Variable-width buffers to reduce sediment pollution from potato production on steep slopes of Black Brook Watershed using AgBufferBuilder

Transcription

1 Variable-width buffers to reduce sediment pollution from potato production on steep slopes of Black Brook Watershed using AgBufferBuilder Josée Owen and Sheldon Hann Agriculture and Agri-Food Canada Potato Research Centre, Fredericton, NB and Michael Dosskey United States Department of Agriculture National Agroforestry Centre, Lincoln, NE

2 Once upon a time, in Canada Saint John River Farmland in the river valley

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8 A few things we all know: Potato farming involves much soil disturbance Disturbed soil is easily eroded, especially during heavy rain or snow melt Riparian buffers can intercept sediment, nutrients and agrochemicals before they enter the water Regulations ask for fixed setbacks from watercourses rather than variable-width riparian buffer Planting buffers costs money Farmers don t have much money

9 A few things we d like to know: How effective are the existing buffers? Where should I plant buffers? If I only have a little money for buffers, where should I plant so that my $ investment has the greatest impact? Is it better for each farmer to plant buffers, or for a community to plan buffers at a landscape level?

10 Objectives To evaluate and modify the software AgBufferBuilder 1.0 to offer growers a decision-support tool for recommending where variable-width buffers can be planted to the greatest benefit Evaluate of the AgBufferBuilder 1.0 extension (through the ArcGIS 10.0 platform) on the Black Brook Watershed Evaluate trapping efficiency of existing vegetative buffers. Evaluate trapping efficiency of model-derived vegetative buffers

11 AgBufferBuilder 1.0: A Filter Strip Design Tool for GIS Developed by United States Department of Agriculture and University of Kentucky ArcGIS extension for designing and assessing vegetative filter strips around agricultural fields Combines digital imagery, elevation data, cropping system and soil information to assess the efficacy of existing buffers Develops raster datasets that identify the locations of potential buffers that result in a user-defined efficiency Primarily a research tool: has not been validated in a production context

12 Study Area: Black Brook Watershed 1,450 ha, approx. 65% agricultural About 50% of ag land is in potatoes annually Slopes from 2-9%, some exceeding 15% Annual precipitation is 1130mm (25% as snow) Water-related soil losses can exceed 20 tonnes/ha annually associated with up-and-down slope potato cultivation without erosion protection > 50% of the farmland in the BBW have implemented some BMPs

13 Black Brook Watershed is a long term model watershed. Best Management Practices are represented here much more than in other Potato Belt areas. Diversion terraces with vegetative buffers, and grassed waterways

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15 AgBufferBuilder 1.0: Input Data Digital Imagery: Orthophoto ( ) (MrSID 1m resolution) Elevation Data: Canadian Digital Elevation Data (1:50,000 or 8-23 m resolution)

16 AgBufferBuilder 1.0: Input Data Land Use Records: 2011 land use records were used to verify field boundaries. AAFC Weir Sub-basins: Weir sub-basins were used as natural breaks in the topography.

17 AgBufferBuilder 1.0: Data Analysis Input data was imported and re-projected in ArcGIS to maintain data compatibility AgBufferBuilder 1.0 extension was loaded Each weir sub-basin was delineated as the Field Margin dataset Existing buffers/bmps were delineated as the Buffer Assessment dataset The Buffer Assessment dataset is used by the AgBufferBuilder extension to assess existing buffers and provide a trapping efficiency value (%) The data analysis results consist of two raster datasets: the current buffers that were identified in the Area of Interest (AOI) with the trapping efficiency value the model-derived buffers that provide 75% trapping efficiency

18 AgBufferBuilder 1.0: Results The derived buffers were produced by using the following parameters Type of pollutant: Sediment Soil texture of the surface soil layer: Class I -Medium texture materials (SC, SiL, L, VFSL) Soils associated with BBW include Grand Falls, Holmesville, Interval, Muniac, Seigas and Undine (range from SL to SiL) USLE C-Factor: 0.50 Plow tillage after corn or chisel after soybeans Trapping efficiency: 75%

19 BBW Weir Sub-basins: Weir 2 Analysis Buffer size (ha) Calculated efficiency Current buffers % Buffers calculated to provide 75% efficiency %

20 BBW Weir Sub-basins: Weir 3 Analysis Buffer size (ha) Calculated efficiency Current buffers % Buffers calculated to provide 75% efficiency %

21 BBW Weir Sub-basins: Weir 6 and Weir 7 Analysis Buffer size (ha) Calculated efficiency Current buffers 0.5 0% Buffers calculated to provide 75% efficiency %

22 BBW Weir Sub-basins: Weir 6 and Weir 7 Landscape scale considerations Analysis Buffer size (ha) Calculated efficiency Current buffers of Weir 6 and Weir % Analysed separately % Analysed together %

23 Analysis Buffer size (ha) Calculated efficiency Current buffers 6.0 9% Buffers to provide 75% efficiency % Scenario % Scenario %

24 The social side of environmental responsibility Potato growers in this region are very competitive with each other Potato industry is undergoing a contraction financial bottom line will determine who will be able to grow for shrinking processing prices Many landowners in the watershed Fields of one grower may drain into land of another grower Buffers necessary for one owner s fields may sometimes need to be placed in another owner s field Few incentives for growers to plant buffers

25 Effecting real change Majority of New Brunswick s population is downstream A thriving potato industry is important to the economy Clean water is a public benefit Tools such as AgBufferBuilder can be used to show where welldesigned variable-width buffers would work to best effect Projects such as this may provide tools and rationale for public programming Skilled land-use planner, able to design effective buffers Working with a community of growers In a participatory approach Supported by incentives

26 Conclusions Software was designed for field-by-field use, but could have greater use as a landscape-level planning tool Uses imagery, elevation data and land use records allowing for a better understanding of the interactions between topography and erosion potential Could eventually be a tool to support policy changes to support variable width buffers and programs to support landscape planning Is theoretical until we do the next steps of validating the model

27 Conclusions Recommends only size and placement of buffers Make-up of buffers affects efficiency Additional tools required to guide species selection, spacing, establishment AgBufferBuilder can be used to design buffers to prevent sediment and associated agrochemicals from reaching watercourses It does not address the important issue of how to keep sediment in the field where it belongs

28 AgBufferBuilder 1.0: Future Considerations The model needs validation We need to confirm that the suggested buffers, if planted, deliver the suggested results We intend to mount a project to validate the model Particular attention to snowmelt User interface may need adaptation Data choices available now reflect only US mid-west agriculture

29 Thank you for your attention! Acknowledgements Developer of AgBufferBuilder: Dr. Mike Dosskey of the USDA National Agroforestry Center GIS work: Sheldon Hann, AAFC, Agroforestry and Agronomy Research Team