Michelle Soupir presenting at Black Hawk Lake Field Day Sept. 15, 2016
Note: Today’s guest blog was written by Michelle Soupir, Leigh Ann Long, Katherine van der Woude. They are conducting a monitoring and research project in Black Hawk Lake watershed in Sac County. Michelle presented at our Iowa Learning Farms field day on September 15th in Lake View. It was a great chance to share with area folks what they have been learning about water quality in the small streams feeding Black Hawk Lake and we wanted to share it with you too!
We have been collecting water samples from three subwatersheds in the Black Hawk Lake watershed since March 2015, and the data we have clearly shows the positive impact that conservation practices have on water quality.
Katherine van der Woude collects samples from their automated samplers and meets a new amphibian friend near Black Hawk Lake.
One part of our work is comparing two subwatersheds with similar soils and of similar size, about 450 acres each.
Subwatershed 12 has various conservation practices implemented over nearly all of its area including: cover crops, terraces, nutrient management plans and CRP on both sides of the stream near where we collect our samples. The second location, subwatershed 11 has only about 25% of the subwatershed in conservation practices. See map below.
2015 was a wet year with nearly 35 inches of rainfall in the watershed, compared to a long term average of 20 inches. Much of the extra rainfall came as highly intense storms, which has an impact on soil erosion and nutrient movement.
From the site with fewer practices (11), average nitrate loading in 2015 was 153 lbs/ac, while the site with lots of conservation practices (12) had an average load of 115 lbs/ac. This calculated to about a 33% increase in nitrate load from the site without conservation practices.
Total phosphorus loads were also higher from the site without conservation practices (11) at approximately 2.7 lbs P/ac., with 92% of the losses occurring during storm events. Two-thirds of those total P losses came from a single storm event in June 2015 that delivered 4.1” rainfall in 2 ½ days. In the subwatershed 12, the average total P loads were nearly half of those from the site with fewer practices.
And finally, enormous differences were observed between the total suspended solids; 2,900 lbs of soil per acre were lost from subwatershed 11, but less than 89 lbs/ac were lost from the site with many conservation practices. Again, most of the soil losses came from storm events.
Another way to look at it:
These results show what a tremendous difference conservation practices can make and how important it is to use many different approaches to meet water quality goals.
For more information on the Black Hawk Lake Watershed Water Quality Project follow them on Facebook and Twitter. Questions about the monitoring project can be directed to Michelle Soupir at email@example.com.