This paper is the first to provide direct measurements of denitrification over the scale of an entire regional aquifer. To achieve this, we added a large amount of existing data (mostly from co-author Brian Katz) to our own sampling of the Floridan Aquifer springs, and developed new ways to use noble gases to develop null predictions of N2 gas concentrations. Basically, we use argon and neon to estimate how much N2 should be in the water, then calculate denitrification (which produces N2 gas) by difference.
This paper also demonstrates the large effect of denitrification on groundwater N isotopes. One reason we care about this is that we use isotopes to identify sources of N: synthetic fertilizers have low or 'light' isotope signatures, while organic waste (from urban and animal husbandry sources) are 'heavy'. , we have to account for these effects or we will get the source wrong.
You can read the Duke press release here, and get the paper here. You can learn more about our other springs research here.