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 [email protected]
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