|Little CannonRiver E. coli Assessment
By Beau Kennedy, Goodhue County SWCD
We divided the Little Cannon River Watershed into 10 different subwatersheds. A rating was applied to all the active feedlots and septic systems in each subwatershed. For feedlots we used the standard FLEval
methods. This required a site visit to every feedlot within the Little Cannon River Watershed (approximately 120). For septic systems we developed a rating system which was based on the age of the system weighted for its proximity to a water source.
At the outlet of each subwatershed, water samples were taken and sent to the lab for E. coli analysis, except for several subwatersheds that were dry whenever we tried to sample. E.coli is measured in MPN/100ml of sample (MPN = most probable number of colonies).
We were able to give a pollution potential rating to each subwatershed and compare that to the water quality data.
The findings of the study are not completed yet, since we still have another season of stream sample collection.
Once the data from 2008 was compiled, we entered our lab results and ratings into an Arc table where they could be manipulated. To portray the commonalities and differences we sorted the subwatershed by using the basic symbology tool. See Figure 1
. The map colors represent E. coli
numbers – red indicates a higher number of bacteria in the stream samples and green indicates a lower number of bacteria. The white (or dashed) watershed had no samples taken. The numbers are watershed labels.
We utilized the ArcGlobe application for this study as well. We found that ArcGlobe can demonstrate the findings of this study in a way that most programs cannot. By utilizing the track/fly tool, the audience gets a 3D image of where feedlots or septic systems are located in the subwatershed as well as the pollution potential rating. See Figure 2
for a snapshot taken from ArcGlobe. The column symbols are silos, representing a feedlot present at that site. The pushpin symbols are stream sample locations.
Our preliminary E. coli results seem to correlate pretty well with the feedlot assessments done in the subwatersheds. One subwatershed (labeled “4” in the graphic) had the highest FLEval rating AND the highest geometric mean of bacteria in the stream.
On the other hand, the subwatershed labeled “5” had the highest rating for septic assessments, and yet the lowest E. coli numbers. This could be due to the subwatershed’s land use. It is by far the most wooded of the subwatersheds and has the lowest stream temperatures.
After the 2009 sampling season is complete, we should be able to determine which subwatersheds are contributing the most fecal to streams. This way we can concentrate our cost/share and technical assistance efforts in these impaired areas.
The Goodhue County SWCD would like to thank the Goodhue County GIS Department
for their leadership and dedication to the Goodhue County Users Group
. The GIS Department provided the SWCD with various layers we needed for this study including 2’ contours, parcel information, zoning, roads, and high resolution aerial photos. They also provided ArcGIS licensing and the Spatial Analyst extension for our staff. None of these applications would have been possible if it weren’t for the SWCD’s participation in the Users Group.
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