Nutrient and sediment concentrations and corresponding loads during the historic June 2008 flooding in eastern Iowa

U.S. Department of the InteriorU.S. Geological Survey

June 2008 flooding in eastern Iowa

L.E. Hubbard 1, Kolpin, D.W. 1, Kalkhoff, S. J. 1, Robertson, D. M. 2

(1) U.S. Geological Survey, Iowa Water Science Cent er(2) U.S. Geological Survey, Wisconsin Water Science Center

6/12/2008 Cedar Rapids 3rd Ave

6/13/2008 Cedar Rapids

6/12/2008 Cedar RapidsPhoto by Jason McVay

6/13/2008 Cedar River at Hwy 30Photo by Scott Strader

6/9/2008 Charles City, IA (Cedar River) Photo by Jon Nania

Coralville, IA (Iowa River)

� December 2007 to May 2008 - 2 nd wettest in the period of record for eastern Iowa (1895 to 2008) (NCDC, 2008)

Background

Percent soil saturation May 28, 2008Source: Iowa Mesonet: Iowa Daily Erosion Project

Map by Kasey Hutchinson

Background

� June 2008 - the 2 nd wettest June in the period of record for Iowa (1895 to 2008) (NCDC, 2008)

Rainfall May 29 to June 12, 2008Source: National Weather Service

Map by Kasey Hutchinson

Background

Map by Dave Eash

Background

� Iowa 1 st in harvested acreage and corn for grain production; 2 nd in soybean production (2004) (USDA NASS, 2005)

� Over 59% of Iowa is used for corn and soy production (USDA NASS, 2008)production (USDA NASS, 2008)

� Iowa is a major contributor of nutrients/sed. to the Mississippi River (Goolsby et al, 1999; Royer et al., 2006; Alexander et al., 2008)

� 1993 flood - a missed opportunity

Sampling

� Near peak-flow (within 24 hrs) water samples collected at 29 locations in Iowa during June 2008; many locations had multiple samples

� Grab samples from the centroid of flow –� weighted bottle sampler and a 1 Liter baked amber � weighted bottle sampler and a 1 Liter baked amber

glass bottle; 2 samples Equal Width Increment (EWI) (USGS, 2006)

� Concurrent grab samples and EWI were collected at two sites at different discharges to document sample bias

Methods

� Samples were analyzed for total phosphorus (TP), total nitrogen (TN), nitrate, ammonia, orthophosphate (ortho-P), and suspended sediment (SS)

� Data Analysis� Data Analysis� Concentrations and Instantaneous loads� 16-day transport yields - four Mississippi River

tributaries� Percentage of the annual yield - three sites

according to two different study estimates.

10

15

20

25

Con

cent

ratio

n (m

g/L)

Nitrate (mg/L)

Total Nitrogen (mg/L)

SS*100 (mg/L)

0

5

Con

cent

ratio

n (m

g/L)

1 2-31 11 4 6 2-3

† indicates EWI sample

0.4

0.6

0.8

1

1.2

1.4C

once

ntra

tion

(mg/

L)

Ammonia (mg/L)

Ortho-p (mg/L)

Total Phosphorus (mg/L)

0

0.2

0.4

Con

cent

ratio

n (m

g/L)

† indicates EWI sample

1 2-31 11 4 6 2-3

Results

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Con

cent

ratio

n (m

g/L)

Ammonia

Ortho-p

Total P

0

10000

20000

30000

40000

50000

60000

Load

(kg

/hr)

Ammonia

Ortho-p

Total P

P<0.05

P<0.05

P<0.05

P>0.05

P<0.05

P<0.05

998239 430

48,200

5,580

13,300

0

1 2

0

5

10

15

20

25

30

1 2

Con

cent

ratio

n (m

g/L)

Nitrate

Total N

SS*10

0

1 2

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

1 2

Load

(kg

/hr)

Nitrate

Total N

SS*10

1979-2007 1979-2007

1979-2007 1979-2007

2008 2008

2008 2008

P<0.05

P>0.05

P<0.05

P<0.05

P<0.05

P<0.05

38,40056,000

265,000395,000

416,000

1,980,000

Results – TN Near Peak Daily Yields

Results – TP Near Peak Daily Yields

Results – SS Near Peak Daily Yields

Results� 16-day TN transport load could fertilize

843,000 acres of cropland – over 6 counties � 16- day TP could fertilize 152,000 acres� 16-day SS could fill 143,000 dump trucks

Site Name Discharge TN TP SSSite NameSTAID

Discharge(m3/s)

TN(kg)

TP(kg)

SS(kg)

Wapsipinicon River near De Witt, IA05422000

8,870 4,860,000 163,000 7.48 E7

Iowa River at Wapello, IA05465500

42,600 22,000,000 1,300,000 5.64 E8

Skunk River at Augusta, IA05474000

12,600 4,990,000 408,000 2.72 E8

Des Moines River at Keosauqua, IA05490500

33,900 17,700,000 1,040,000 1.04 E9

Total 98,000 49,500,000 2,900,000 1.95 E9

Results – 16-day Yields

Site NameSTAID

2008 WY

(m3/s)

WY Annual Mean (m3/s) Constituent

Flood 16-day Yield

Annual Yield

Yield (kg/km2)

Goolsby (1999)* Robertson et al. (2009)

Yield (kg/km2)

Flood % of annual yield

Yield (kg/km2)

Flood % of annual yield

Note: the Des Moines River site used in Goolsby et al. (1999) is Des Moines River at Francisville, MO (05490600), approximately 50 km downstream of Keosauqua, IA

STAID (m3/s) (m3/s) Constituent (kg/km ) yield yield

Des Moines River at Keosauqua, IA05470500

529 244

TN 486 1,850 26 1,910 26TP 28.7 64.1 45 73.7 39Nitrate 421 1,690 25 - -Ortho-p 11.3 37.1 30 - -

Iowa River at Wapello, IA05465500

616 267

TN 679 2,290 30 2,210 31TP 40.1 94.9 42 87.2 46Nitrate 546 1,770 31 - -Ortho-p 17.6 62.3 28 - -

Skunk River at Augusta, IA05474000

198 74

TN 447 2,020 22 2,060 22TP 36.5 120.5 30 111.7 33Nitrate 400 1,560 26 - -Ortho-p 14.0 41.7 34 - -

1993 vs. 2008� Daily peak-flow was higher in 2008� Different hydrographs

175,000

200,000

Iowa River at Wapello, Ia

Dai

ly m

ean

disc

harg

e, in

cub

ic fe

et p

er s

econ

d

1993

0

25,000

50,000

75,000

100,000

125,000

150,000

175,000

Dai

ly m

ean

disc

harg

e, in

cub

ic fe

et p

er s

econ

d

Jan Feb Mar Apr May Jun Jul Aug Sep

19932008

Steve Kalkhoff

Summary

� Concentrations may be similar to average concentrations but loads are much larger during extreme events

� Floods very important to average annual yield – 2008 flood up to 46% of average annual – 2008 flood up to 46% of average annual yield!

� Implications of Midwest flooding to the Gulf of Mexico hypoxic zone� Lasting effects of 1993 on the Gulf hypoxic zone� July 2008 hypoxic zone ranks 2 nd

Future Work

� Each flood is different� Need more data – characterizing floods and

modeling� Concentrate on one basin next flood?

Questions?

Laura Hubbardlhubbard@usgs.gov