Impact of agricultural stream restoration on hydrology and

biogeochemistry

Sara McMillan, Gavin Downs, Maria Laura Ortiz de ZaratePurdue University

Philippe Vidon, Molly WelshSUNY-ESF

Pristine Impaire

d

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?

Stream-Floodplain-Riparian SystemRiparian buffer function: Transform and remove nutrients from adjacent uplandsFloodplain function: Overbank flow + enhanced hyporheic exchange attenuates peak flow and

retains/transforms nutrients & sedimentStream 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 accumLateral hyporheic

flow

Denitrification

OM accumFlow

Grassy Creek-Horne Creek Watershed

Unrestored – Forested BufferDrainage area = 5 km2

Middle Fisher River Watershed

1 2

3

Agriculture

HerbaceousForested

Open Space

RestoredDrainage area = 1.5 km2

Unrestored – Mixed BufferDrainage area = 4.5 km2

Study Sites

Study SitesSite ID Stream Riparian area

Restored (R) Cross vane structures (boulders), riffle/pools, floodplain regrading

27 m; herbaceous

Unrestored (UR) Channelized drainage ditch 4 m; herbaceousUnrestored + 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)

Approach & Methods1) Riparian & Floodplain

a. Seasonal & event-based hydrology, water quality and GHG fluxes

2) Stream & Hyporheic Zone:a. Seasonal hydrology, water qualityb. Potential denitrification ratesc. Reach scale nutrient retention

3) Stream-Floodplain-Riparian connectivity a. High temporal resolution: water table, stream

height & soil moisture

RiffleA2

B1C

D1

E

F

G2H2

I1

1

2

3

4

5

7

8

6

A1Riffle

B2D2

G1H1

I2

Piez. Color Code Red = Well (W) Orange = Deep (D) Yellow = Mid (M) Green = Shallow (S)

2” well

RunRiffleRunRun4

J2/5

J1/6K/7Pool8

Run

910

Example of monitoring framework – Restored site

LegendIn-stream piezometer

Staff Gage

Rocks

Piezometer nest

Static chamber

Soil Moisture Sensors/ Silicone chambers

STREAM-FLOODPLAIN-RIPARIAN CONNECTIVITY

What is the influence of restoration on trade-offs between nutrient removal and greenhouse gas

emissions?

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.

Spr 1

3 SuFa

ll 13Win

13Sp

r 14 Su

Fall 1

4Win

14Sp

r 15 Su

-1.5-1

-0.50

0.51

1.52

R U U-FB

N2O

mg

N/m

2/d

Spr 1

3 SuFa

ll 13 Wi

Spr 1

4 SuFa

ll 14 Wi

Spr 1

5 Su-20-10

010203040

CH4

mg

C/m

2/d

NSNSNS

Sp Su Fal Wi Sp Su Fa

l Wi Sp Su-2-101234

CO2

g C/

m2/

d

ND

ND

ND

ND

ND

ND

Storm events – Restored site

-0.50

0.51

1.52

2.53

N2O

(m

g N

/m2/

day)

PRE 24h 72h

00.5

11.5

22.5

33.5

4

CO2

(g C

/m

2/da

y)

PRE 24h 72h-60-40-20

0204060

CH4

(mg

C/m

2/da

y)

PRE 24h 72h

N2O – Uplands source post event

CH4 – Near stream shifts from sink to source post event.

CO2 – No change

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

R UR UR-MB

UR-FB

aPool Riffle Run Point

bar

DEA

(ng

N/g

DM/h

r)

sandy clay

loamy sand

fine sand

sand coarse sand

0

50

100

150

200

250

300

DEA

(ng

N/g

DM

/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

100

200

0

Sw (m) 324Vf (mm min-1) 0.95U (mg m-2 h-1) 14.5

Residuals

Riffles/shallow runs

Deep pools

- Sink

+ Source

Reach scale retention: Restored stream

Sw (m) 151Vf (mm min-1) 2.75U (mg m-2 h-1) 138

Reach scale retention: U-Forested Riparian

- Sink

+ Source

Residuals

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

Thanks! Questions?