chris jones university of iowa-iihr · n yields david, m.b., drinkwater, l.e. and mcisaac, g.f.,...

Chris Jones

University of Iowa-IIHR

NO3-

NH4+ON

ClimateMillett, B., Johnson, W.C. and Guntenspergen, G., 2009. Climate trends of the North American prairie pothole region 1906–2000. Climatic Change, 93(1-2), pp.243-267.

Drainage

N YieldsDavid, M.B., Drinkwater, L.E. and McIsaac, G.F., 2010. Sources of nitrate yields in the Mississippi River Basin. Journal of Environmental Quality, 39(5), pp.1657-1667.

ToleDrinking Water

Toledo, OH

Des Moines, IA

Hypoxia, Aquatic Life

Raccoon River Watershed

• 9389 km2

• 75-80% row crop (corn and soybean)

• Headwaters of N. Raccoon to mouth = 350 km

• Average discharge = 68 m3/sec• Peak discharge = 2000 m3/sec

No major cities above Des Moines

N loss

Kg

/cro

pp

ed

hecta

re

0

20

40

60

80

67 kg/Ha in 2015

Monitoring• 65 Sites total• 7000 Grab Samples• Analytes:

Nitrate-NitrogenTurbidityE coliOrganic and inorganic Carbon

Most monitoring April-July

6 with Flow Gauges where total loads can be determined

Sample Collection and Analysis

Sample Collection:• Volunteers• IA Soybean Staff

Lab Analysis:• conducted at

certified lab

Concentration Trends

• 39 out of 41 sites trending down 1999-2014 (5620 samples total) (Probability < 0.001%)

• Average decline -0.31 mg L-1 yr-1

• 9 sites p < 0.10

• 5 sites p < 0.05

Analysis by A. Seeman, ISA

BootstrappingWe bootstrapped the annual NO3-N concentration trends by adding to the fitted values the residuals whose signs were randomly switched. We then computed the mean/median of a set of bootstrap trends. The procedure was repeated 10,000 times to get a distribution of the mean/median bootstrapped trends.

Overall Trend: -0.265 mg L-1 yr-1

p < 0.05

Analysis by K-S. Chan, UI

Concentration Trends at the Mouth (DMWW)

April-July: -0.31 mg L-1 yr-1

(p=0.098)

Jan-Dec: -0.13 mg L-1 yr-1

(p=0.15)

Loading Trends

• linear regression of Apr-Jul precipvs N load

• SK test for trend on the residuals

• 5 sites, none trending upward

• Jefferson site trending down at -353 Mg Yr-1, p< 0.05

Precipitation-corrected loading trends (Seasonal Kendall) for the five tributary sites where flow gauges are deployed.

-18%

-16%

-22%

-36% -19%

-17%

Flow Weighted Averages at 6 Gauged Locations

1999-2013

total load/total discharge

700 Fields in watershed counties, 2006-2013

Total N inputs increased 13% and Fertilizer N inputs increased 24%!

N Exported in Grain

No increase in N use efficiency

Where’s it going?• Less Denitrification Under Soybean

• More Continuous corn

Less Fall Applied N ?? (MN)

• Tile flow greater ( and greater N Loads?) under soybean, i.e. less tile flow under corn

• Tillage Component?

N returned in Crop Residue1

99

8

20

00

20

02

20

04

20

06

20

08

20

10

20

12

Conclusion: Decline in Soybean Area Linked to Declining (or at least unchanging) River Nitrate

Modeling Raccoon River N 1974-2013Flow-Weighted Average Concentration

Previous Year

Analysis by G. Villarini, UI

Conclusions•Incremental improvement likely, but current condition

still unacceptable to most

•Transformational Improvements? Cover Crops?

•Better management of Soy may have disproportionately positive effects on Water Quality

•Monitoring and credible data will be critical for making policy and spending conservation dollars

•Return to small grains, alfalfa, clovers?

Acknowledgements

Raccoon River Sediment

Turbidity vs TSS

Supply Limitations vs Transport Limitations

• 1930-2010: $294B spent on conservation programs

• $75B on Technical Assistance (26%)

• $219B on Financial Assistance (74%)

Technical Assistance is far more effective

than Financial Assistance

Questions?