Determining trends is tricky business. You’re looking into the past at water quality data to see if you can discern what has happened. Then you try to see if these changes correlate with something else: local, state, and federal policy; land use changes; advances in technology. The problem we have with this approach here in Iowa is that year-to-year weather variations are large, some would say extreme.

First Quarter nitrate levels in the Raccoon and Des Moines Rivers (at Des Moines) were above average in 2017 compared to the historical record.

Nitrate load summary from January and February 2017.

Detailed data sets for the Raccoon and Des Moines Rivers at Des Moines go back to 1974 and 1982, respectively.

During 2016, IIHR Hydroscience and Engineering along with USGS had 14 real-time nitrate sensors deployed in locations that captured water quality conditions for 82.5% of the water leaving the state of Iowa.

When January nitrate was between 6 and 8 mg/L in the period of 1974-2016, annual nitrate ended up between 4.7 and 8.5, a much tighter window than the entire range of observed annual averages (0.6 to 11.7 mg/L). The overall long term annual average is 6.6 mg/L. Based on this I am predicting a below average-to-average year for Raccoon River nitrate.

Summary of the 2016 Nitrate loads in the Des Moines and Raccoon Rivers.

If Iowa continues to get wetter, which many climate experts predict, relatively modest increases in precipitation could result in disproportionately large increases in nitrate-N loads.

Raccoon and Des Moines River nitrate amounts for November 2016

October Raccoon and Des Moines River Nitrates