Nitrogen-laden runoff - how is this affected by extreme rainfall events in the Midwest?

Climate change brings more extreme rainfall events to the Upper Mississippi River Basin according to the National Climate Assessment.   How much does this contribute to the loss of nutrients from the land and subsequent over-enrichment of our waters?  

Recent research at Iowa State University has shown that the heavy rain events that occur only a few days a year can account for up to a third of the annual nitrogen runoff from farmland in the Mississippi River basin, according to a new study from Iowa State University scientists.  The research, uses innovative computer modeling techniques to quantify nitrogen runoff from land ecosystems into rivers and streams.   This link goes to a summary of that research.  

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Looking in more detail at the full published study, the researchers found that "Overall, >80% of the Basin total runoff and N leaching was from the rising extreme precipitation areas. Basin-wide, extreme precipitation events occurred only 8.6 days year−1 (2.4% of 365 days) on average, but they contributed to approximately one-third of annual total water yields and N yields. This is likely a conservative estimate of the contribution of extreme precipitation events as we only focus on extreme precipitation days without consideration of post-event legacy effects."  

This new understanding of the role of extreme precipitation can inform how changes can be made in fertilizer and manure application to reduce the loss of nutrients.