosystems and the functional organization in the region (Karr 1991).

A challenge for resource managers in such modified landscapes is the development and implementation of restoration-based management approaches that build upon traditional soil and water conservation and pollution control efforts. One promising approach to increasing the effectiveness of efforts to protect soil and water quality while also enhancing the integrity of the terrestrial and aquatic systems is the creation or restoration of landscape buffer zones (NRC 1993b). For example, riparian vegetation, particularly the vegetation bordering smaller streams and tributaries, is now recognized as an important resource that should be protected to serve as a sink for sediments, nutrients, and pesticides, to protect the streambank from erosion, and to reduce excessive runoff into stream channels (NRC 1993b). However, most of the consider-able body of evidence confirming the ecological value and effectiveness of riparian zones as sink-s for nonpoint source pollution has come from existing vegetated riparian zones (Lowrance et al. 1984, 1985; Peterjohn and Correll 1984; Jacobs and Gilliam 1985; Cooper et al. 1987; Lowrance 1992; Osborne and Kovacic 1993; Castelle et al. 1994; Hill 1996). Little information is available for restored or constructed riparian buffer systems in extensively modified agricultural systems, particularly for buffer systems in the midwestern United- States (Osborne and Kovacic 1993).

Superimposed on the physical aspects of landscape restoration efforts are the social, political, and economic questions associated with land ownership patterns in the region. About 92% of the land in Iowa is in private ownership (Iowa Agricultural Statistics Service 1994). Although most landowners seem to agree that landscape buffers would function to improve water quality, most also indicate a need for shared private and public responsibility associated with the voluntary establishment of such buffers (Colletti et al. 1994). Thus, for implementation to occur on a watershed scale, restoration models must remain flexible enough to fit the objectives of private landowners yet be scientifically robust enough to attain governmental and public acceptance.

This chapter describes a watershed management approach for the environmental enhancement of intensively modified agricultural landscapes in the Midwest. An explicit goal of the project described is to develop a riparian management system that has broad-scale applicability to watersheds in the Midwestern agroecosystem. This is being accomplished by designing a management system with several components, each of which can be modified to fit local landscape conditions and landowner objectives. Specific objectives of these components are to intercept eroding soil and agricultural chemicals from adjacent crop fields, slow flood waters, stabilize streambanks, and provide wildlife habitat and alternative, marketable products. Additionally, such management systems may improve local aquatic systems by restoring ecological functions associated with the riparian zone. This ecological restoration may be brought about by reducing discharge extremes to modify the flow regime, improving structural habitat, and restoring energy relationships by adding organic matter and reducing temperature and dissolved oxygen extremes.

DESCRIPTION OF THE BEAR CREEK WATERSHED

The Bear Creek watershed in central Iowa is a small (26.8 square miles) drainage basin, typical of the region in terms of landscape and land use. The watershed is located within the Des Moines Lobe subregion of the Western Corn Belt Plains ecoregion, one of the youngest and flattest ecological subregions in Iowa (Griffith et al. 1994). In general, the land is level to gently rolling and has a poorly developed stream network. This region was once part of the vast tallgrass prairie ecosystem, which was interspersed with wet prairie marshes in topographic lows and gallery forests along larger streams and rivers. Soils of the region were primarily developed from glacial till and alluvial, lacustrine, and -wind-blown deposits. Present land use in the Bear Creek watershed is typical of the region: over 87% of the land area is devoted to row crop and pasture agriculture.

The presettlement landscape and drainage history of the Bear Creek watershed is being described using original land survey notes (approximately 1847) and accompanying field plat maps (K. Anderson, Iowa State University, unpublished data). Early county atlases, original drainage district maps, and historical accounts by early settlers provide a historical perspective of the dramatic changes in watershed hydrology and the modification of the prairie, wetland, and riparian ecosystems that have occurred since European settlement of the region. The townships through which Bear Creek flows were originally surveyed in 1847. These surveys suggest that prior to settlement, the watershed was "rolling prairie" with "first rate soil" and a substantial portion was "low and marshy." Native forest was limited to the Skunk River corridor into which Bear Creek flowed. The upper portion of the watershed was characterized as low, wet prairie connecting more defined marshes and would likely have contained intermittent or seasonal water flow.

Subsequent changes have dramatically altered watershed hydrology and have resulted in the change of the upper watershed from a low, wet prairie landscape with slowly moving water to one with a well-defined perennial stream and numerous tributaries. Conversion of the land from native vegetation to row crops, extensive subsurface drainage tile installation, and ditch dredging have resulted in substantial stream channel development and incision. Records suggest that artificial drainage of marshes and wet prairies in the upper reaches of the Bear Creek watershed was completed by about 1902, with ditch dredging completed shortly thereafter. While the main stream system appears to have remained about the same since that time, significant channelization continued into the 1970s. Modern stream systems also indicate development of intermittent .flow drainages throughout the watershed. Ground surveys show that these are typically grass waterways associated with agricultural row crops.

Such dramatic changes in regional hydrology and vegetation have had substantial impacts on water quality and the biotic integrity of terrestrial and aquatic ecosystems. The alteration of headwater fish communities in the Midwestern states after agricultural development has been well documented (Menzel et al. 1984; Karr et al. 1985). Numerous fish species adapted to conditions of clear water, firm substrates, and lush aquatic-vegetation have been widely decimated and replaced -by ecological generalist species (organisms having broad environmental tolerance ranges and relatively unspecific resource requirements) that are tolerant of degraded habitat conditions, such as turbid, warmer waters, and that have wide functional flexibility (the ability to use a wide range of resources), especially for food and reproductive requirements (Menzel et al. 1984; Liang 1995). Collections of the fish community made in Bear Creek from 1991 to 1993 (Liang 1995) demonstrate this shift to be the case in this watershed. Fish populations are dominated by minnows (Cyprinidae), with 11 species represented. Three sucker species (Catostomidae), three bullhead catfish species (Ictaluridae), and three sunfish species (Centrarchidae) were also collected, though in much fewer numbers than the minnows. The johnny darter was well represented. As a group, the dominant species found in Bear Creek may be characterized as ecological generalists. Many of the dominant species are omnivores that feed on invertebrates, algae, and organic detritus. They also commonly have an extended reproductive period and are able to use various substrates and structures for reproduction (Liang 1995).

Similarly, invertebrate community structure of Iowa headwater streams modified by agriculture demonstrates a relatively low diversity, dominated by functional groups (groups composed of different species that perform a similar ecological function within an ecosystem) adapted to collect a wide range of organic matter or to scrape algae attached to rocks or other substrates (Barnum 1984; Menzel et al. 1984). Invertebrate density and biomes (the summed mass of individuals in a given volume or area) can be relatively high in these streams, particularly within those groups adapted for using the predominant food resource, fine particulate organic matter (Barnum 1984). These communities must also be adapted to the wide swings in temperature and dissolved oxygen characteristic of these stream systems.

Land ownership in the Bear Creek watershed is typical of the region; nearly all of the land is privately owned. Public lands are limited to road rights-of-way and parcels owned within the small community of Roland.

RESTORATION APPROACH

Restoration efforts in the Bear Creek watershed were begun in 1990 by the Agroecology Issue Team of the Leopold Center for Sustainable Agriculture and the Iowa State University Agroforestry Research Team. Other stakeholders in this effort have included the local farmer-owned cooperative, Iowa Department of Natural Resources, U.S. Department of Agriculture, U.S. Environmental Protection Agency, and Pheasants Forever.

A first step in the project was to conduct a watershed-scale assessment of land use, condition of the riparian zones, and stream and ground-water quality. This information was combined with geographic information system data and computer modeling to develop vulnerability maps for the watershed to identify critical stream reaches where modified management might be expected to reduce the impact of nonpoint source pollution on Bear Creek. A survey of watershed residents and landowners was also conducted at the initiation of the project to determine the level of concern for water quality problems, identify acceptance of a riparian management system, and quantify the value placed on improvement of surface and groundwater quality (Colletti et al. 1994). Survey respondents indicated a concern for nonpoint source pollutants and a desire to improve water quality in Bear Creek. Insights gained from survey results are combined with research relating to the effectiveness of riparian systems to guide watershed-level planning for soil conservation and water quality improvement.

The second stage of the work has been the actual development and establishment of the riparian management system model along stretches of Bear Creek and evaluation of the model systemâs effectiveness in reducing nonpoint source pollution. The riparian management system consists of three major components (1) constructed, multispecies riparian buffer strip, (2) soil bioengineering technologies for streambank stabilization, and (3) constructed wetlands to intercept and process nonpoint source pollutants in agricultural drainage-tile water. In addition, rotational grazing systems that limit livestock access to the creek channel are being, demonstrated. Restoration efforts to date include collaborative studies and demonstrations in the upper half of the watershed. This work was initiated along a 0.6-mile length of Bear Creek on the Ron and Sandy Risdal farm. Subsequently, a buffer strip system has been planted along an additional 1.8 miles of Bear Creek on three farms upstream from the original site.

Multispecies Riparian Buffer Strip

The general multispecies riparian buffer strip layout consists of three zones (Figures 19.2, 19.3). Starting at the creek or streambank edge, the first zone is a 33-foot-wide strip of four to five rows of trees, the second zone is a 12-foot-wide strip of one to two rows of shrubs, and the third zone is a 21-foot-wide strip of native, warm-season grass. Fast-growing native trees, such as willow, poplar, silver maple, and green ash, are planted nearest the stream to provide a functioning multispecies riparian buffer strip in the shortest possible time. Where site conditions permit, slower-growing species, such as northern red oak-, bur Oak, swamp white oak, or black walnut can be planted in the outer rows. The trees provide perennial root systems for streambank stabilization and long-term nutrient storage close to the stream.

FIGURE 19.1.-The riparian management system model integrates a multispecies buffer strip, streambank stabilization technologies (soil bioengineering system), and constructed wetlands.

Shrubs are included in the design because they have permanent roots and because they add habitat diversity. Their multiple stems also function to slow flood flows. The mixture of species used includes ninebark, redosier, and gray dogwood, common chokecherry, Nanking cherry, hazel, and nannyberry. Other shrub species can be used, especially if they are native and provide the desired , wildlife habitat and aesthetic characteristics.

The grass zone functions to intercept and dissipate the energy of surface runoff, trap sediment and agricultural chemicals in the surface runoff, and provide a source of organic matter for soil microbes that can metabolize nonpoint source pollutants. A minimum width of 20 feet of switchgrass is recommended because it produces a uniform cover and has dense, stiff stems that provide a highly frictional surface to intercept surface runoff and facilitate infiltration. Other warm-season grasses, such as big bluestem and Indiangrass, and native forbs may also be included within the mix. Because of its growth habit, switchgrass should be used where surface runoff is most severe (Dabney et al. 1993).

The multispecies riparian buffer strip model presented here prescribes a zone of trees, shrubs, and prairie grass that, in total, is 66 feet. Although these species combinations and width provide a very effective buffer system, they are not the only combinations that can be effective. Site conditions (e.g., soils and slope), desired buffer strip biological and physical function(s), landowner objectives, and cost-share program requirements should be considered in specifying speciescombinations and placement. At a minimum, a native grass community with a width of 20 to 30 feet is needed to meet the objectives of a basic, functioning system.

 

FIGURE 19.2.-The multispecies riparian buffer strip model includes tree rows closest to the stream, next to the trees, shrubs, and then a strip of switchgrass adjacent to the cropland.

Monitoring and ongoing research- One of the best ways to demonstrate the results of a restoration project is to keep a visual record. Figure 19.4 shows two photos taken from the same location at different times. They illustrate the dramatic changes in the structure of the plant community that can take place in a short period. The diverse buffer strip vegetation serves as a physical barrier to both water and wind movement, provides wildlife habitat, and dramatically changes the aesthetic impressions that visitors have of the site.

A major focus of the Bear Creek watershed restoration project is to demonstrate the capability of the buffer strip to reduce nonpoint source pollution impacts on surface and groundwater and to provide wildlife habitat (Schultz et al. 1995). For example, the ability of the buffer strip to retain sediment is being assessed using a combination of passive collectors (Daniels and Gilliam 1996) and runoff simulation studies. These studies demonstrate that the 21-foot-wide switchgrass component of the buffer strip is capable of reducing sediment contained in runoff from nearly 1,000 parts per million to less than 250 parts per million, a 75% reduction in sediment load.

The potential of the buffer strip to reduce chemical loading to Bear Creek is assessed by using piezometers (measures elevation of water table) and soil suction lysimeters (measures percolation and removal of soluble constituents) to monitor nitrate and atrazine (an herbicide) moving within groundwater and vadose zone (zone between the land surface and the water table) water through the buffer strip.

 

FIGURE 19.3.-Cross section of the multispecies riparian buffer strip at the Bear Creek, Iowa, riparian management site. Photograph was taken in July 1994, the vegetation's fifth growing season.

Results indicate that nitrate concentrations in the vadose zone are much lower across the buffer strip than within the adjacent, cultivated field (Figure 19.5). Whereas concentrations of nitrate-nitrogen within the vadose zone will vary from year to year depending upon crop rotation, average concentrations measured within the vadose zone nearest the stream have never exceeded three parts per million in monitoring conducted between 1994 and 1996. In contrast, concentrations of nitrate-nitrogen measured in the vadose zone within a field cropped to the stream edge showed no reduction nearer the stream. In areas where shallow groundwater contributes significantly to streamflow, this buffering function is important in reducing nitrate loads to the surface water. Atrazine concentrations are similarly reduced across the buffer strip compared with the adjacent, cultivated fields.

Additional research is investigating changes, both in soil quality parameters potentially regulating water movement and in microbial activity that have occurred since the cropped or pastured lands have been planted with buffer strip vegetation. These efforts indicate that the establishment of the perennial vegetation of trees, shrubs, or native grasses has increased soil infiltration capacity, lowered soil bulk density (ratio of the mass of dry soils to the bulk volume of the soil), and improved the quantity and quality of soil organic matter in only 5 years since establishment. Such improvements in soil quality serve as an indicator of the soil's structural and biological integrity, which in turn are related to the status of certain degradative processes and to environmental and biological plant stress (Parr et al. 1992).

 

FIGURE 19.4.-Bear Creek riparian management site. Top photograph shows site in March 1990, prior to buffer strip establishment. The land on the right side of the stream had been in cultivation and the land on the left had been grazed. Bottom photograph shows same site in June 1994. Notice the rapid growth of the riparian vegetation and the dramatic improvement in the condition of the streambank after only five seasons of riparian management.

FIGURE 19.5.-Nitrate-nitrogen concentration within the vadose zone of the cropped field (corn) and within the three zones of the multispecies riparian buffer strip on several dates in 1995.

The habitat value of the buffer strip was assessed by comparing bird species composition within a section of the buffer strip with a contiguous channelized section of stream that had little riparian cover. Results demonstrate that buffer strip establishment has dramatically increased bird species diversity in the short period since planting. On average, only 4 species per day were observed on the channelized stream section whereas 18 species per day were found within the 4-year-old buffer strip. A two-sample comparison indicated that this difference in the number of species was significant (P < 0.05). The total number of bird species observed throughout the study period was also much greater within the buffer strip. Within the buffered stream reach, 30 species were observed, compared -with only 8 species along the channelized stream section. Although community indices are not widely accepted as the sole indicators of habitat complexity, these observations strongly suggest that establishment of the multispecies buffer strip positively influences bird species diversity.

Streambank Stabilization

Several authors have estimated that greater than 50% of the stream sediment load in small watersheds in the Midwest is the result of channel erosion (Roseboom and White 1990). This soil usually consists of small silt and clay particles that are ultimately deposited in rivers, lakes, or back-water areas, choking them with sediment and diminishing their value as habitat for fishes and aquatic macroinvertebrates (Frazee and Roseboom 1993). This problem has been worsened by the increased erosive power of streams that have been channelized and have lost riparian vegetation. The typical solution is to buttress blocks of concrete, rock, wood, or steel along the stretch of the bank that is eroding (Frazee and Roseboom 1993). Such solutions are costly to build and maintain and provide little aquatic habitat.

An alternative streambank stabilization technique is the use of locally available natural materials, such as willow or other live plant material, often in combination with revetments of rock or woody material, such as eastern redcedar. These techniques are often referred to as soft engineering or soil bioengineering (Coppin and Richards 1990). Vegetative means of stabilization protect streambanks in several ways (Klingeman and Bradley 1976). First, the root system helps hold the soil together and increases the overall bank- stability by its binding network structure. Second, the exposed vegetation can increase the roughness resistance to surface flow and reduce the local flow velocities, causing the flow to dissipate energy against the deforming plant and away from the soil. Third, the vegetation acts as a buffer against the abrasive effect of transported materials. Fourth, close-growing vegetation can induce sediment deposition, which reduces stream sediment load and reestablishes the streambank

Several different soil bioengineering techniques have been employed in the Bear Creek watershed. These include the use of willow harvested as posts or stakes in late winter while still dormant and driven into the bank, bundles of live willows (fascines) partially buried along the slope, and biodegradable erosion control fabric anchored with willow stakes or redosier dogwood on bare slopes. Alternatives used to stabilize the base of the streambank include rock and anchored dead plant material, such as eastern redcedar or bundled silver maple. Figure 19.6 illustrates the dramatic improvement in streambank stability that can be achieved over just several months. These bioengineering solutions are very effective and less expensive than traditional streambank stabilization techniques.

Constructed Wetlands

A characteristic of many parts of the upper Midwest is the presence of an extensive network of subsurface tile drainage that has facilitated the conversion of many wetland acres to agricultural uses. Such tile drains often are the primary cause of increases in stream discharge and provide a direct path to surface water for nitrate or other agricultural chemicals that move with the shallow groundwater. In such instances, constructed wetlands integrated into new or existing drainage systems may have considerable potential to remove nitrate from shallow subsurface drainage (Crumpton et al. 1993).

To demonstrate this technology, a small (2,900 square feet) wetland was constructed on the original project site (Risdal farm) to process drainage-tile water from a 12-acre cropped field. The size and shape of the wetland were designed to fit into the 66-foot-wide buffer strip. The wetland was constructed by excavating a low area near the creek and constructing a small berm. The subsurface drainage tile was rerouted to enter the wetland at a point that maximizes residence time of drainage-tile water within the wetland (see Figure 19.1). A simple, gated structure at the wetland outlet provides control of the water level maintained within the wetland. Cattail rhizomes collected from a

 

FIGURE 19.6.-A streambank stabilization structure on Bear Creek. Top photograph taken shortly after completion in May 1995. Prior to stabilization, the streambank was vertical with exposed soil. Techniques employed were rocks for toe stabilization, erosion control fabric to protect the exposed slope, and dormant willow posts. Bottom photograph shows same site in July 1995. Notice the rapid establishment of grasses and the growth of the willows.

 

FIGURE 19.7.-Wetland constructed on the Risdal farm on Bear Creek. Photograph taken in August 1994, a few months after construction. Notice the aquatic vegetation has spread rapidly within the wetland basin. The wetland berm was planted with native prairie vegetation. Water control structure can be seen in the foreground. Buffer strip vegetation can be seen in the background.

 

local marsh and road ditch were planted within the wetland. Growth during the initial season was dramatic. The cattails spread rapidly throughout the wetland and many achieved heights in excess of 6 feet. Big bluestem, Indiangrass, gray-headed coneflower, and black-eyed Susan were planted on the constructed berm to provide vegetation diversity. Establishment of these native prairie forbs was very successful; all species flowered by the second year. Figure 19.7 shows the rapid establishment of vegetation within the first months after construction.

Monitoring and ongoing research--Water samples at the inlet and outlet of the wetland are collected using automated water samplers. In 1995, inflow concentrations of nitrate-nitrogen in the drainage-tile water fluctuated between 7 and 11 parts per million (Figure 19.8). In contrast, outflow concentrations were lower during most exceptions were during May and early July when large precipitation events increased drainage-tile discharge substantially and reduced the residence time of nitrate-laden waters within the wetland. Precipitation during the months of July and August 1995 was substantially below normal. As a result, outflow from the wetland ceased by 1 September, and the wetland was dry shortly thereafter.

 

FIGURE 19.8.-Concentration of nitrate-nitrogen in wetland inflow and outflow during 1995. The field being drained was in soybeans.

Experimental studies have demonstrated the considerable capacity of freshwater wetlands to remove nitrate (Crumpton et al. 1993) and have confirmed that denitrification is the dominant removal process for externally loaded nitrate (Isenhart 1992). These studies also have demonstrated that wetlands containing a large amount of standing vegetation and a large buildup of decaying plant litter will be more efficient in nitrate removal, given sufficient contact time between nitrate-laden water and the substrate. This indicates that the Risdal wetland will likely become more efficient at removing nitrate after several growing seasons and may take several years to reach a steady state with respect to its nitrate removal capacity.

The ratio of the wetland surface area to the area of crop field drained for the Risdal wetland is 1:180. Previous studies suggest that a mature, 1-acre wetland could remove significant amounts of nitrate from waters draining approximately 100 acres of corn to which moderately high nitrogen levels have been applied (Isenhart 1992; Crumpton et al. 1993). The Risdal wetland is, therefore, below this benchmark ratio, and it remains to be seen what the maximum retention capacity for nitrate will be once the wetland reaches maturity.

Rotational Grazing Systems

The gently undulating, highly fertile soils of the Midwest allow development of large crop fields. Because of the value of this land for crop production, livestock grazing is often conducted in a narrow belt within the riparian zone, where cultivation with large equipment may be difficult. As a result, livestock have a dramatic impact on streambanks, riparian zone vegetation, and surface water quality. The use of rotational grazing, with controlled access to the stream, can reduce these livestock impacts. We have just begun to study this last component of the riparian management system model. Comparisons of streambank stability are being made among paddocks (enclosed pasture areas) that totally restrict livestock access to the channel, paddocks that provide very limited direct access to the channel, and paddocks where complete access is allowed during the short periods of grazing. Restricted cattle access should improve water quality and provide better instream habitat.

ADAPTIVE MANAGEMENT

Development of the riparian management system within the Bear Creek watershed is an ongoing process incorporating several actions. The initial concept and design was developed by an interdisciplinary team of scientists and was based on the emerging recognition that rivers and their floodplains are so intimately linked that they should be understood, managed, and restored as integral parts of a single ecosystem (NRC 1992a). Recognizing this, the interdisciplinary team decided to initiate a watershed management project on a real-world agricultural basin and to manage the landscape by using native plant communities to create or restore riparian buffer zones that would complement field-scale practices to reduce nonpoint source pollution. An idealized model that was hypothesized to accomplish the functions of natural riparian zones of the region was developed. Buffer system functions are assessed through experimental work with intensive process monitoring. As more of the process mechanisms and rates are identified, modifications to the model are made and incorporated into subsequent buffer zone establishment.

The social acceptance of the riparian management model is assessed through the use of surveys, focus groups, and one-on-one information exchange. A better understanding of landowner objectives and economic considerations has resulted in numerous variations of the model system. What initially began as just the buffer strip component of the system now includes the three other components: streambank stabilization, constructed wetlands, and rotational grazing. This flexibility is designed to encourage adoption of the management practices by satisfying landowner goals and concerns as well as fitting specific biogeophysical conditions of the site. For example, the buffer strip component of, the model can be modified by using different species combinations and by varying the width of each zone. Although such variation in design may not be optimal for water quality or wildlife benefits, the flexibility is important if it means that a landowner is accepting the concept. After the landowner has had experience with a smaller system, he or she may be willing to increase the size and effectiveness of the buffer or add additional system components.

Technology transfer efforts are geared toward quickly getting the results and information into the hands of landowners and natural resource professionals. This is accomplished through on-site tours, field days, self-guided walking tours, videos, and extension bulletins. Other methods of information dissemination include presentations at meetings of natural resource professionals, conservation groups, and local civic organizations, articles in local newspapers and trade publications, and publications in refereed journals. Local ownership of the restoration effort is encouraged through the development of voluntary citizen action teams that assist in buffer strip establishment, water quality monitoring, and construction of wildlife nesting boxes. Finally, training workshops are being organized for agricultural and natural resource professionals to help disseminate the information and validate results.

A challenge that remains is the uncertainty about the level and extent of restoration needed to effect change at the watershed level. With limited resources and a mosaic of privately owned land, restoration efforts have to be targeted at willing landowners within critical areas of the Bear Creek watershed. On-going modeling efforts will assist in making predictions about the extent of restoration required to improve the biotic integrity of the aquatic resources.

To date, the Bear Creek project lacks an accurate accounting of all benefits associated with the riparian zone management efforts (e.g., aesthetics, wildlife enhancement, and filtering of nutrients and sediments). Farmers and citizens in the watershed clearly prefer a shared responsibility for implementing riparian best management practices. With additional details on system function and valuation of extra market benefits, such as nonpoint source pollutant reduction and wildlife habitat and aesthetic enhancement, landowners will be more willing to install riparian best management practices, especially if cost share and technical assistance are available. Our research and demonstration program stresses voluntary adoption versus regulators approaches of buffer strip installation. Regulation usually sets rigid parameters that do not apply well to the wide range of conditions encountered.

PROSPECTS FOR THE FUTURE

Prospects for the future can be viewed from a watershed restoration perspective as well as a research and model development perspective. The former is specific to the restoration of the Bear Creek watershed. The research team is in the process of identifying, the critical reaches of Bear Creek at which to target restoration, and work will continue to identify willing landowners and sufficient cost-share opportunities. Most landowners do not want to install the systems themselves but are willing to rely on consultants. Thus there is a need to identify restoration consultants well skilled in the design, installation, and maintenance of these systems. Hands-on training workshops are being organized with the sponsorship of nongovernment organizations such as Trees Forever and government organizations such as the Natural Resources Conservation Service and the Iowa Department of Natural Resources.

From the research and model development perspective, several pieces of information must be developed or refined. Especially critical is the establishment of rates for critical biological and physical processes of the system, for example, the relative importance of plant uptake and denitrification as the major mechanisms of nitrate uptake (Hill 1996). It will be important to generalize information gained within specific riparian zones to the watershed level. Also needed is a detailed assessment of the ability of the system to improve the biotic integrity of the aquatic resources. To date, established riparian management systems in the Midwest are not extensive enough or old enough to assess changes in factors regulating the biotic integrity of the aquatic ecosystems. These factors include the ability of the management systems to regulate instream temperature and dissolved oxygen concentrations through shading, to provide energy resources through annual inputs of organic matter, and to provide instream habitat diversity. One of the major research goals for the Bear Creek project is to restore enough miles of stream length so that these assessments can be made.

Riparian management models will need to be integrated with farm planning models to coordinate conservation measures required to reduce nonpoint source pollution. Also, further definition of the human constraints on management system adoption will allow for the targeting of education efforts or for the need to change the model to address socioeconomic and political realities.

Ultimately, it is intended that ongoing work within the Bear Creek watershed will contribute to a comprehensive agricultural watershed management strategy for the midwestern corn belt. To accomplish this, the project must act as a demonstration site for landowners, a demonstration and training site for natural resource managers, and a research site for scientists developing and testing a riparian management system model under real-world conditions.

ACKNOWLEDGMENTS

Support for this work is from the Leopold Center for Sustainable Agriculture and from the Iowa Department of Natural Resources through grants from the U.S. Environmental Protection Agency under the Federal Nonpoint Source Management Program (Section 319 of the Clean Water Act); the U.S. National Research Initiative Competitive Grants Program m, U.S. Department of Agriculture Award 95-37102-2213; the Agriculture in Concert with the Environment program, jointly funded by the U.S. Department of Agriculture Cooperative State Research Education and Extension Service and the U.S. Environmental Protection Agency under Cooperative Agreement 91-COOP-1-6592; and Pheasants Forever. This is a contribution of the Iowa Agriculture and Home Economics Experiment Station, Ames, Project 3209 and supported by Hatch Act and state of Iowa funds.

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