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