1. Impact of agricultural stream restoration on
hydrology and biogeochemistry
Sara McMillan, Gavin Downs, Maria Laura Ortiz de Zarate
Purdue University
Philippe Vidon, Molly Welsh
SUNY-ESF

2. Pristine
Impaired
Restored?
Rationale & project goals
 Restoration goals AND practices focus on stream channel stability and reduced
sediment transport
 Channel construction, engineered structures designed to achieve stability, grade
control and bank stabilization.
- How do physical changes influence near-stream hydrology?
- What is the effect of restoration on water quality (NO3, NH4, PO4) and GHG
emissions (CH4, N2O, CO2) in streams & riparian zones?
- Drivers of N, P and C cycling in the stream-riparian system?

3. Stream-Floodplain-Riparian System
Riparian buffer function:
 Transform and remove nutrients from adjacent uplands
Floodplain function:
 Overbank flow + enhanced hyporheic exchange attenuates peak flow and
retains/transforms nutrients & sediment
Stream function:
 Hyporheic flow & retention in deep pools retains and transforms nutrients
OC input
(leaves)
Nutrient
transport
Nutrient,
sediment input
during floods
NO3
- transport
Nitrification,
root uptake
DOC
transport
Debris dam
Cross vane
OM accum
Lateral hyporheic
flow
Denitrification
OM accum
Flow

4. Grassy Creek-Horne
Creek Watershed
Unrestored – Forested Buffer
Drainage area = 5 km2
Middle Fisher River
Watershed
1
2
3
Agriculture
Herbaceous
Forested
Open Space
Restored
Drainage area = 1.5 km2
Unrestored – Mixed Buffer
Drainage area = 4.5 km2
Study Sites

5. Study Sites
Site ID Stream Riparian area
Restored (R) Cross vane structures (boulders), riffle/pools,
floodplain regrading
27 m; herbaceous
Unrestored (UR) Channelized drainage ditch 4 m; herbaceous
Unrestored + mixed buffer
(UR-MB)
Incised channel but high complexity and
meanders; mixed forest & herbaceous buffer
17 m; forested
Unrestored + forest buffer
(UR-FB)
Floodplain connection on inner meander; high
bed complexity; incised & widened
20+ m; forested
Restored (R) Unrestored (UR)
Unrestored + mixed
buffer (UR-MB)
Unrestored + forest
buffer (UR-FB)

6. Approach & Methods
1) Riparian & Floodplain
a. Seasonal & event-based hydrology, water quality and
GHG fluxes
2) Stream & Hyporheic Zone:
a. Seasonal hydrology, water quality
b. Potential denitrification rates
c. Reach scale nutrient retention
3) Stream-Floodplain-Riparian connectivity
a. High temporal resolution: water table, stream height
& soil moisture

7. Riffle
A2
B1
C
D1
E
F
G2
H2
I1
1
2
3
4
5
7
8
6
A1Riffle
B2
D2
G1H1
I2
Piez. Color Code
Red = Well (W)
Orange = Deep (D)
= Mid (M)
Green = Shallow (S)
2” well
RunRiffleRun
Run4
J2/5
J1/6K/7
Pool8
Run
910
Example of monitoring framework – Restored site
Legend
In-stream
piezometer
Staff Gage
Rocks
Piezometer nest
Static chamber
Soil Moisture
Sensors/ Silicone
chambers

8. STREAM-FLOODPLAIN-RIPARIAN CONNECTIVITY

9. Greenhouse Gases: Riparian Function
 Highly variable; both
nitrification & denitrification
contribute to total flux
 U-Forest is net sink/zero
 Restored = lowest rate likely
because low soil OM +
compacted riparian zones
 Highest rates in summer/fall
(warm temperatures)
 U-Forested site is a sink
 Restored site = source. No
pattern with hillslope position
or restoration feature.
-1.5
-1
-0.5
0
0.5
1
1.5
2
N2OmgN/m2/d
R U U-FB
-20
-10
0
10
20
30
40
CH4mgC/m2/d
NSNSNS
-2
-1
0
1
2
3
4
CO2gC/m2/d
N
D
N
D
N
D
N
D
N
D
N
D

10. Storm events – Restored site
-1
0
1
2
3
4
5
N2O(mg
N/m2/day)
PRE 24h 72h
-1
0
1
2
3
4
5
6
7
8
CO2(gC/m2/day)
PRE 24h 72h
-60
-40
-20
0
20
40
60
CH4(mgC/m2/day)
PRE 24h 72h
 N2O – Uplands source post event
 CH4 – Near stream shifts from
sink to source post event.
 CO2 – No change

11. Hillslope position affects riparian-stream denitrification
 Denitrification in
riparian zones >
stream sediments
 Near-stream zones =
higher rates in
restored sites
 Highest rates
associated with
higher soil moisture &
organic carbon

12. R UR UR-
MB
UR-
FB
a
Pool Riffle Run Point bar
DEA(ngN/gDM/hr)
0
50
100
150
200
250
300
350
400
450
sandy
clay
loamy
sand
fine sand sand coarse
sand
DEA(ngN/gDM/h)
DEA by texture (in-stream locations)
Geomorphology & sediment drive instream denitrification
 Highest rates associated with fine textured sediments
 Pools high in unrestored sites
 Riffles high/variable in all sites
10
0
20
0
0

13. Sw (m) 324
Vf (mm min-1) 0.95
U (mg m-2 h-1) 14.5
Residuals
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
29
32
35
38
45
55
55.7
59.5
67.5
75.5
79
81
99.5
102
105
107
116
119.5
120.4
124
Riffles/shallow runs
Deep pools
- Sink
+ Source
Reach scale retention: Restored stream

14. Sw (m) 151
Vf (mm min-1) 2.75
U (mg m-2 h-1) 138
-0.60
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
11 15 24 28 35 41 42 45 50 65.4 66 68.4 79
Reach scale retention: U-Forested Riparian
- Sink
+ Source
Residuals

15. Conclusions, challenges and opportunities
 Consider the entire stream-riparian
system for restoration design &
assessment of function
• Denitrification and GHG patterns varied with
landscape position
• Denitrification: Riparian >> stream
• Instream DEA & nutrient uptake depended
upon geomorphology.
 Construction process = disturbance
• Vegetation removal, stream/riparian
regrading, soil compaction.
• Reduced water quality function
• Failures are common = maintenance

16. Thanks! Questions?