Denitrification in wetlands

Denitrification in wetlands an ecological perspective

with collaboration from Maria Hernandez, Dan Fink and Li Zhang

The Mississippi-Ohio-Missouri (MOM) River Basin

From Mitsch and Day, 2006

Hypoxia in the Gulf of Mexico

20,500 km2

courtesy of Nancy Rabalais

Hypoxia in the Gulf of Mexico

20,720 km2

courtesy of Nancy Rabalais

Nitrate-warning history for Columbus Ohio Date

part per million (as N)

Duration (Days)

June 18, 1981

11.3

11

June 22, 1982

14.1

19

May 8, 1985

11.5

10

Jan. 18, 1989

10.7

9

Jan. 31, 1990

10.7

10

July 19, 1990

11.5

8

April 7, 1992

10.2

10

April 24, 1992

11.5

19

July, 1 1992

10.3

13

July 1, 1994

13.9

11

June 18, 1998

15.3

7

June 13, 2000

12.4

23

May 23, 2006

12.1

9

The City of Columbus has warned residents about high nitrate Levels in drinking water 13 times since 1981. Source: City of Columbus, The Columbus

Dispatch

Restoring the Mississippi-Ohio-Missouri River Basin

Better Fertilizer Management

Created/Restored Wetlands Mitsch et al. (2001)

Restore Riparian Bottomlands

Nitrogen uptake in wetlands in MOM basin

Source: Mitsch et al., 2005

Nitrogen uptake in wetlands in MOM basin

Source: Mitsch et al., 2005

Source: Mitsch and Gosselink, 2007

Nitrogen studies at the 
 Olentangy River Wetland Research Park Research

Years

References

Nitrate retention by experimental wetlands

1994-2008 Mitsch et al. 1998, 2005a,b

Comparison with WWT wetland/ model

1995-1997 Spieles and Mitsch, 2000

Nitrate-nitrogen model from ORW and other 1994-2003 Mitsch et al., 2005 wetlands including Louisiana delta in Mississippi River Basin Agricultural runoff wetland in Ohio

1998-2000 Fink and Mitsch, 2004

N2O emissions/denitrification with pulsing

2003-2005 Hernandez and Mitsch, 2006, 2007

Nitrogen retention by created oxbow

2004-2006 Fink and Mitsch, 2007; Mitsch et al., 2009

N2O emissions/denitrification-relation to vegetation communities and gradients

2008-2009 in progress

Wilma H. Schiermeier Olentangy River Wetland Research Park

Experimental wetlands

Wilma H. Schiermeier Olentangy River Wetland Research Park

Nitrate-nitrogen in an Ohio river and Mississippi Delta

Source: Mitsch et al. 2005

Denitrification studies

Oxbow Pulsing Experiment

Oxbow Wet Season

Oxbow Dry Season

Pulse experiment in oxbow

Pulse experiment in oxbow

Pulse experiment in oxbow

Nitrate Phosphorus retention retention g N m-2 yr-1 g P m-2 yr-1 Riparian oxbow wetland Sustainable retention rates

15 8

4.5 2.9

Pulsing Steady-flow

10 – 40

0.5 – 5

Mitsch et al., 2000

Experimental wetlands pulse experiment at the ORWRP

Wetland 1 inflow = 43.6 m/yr Wetland 2 inflow = 42.5 m/yr

Wetland 1 inflow = 39.1 m/yr Wetland 2 inflow = 39.1 m/yr

deep

shallow

N2O flux (µg N m-2 h-1)

Denitrification rate (µg N m-2 h-1)

Denitrification, nitrous oxide emissions, and N20/N2 ratio 1600 1400 1200 1000 800 600 400 200 0

High marsh

a

Edge

DENITRIFICATION

a

ab

a

ab ab b

b c c c

SP 04*

SU 04

50

-10

0.3

a

a

a a SP 04*

0.15

a SU 04

WI 05

SP 05*

SU 05

AU 05

bc c

c a

a

ca

a a

a

AU 04

a

SP 05*

a

a

a

WI 05

ac

a SU 05

AU 05

N2O/N2 RATIO Low marsh

0.25 0.2

c c

N2O EMISSIONS

70

10

bc

c c c

AU 04

90

30

b

b

b

110

0.3

N2O /N2 ratio

Low masrh

a

high marsh

pulses

edge

steady flow

0.1 0.05

0.0 0

SP 04*

a

SU 04

AU 04

WI 05

SP 05*

SU 05

AU 05

Sp 04 Su 04 Au 04 Wi 05 Sp 05 Su 05 Au 05

2008 (January – October)

NO3-N Inflow, kg-N yr-1

TKN Inflow, kg-N yr-1

TN Inflow, kg-N yr-1

NO3-N TKN TN Decrease Outflow, Outflow, Outflow, thru kg-N yr-1 kg-N yr-1 kg-N yr-1 wetland, kg-N yr-1

N Denitrifi sequest cation, ration*, kg-N yr-1 -1 kg-N yr

2004 Pulsing Planted Wetland

993 270 1263 522 288 810 453 162 25

2004 Pulsing Colonizing Wetland

993 266 1259 573 357 930 329 166 27

2005 Steady Flow Planted Wetland

846 309 1155 451 206 657 498 162 17

2005 Steady Flow Colonizing Wetland

846 309 1155 405 212 617 538 166 23

Goal is to create 28,000 ha of riparian systems and wetlands in one watershed in Ohio Columbus

OHIO

Conclusions Reestablishing connections between rivers and floodplains provides many much needed values for a watershed, particularly water quality improvement, flood mitigation, carbon sequestration, and wildlife enhancement. Business as usual of civilly and mechanically engineering ourselves out of disasters and environmental problems has got to be combined with ecologically engineering ourselves into sustainability. Restoration of over 2 million ha of wetlands is needed in the MOM basin to reduce the nitrogen load to the Gulf of Mexico sufficiently to ensure a reduction in the size of the hypoxia.

Conclusions Agronomic techniques, by themselves, are neither politically feasible, nor ecologically sufficient in scale to cause a significant improvement in water quality in MOM. The benefits of wetland restoration in the MOM Basin itself, even totally ignoring the Gulf hypoxia, are sufficient reasons by themselves for this large-scale restoration. Ecological restoration and creation of wetlands in MOM solves 3 main resource problems: wetland/habitat loss; degradation of water quality; and disastrous flooding damages.

Conclusions Determining the future of the Mississippi River Basin is difficult at best, given conflicting predictions of energy biofuel production in the Midwest and the excessive costs of fertilizers that may prohibit continued unsustainable agribusiness. Large-scale riparian restoration projects are already beginning in the MOM basin. These projects need comprehensive monitoring to determine their strategic importance to restoring their adjacent rivers and the MOM basin. Those doing restoration and creation of wetlands need to remember that self-design (Mother Nature) is a key principle and time (Father Time) an absolute necessity.

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