Identifying Riparian Zones Best Suited to Installation of Saturated Buffers: A Preliminary Multi-Watershed Assessment

Saturated riparian buffers are a new type of conservation practice that divert subsurface tile drainage water from direct discharge to surface water into distribution pipes that discharge the tile water into riparian soils. This enables natural processes of biological uptake and denitrification to decrease nutrient loads that are being lost from croplands via tile drains, reducing water quality impacts from agriculture at relatively little cost. This chapter suggests and evaluates draft criteria that identify riparian zones within a watershed that are suited to installation of saturated buffers. Soils criteria, evaluated using soil survey information, include subsurface accumulations of soil organic matter (SOM) (\u3e 1% SOM at 0.75–1.2 m depth), relatively fine-textured subsoils (\u3c 50% sand at 0.75–1.2 m depth), and a shallow water table (\u3c 1 m depth) April through June. These criteria highlight riparian locations where soil conditions should enhance nutrient removal. Criteria are also proposed to avoid locations where streambank failure and/or inundation of crops adjacent to the buffer may occur, which are evaluated using high-resolution digital elevation models, now widely available through LiDAR (light detection and ranging) surveys. The criteria were evaluated in three Midwestern HUC-12 watersheds dominated by fine-grained glacial deposits. Results showed topographic criteria were more restrictive than soils criteria, especially in the flattest landscapes, but 30 to 60% of streambank lengths in the test watersheds were deemed suitable to installation of saturated buffers. This evaluation contributed to inclusion of a saturated buffer siting tool in the Agricultural Conservation Planning Framework (ACPF). Local information is needed to design this practice to fit site conditions

Emission of the greenhouse gas nitrous oxide from riparian forest buffers, warm-season and cool-season grass filters and crop fields

Paper presented at the 11th North American Agroforesty Conference, which was held May 31-June 3, 2009 in Columbia, Missouri.In Gold, M.A. and M.M. Hall, eds. Agroforestry Comes of Age: Putting Science into Practice. Proceedings, 11th North American Agroforestry Conference, Columbia, Mo., May 31-June 3, 2009.Denitrification is recognized as the major mechanism for reducing nitrate in riparian buffers and thus diminishing non-point source pollution (NPS) of surface water bodies subject to high nitrogen loads. However, increasing denitrification rates in riparian buffers may be trading the problem of NPS pollution of surface waters for atmospheric deterioration and increased global warming potential because denitrification produces nitrous oxide (N2O), a greenhouse gas also involved in stratospheric ozone depletion. It is therefore important to quantify the emissions of N2O from different kinds of vegetated riparian buffer systems, and identify ways to minimize emissions while simultaneously maximizing denitrification. We measured N2O emissions from soils; nitrate (NO3--N) and dissolved N2O in groundwater; and soil properties in riparian forest buffers, warm-season and cool-season grass filters, and a crop field located in the Bear Creek watershed in central Iowa. Results suggest that N2O emissions from soils in all riparian buffers were significantly less than in the crop field, but no differences among types of riparian buffers were observed. Nitrate in outflow groundwater of riparian buffers was significantly lower than in inflow groundwater of riparian buffers. However, dissolved N2O in inflow and outflow groundwater of riparian buffers were not significantly different from one another. These results are useful in developing management protocols for riparian forest and other perennial vegetation practices for NPS pollution attenuation and additional multiple benefits.Thomas M. Isenhart (1), Dong-Gill Kim (2), and Richard C. Schultz (1) ; 1. Natural Resource Ecology and Management, Iowa State University, Ames, IA, 50011. 2. Department of Civil and Environmental Engineering, University College Cork, Cork, Ireland.Includes bibliographical references

High stage events and stream bank erosion on small grazed pasture stream reaches in the rathbun lake watershed, southern IOWA, USA

Stream bank erosion in agricultural landscapes is a major pathway for non-point source sediment and phosphorus loading of receiving waters. Previous studies have shown direct and indirect effects of land use on stream bank erosion, and identified high erosion rates within riparian pastures. One potential impact of agricultural land-use on stream bank erosion is the alteration of stream stage characteristics, including an increase in frequency of high-stage events over short periods of time (forming flash hydrographs). The objective of this study was to assess the relationship between the number of high stream stages and corresponding stream bank soil erosion. The study was conducted in six grazed pasture stream reaches within the Rathbun Lake Watershed, a reservoir on the Chariton River located within the Southern Iowa Drift Plain. The erosion pin method was utilized to measure the change in stream bank erosion in response to differences in the number of high stream-stage events, which were monitored by pressure transducers. The measured seasonal bank erosion rates were correlated with the different stream stages data to assess their impact on stream bank erosion. Based on the different model assumptions, there were generally strong linear relationships between high stage and bank erosion. Approximately 75% of the variability in stream bank erosion rates was directly linked to the number of high stages/erosive stream flow depths. Conservation practices that reduce these erosion rates will be those that increase soil-water infiltration, reduce the frequency of high stream flow events and increase bank stability through perennial vegetation cover or reducing disturbance within the riparian zone

Theme Overview: Agriculture and Water Quality in the Cornbelt: Overview of Issues and Approaches

Resource /Energy Economics and Policy, Q25,

Agricultural Conservation Planning Framework: 1. Developing Multipractice Watershed Planning Scenarios and Assessing Nutrient Reduction Potential

Spatial data on soils, land use, and topography, combined with knowledge of conservation effectiveness, can be used to identify alternatives to reduce nutrient discharge from small (hydrologic unit code [HUC]12) watersheds. Databases comprising soil attributes, agricultural land use, and light detection and ranging–derived elevation models were developed for two glaciated midwestern HUC12 watersheds: Iowa’s Beaver Creek watershed has an older dissected landscape, and Lime Creek in Illinois is young and less dissected. Subsurface drainage is common in both watersheds. We identified locations for conservation practices, including in-field practices (grassed waterways), edge-of-field practices (nutrient-removal wetlands, saturated buffers), and drainage-water management, by applying terrain analyses, geographic criteria, and cross-classifications to field- and watershed-scale geographic data. Cover crops were randomly distributed to fields without geographic prioritization. A set of alternative planning scenarios was developed to represent a variety of extents of implementation among these practices. The scenarios were assessed for nutrient reduction potential using a spreadsheet approach to calculate the average nutrient-removal efficiency required among the practices included in each scenario to achieve a 40% NO3–N reduction. Results were evaluated in the context of the Iowa Nutrient Reduction Strategy, which reviewed nutrient-removal efficiencies of practices and established the 40% NO3–N reduction as Iowa’s target for Gulf of Mexico hypoxia mitigation by agriculture. In both test watersheds, planning scenarios that could potentially achieve the targeted NO3–N reduction but remov

Bird species diversity in riparian buffers, row crop fields, and grazed pastures of two agriculturally

Paper presented at the 11th North American Agroforesty Conference, which was held May 31-June 3, 2009 in Columbia, Missouri.In Gold, M.A. and M.M. Hall, eds. Agroforestry Comes of Age: Putting Science into Practice. Proceedings, 11th North American Agroforestry Conference, Columbia, Mo., May 31-June 3, 2009.A design goal associated with most riparian buffer systems is the enhancement of wildlife habitat. To determine whether this goal was being met, we compared breeding bird composition at five sites, including riparian buffers, nearby row crop fields, and an intensively grazed pasture along Bear Creek and Long Dick Creek in north-central Iowa, USA. The riparian buffers consisted of native grasses, forbs, and woody vegetation and represented three different ages (14+, 9, and 2 years old). At each site, 10 min point counts for breeding birds were conducted using 50 m fixed radius plots, which were visited eight times between May 15 and July 10, 2008. A total of 54 bird species were observed over all of the study sites. The installed riparian buffers incorporated in this study had higher bird abundance, richness, and diversity than the crop and pasture sites. The fewest species were detected within row crop fields (15 species) while the most species were observed on the oldest riparian buffer (42 species); intermediate numbers were observed on the 9 year-old (27 species) and 2 year-old (28 species) buffers and the pasture (23 species). Our results suggest that re-establishing native riparian vegetation in areas of intensive agriculture will provide habitat to a broader suite of bird species. In comparison to row crop and grazing land, the buffers contain a greater diversity of vegetative structure in both horizontal and vertical dimensions. Many birds are known to respond positively to such habitat heterogeneity.Sara A. Berges (1), Lisa A. Schulte (1), Thomas M. Isenhart (1), and Richard C. Schultz (1) ; 1. Department of Natural Resource Ecology and Management, Iowa State University, 339 Science II, Ames, IA 50011.Includes bibliographical references

Relation of Riparian Buffer Strips to In-Stream Habitat, Macroinvertebrates and Fish in a Small Iowa Stream

Macroinvertebrate and fish habitat is often degraded as a result of agriculture. Riparian buffer strips are commonly used to counteract the negative effects of agriculture in headwater streams. We assessed the relation of multi-aged riparian buffer strips to in-stream habitat, macroinvertebrate and fish assemblages in an Iowa stream. In-stream habitat, macroinvertebrates, and fish were sampled from two buffered sites and two unbuffered sites, with the greatest substrate, water depth, and velocity heterogeneity occurring in buffered sites. The highest macroinvertebrate richness (11) as well as fish species richness (14), diversity (1.99) and IBI score (37) were found in the site buffered the longest. Habitat heterogeneity and fish community richness and diversity were greater in buffered sites than unbuffered sites making them possible indicators with which short-term stream recovery can be measured

Riparian forests with and without grass filters as buffers of concentrated flow from crop fields

Paper presented at the 11th North American Agroforesty Conference, which was held May 31-June 3, 2009 in Columbia, Missouri.In Gold, M.A. and M.M. Hall, eds. Agroforestry Comes of Age: Putting Science into Practice. Proceedings, 11th North American Agroforestry Conference, Columbia, Mo., May 31-June 3, 2009.A vegetation inventory within naturally occurring forested riparian buffers (natural forest buffers) and a survey comparing buffering of concentrated flow paths (CFPs) by natural forest buffers with and without planted grass filters was conducted along first and second order streams in three northeast Missouri watersheds. Seven natural forest buffers without grass filters were inventoried and found to be composed of dense stands of mixed tree species with a forest floor cover comprised largely of unrooted woody plant debris, which does not adequately buffer concentrated runoff. Seventy-four CFPs were found in row crop fields along 10 natural forest buffers with or without grass filters established using USDA conservation practice standards. Natural forest buffers without grass filters dispersed 80 [percent] of CFPs before they reached the stream, while those with grass filters dispersed 100 [percent]. We estimated 473 metric tons of sediment moved to the buffers/filters via CFPs since last tillage. Nine of the 74 CFPs passed completely through natural forest buffers without grass filters, and accounted for 97 metric tons of the total estimated 473 metric tons. The average width of breached forest buffers without grass filters was 12.8 m, while the width of those not breached was 17.9 m. Average width of cool-season grass filters (CSGF) adjacent to forest buffers was 17.6 m, while average width of warm season grass filters (WSGF) was 22.1 m. These data, along with previous research, suggest that adding a grass filter along narrow natural forest buffers would improve water quality by reducing sediment loss to streams.K.W. Knight (1), R.C. Schultz (2), C.M. Mabry (2), T.M. Isenhart (2), and L. Long (2) ; 1. The Nature Conservancy, Skagit River Office, 410 N. 4th St., Mt. Vernon, WA 98273. 2. Dept. of Natural Resource Ecology and Management, Iowa State University, 339 Science II, Ames, Iowa 50011-3221.Includes bibliographical references

Relation of Riparian Buffer Strips to In-Stream Habitat, Macroinvertebrates and Fish in a Small Iowa Stream

Macroinvertebrate and fish habitat is often degraded as a result of agriculture. Riparian buffer strips are commonly used to counteract the negative effects of agriculture in headwater streams. We assessed the relation of multi-aged riparian buffer strips to in-stream habitat, macroinvertebrate and fish assemblages in an Iowa stream. In-stream habitat, macroinvertebrates, and fish were sampled from two buffered sites and two unbuffered sites, with the greatest substrate, water depth, and velocity heterogeneity occurring in buffered sites. The highest macroinvertebrate richness (11) as well as fish species richness (14), diversity (1.99) and IBI score (3 7) were found in the site buffered the longest. Habitat heterogeneity and fish community richness and diversity were greater in buffered sites than unbuffered sites making them possible indicators with which short-term stream recovery can be measured

A Tale of Three Watersheds: Nonpoint Source Pollution and Conservation Practices across Iowa

Resource /Energy Economics and Policy, Q25,