An Integrated Riparian Management System to Control Agricultural Pollution and Enhance Wildlife Habitat

Animal Production: feed/forage
Farm Business Management: budgets/cost and returns, agricultural finance
Natural Resources/Environment: grass waterways, hedgerows, riparian buffers, soil stabilization, wildlife

Abstract:

[Note to online version: The original report for this project includes graphical figures, tables, and special characters that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact North Central SARE at (402) 472-7081 or ncrsare@unl.edu.]

An integrated riparian management system was developed along a central Iowa stream to demonstrate the benefits of properly functioning riparian zones in the heavily row-cropped Midwestern United States. The system consists of three components; a multi-species riparian buffer strip, soil bioengineering technologies for streambank stabilization, and a constructed wetland to intercept and process non point-source pollutants in agricultural drainage tile water.

The general multi-species riparian buffer strip layout consists of three zones. Starting at the stream bank edge, the first zone includes a 9 m (30 ft) wide strip of 4-5 rows of trees, the second zone is a 4 m (13 ft) wide strip of 1-2 rows of shrubs, and the third zone is a 7 m (22 ft) wide strip of native warm-season grass. This design is important because the trees and shrubs provide perennial root systems and long-term nutrient storage close to the stream while the grass provides the high density of stems needed to dissipate the energy of surface runoff from the adjacent cropland.

Water and chemical movement across the buffer strip are being monitored using a combination of piezometers, tensiometers, and tension lysimeters. Initial results show that nutrient and pesticide concentrations in the unsaturated zone are much lower across the buffer strip than within the adjacent cultivated field. After six years, soil water in the unsaturated zone under the buffer strip never exceeded 3 ppm of NO3--N, or 1 ppb of atrazine, even though concentrations as high as 30 ppm and 8 ppb, respectively, are measured in the cropfield. However, nitrate concentrations in the shallow groundwater are highly variable between adjacent transects, suggesting that nitrate contained within shallow groundwater may be moving preferentially across the buffer strip. We are expanding our efforts to accurately characterize groundwater and chemical movement across the buffer strip.

Several streambank bioengineering technologies are being demonstrated at the project site. The first is a combination of live willow posts and dead, bundled, hardwood revetments. The other is a combination of live willow posts and geotextiles in combination with Eastern red cedar or rock rip-rap for protection of the streambank toe. These installations have been very effective in stabilizing the banks.

A small wetland was constructed to intercept and process agricultural chemicals contained in tile drainage. Nitrate loss rates per square meter of wetland sediment are comparable to those observed in experimental wetlands and are dependent upon temperature and residence time of the pollutant laden water. It is expected that the nitrate removal capacity of the wetland will increase as the wetland matures and accumulates a layer of dead plant material.

Establishment of the riparian management system has dramatically improved the wildlife habitat on the farm. Results demonstrate that nearly four times as many bird species are using the buffer strip than are using an adjacent, non-buffered stream reach.

Technology transfer efforts have been very successful. In the last two years over 30 formal tours (>1,000 persons) have visited the site. A self-guided trail has been established to provide information to visitors to the site. Thirteen papers have been prepared and 53 invited presentations have been made to local, regional and national groups. An extension bulletin series entitled "Stewards of Our Streams" is also being produced.

Project objectives:

The overall objective of this research has been to develop a riparian management system (RiMS) to rehabilitate riparian zones in agricultural ecosystems and to transfer this information to landowners, resource agency personnel, and policy-makers. The integrated management system is intended to restore ecosystem functions associated with a healthy and diverse riparian zone. The system model includes the establishment of a multi-species riparian buffer strip (MRBS) of native tree, shrub, and grass vegetation to control the adverse effects of upland agriculture on stream water quality and to improve wildlife habitat. The initial MRBS was established in 1990 on the Ronald Risdal farm along Bear Creek in central Iowa. The ACE project has provided for the continued development of this site and has allowed for some of the initial quantification of the effects of a MRBS on surface and groundwater quality. In addition, the ACE project has provided for the demonstration of two other components of the RiMS model: soil bioengineering technologies to reduce streambank erosion and constructed wetlands to intercept and process nonpoint source pollution contained in agricultural tile drainage. The result is a unique riparian management system having three separate practices located on the Risdal farm. Other objectives of this project have been to evaluate the effects of the riparian management system on wildlife populations and to evaluate the costs of establishing and maintaining the three components of the RiMS. Finally, the ACE project has provided for extensive technology transfer efforts. The research is being conducted by the Iowa State Agroforestry Research Team and the Agroecology Issue Team of the Leopold Center for Sustainable Agriculture.

Specific objectives of the project are as follows:

Objective 1 - Demonstrate and quantify the ability of the MRBS to filter, transform, and act as a sink for nonpoint source pollutants.

Objective 2 - Develop a small wetland to intercept and process field tile drainage.

Objective 3 - Demonstrate the ability of soil bioengineering technologies to function as a durable and environmentally acceptable system for long-term stabilization of eroding stream banks.

Objective 4 - Evaluate the impact of the MRBS, the constructed wetland, and the soil bioengineering technologies on wildlife habitat and use.

Objective 5 - Evaluate the costs of establishing and maintaining the three components of the RiMS being demonstrated on the Risdal farm.

Objective 6 - Develop appropriate technology transfer materials and activities for farmers, policy-makers, farm groups, and others.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.