Nitrate Load & Concentration

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

April May June July August September October

Nit

rate

-N C

on

cen

trat

ion

(m

g/L

)

Nit

rate

-N L

oss

(lb

s/ac

re/d

ay)

Nitrate-N Average Loss (lbs/acre/day) Nitrate-N Average Concentration (mg/L)

Water Quality Practice Selection

Need to select solutions which are

most effective in May, June & July

Nitrate Concentration vs Nitrogen Fertilization Rate

0

10

20

30

40

50

60

100 120 140 160 180 200 220 240 260 280

Nit

rate

-N C

on

cen

trat

ion

(m

g/L

)

Nitrogen Fertilizer Rate (lbs/acre)

All Fields

Cover Crop

Nitrate by Landform

Lyons Creek as a Representative Tile-drained Landscape

• 42 km2 watershed in Boone River basin

• 90% corn and soybean cultivation

• Three drainage districts investigated:

1. LCR3T (600 ha)

2. LCR4T (250 ha)

3. LCR5T (1096 ha)

Objective: What is the suitability of

using Lyons Creek in a paired

watershed study to test the

effectiveness of BMPs in tile-

drained landscapes?

Tile Drainage Contributes to High Nitrate

Concentrations in Streams

Nitrate concentrations

exceed MCL of 10 mg/l 90%

of time in central Iowa tile

drainage systems

Schilling et al., Ecol Eng. 2012

0.001

0.01

0.1

1

10

100

0 10 20 30 40 50 60 70 80 90 100

Flo

w (

mm

day

-1)

Flow Exceedance (%)

LCR3T LCR4T LCR5T Boone

0.001

0.01

0.1

1

10

100

0 10 20 30 40 50 60 70 80 90 100

Flo

w (

mm

day

-1)

Flow Exceedance (%)

LCR3T LCR4T LCR5T Boone

59% of NO3-N export

0.001

0.01

0.1

1

10

100

0 10 20 30 40 50 60 70 80 90 100

Flo

w (

mm

day

-1)

Flow Exceedance (%)

LCR3T LCR4T LCR5T Boone

85% of NO3-N export

0.001

0.01

0.1

1

10

100

0 10 20 30 40 50 60 70 80 90 100

Flo

w (

mm

day

-1)

Flow Exceedance (%)

LCR3T LCR4T LCR5T Boone

98% of NO3-N export

Implications for Downstream Water Bodies• Headwater areas, including drainage districts, are the

source of water for downstream areas

Nitrate concentrations

decrease downstream in a

predictable manner

What does this upstream-downstream relation mean?

Contributions from

headwater areas

anchor the starting

concentrations

A relatively minor

reduction from the

source results in

major

improvements

downstream

This is good news

Nutrient Reduction Strategies for Tile Drained Area

Nitrogen Reduction Practices

Practice% Nitrate-N Reduction

[Average (Std. Dev.)]

Nitrogen

Management

Timing (Fall to spring) 6 (25)

Source (Liquid swine

compared to commercial)4 (11)

Nitrogen Application Rate Depends on starting point

Nitrification Inhibitor 9 (19)

Cover Crops (Rye) 31 (29)

Land Use

Perennial – Land retirement 85 (9)

Perennial – Energy Crops 72 (23)

Living Mulches 41 (16)

Extended Rotations 42 (12)

Edge-of-Field

Drainage Water Mgmt. 33 (32)*

Shallow Drainage 32 (15)*

Wetlands 52

Bioreactors 43 (21)

Buffers 91 (20)***Load reduction not concentration reduction**Concentration reduction of that water interacts with active zone below the buffer

Wetland Restoration

Typical reduction in TN = 50% TP = 20%

Bioreactors

Typical reduction in TN = 40-60%

Drainage Water Management

Typical reduction in TN = 20-30% TP = 0%

April 30, 1999

Cover Crops

Typical reduction in TN = 50% TP = 50%

Agroforestry Buffered Landscape

Typical reduction in TN = 40% TP = 45%

Tile drainage bypasses riparian buffers

Saturated Buffers

Typical reduction in TN = 40-60%

Conclusions

• Tile drainage has modified Iowa’s streamflow regime by increasing baseflow, changing recession and homogenizing hydrological characteristics

• Tile drainage decreased groundwater travel times in watersheds

• Tile drainage contributes to nutrient enrichment and loads, particularly with respect to nitrate

• There are nutrient reduction strategies available that can be used to reduce the impacts of tile drainage on water quality

• There can be not a lack of awareness of the role of tile drainage on Iowa’s rivers and streams