Regional Changes in Water QualityAssociated with Switchgrass Feedstock

Virginia H. Dale1, Richard Lowrance2,

Patrick Mulholland1, G. Philip Robertson3

Presented by Betsy Smith

1Center for Bioenergy Sustainability, Oak Ridge National Laboratory

2USDA-ARS Southeast Watershed Research Laboratory

3 W.K. Kellogg Biological Station, Michigan State University

Roadmap for Talk

• Bioenergy sustainability and ecosystem services

• Effects of switchgrass – On soils have been measured– On water quality have been

modeled

• Regional decision making for bioenergy

• Experiments in the agricultural landscape

Challenge of sustainability of feedstock production

Water quality?Wildlife?

Soil carbon?Erosion?

Runoff?

Environmental Indicators of Bioenergy Feedstock Sustainability

Greenhouse gas emissions

Soil quality

Water quality and quantity

Air quality

Biological diversity

Productivity

Cross-cutting issues: Land-use change,

Ecosystem services, GMOs

Ecosystem services from native perennial grasses

GREATER INFILTRATION,LESS EROSION FROM SURFACE FLOW

DEEP ROOTING SYSTEM BENEFITS

DECREASED WINDFLOW AND EVAPORATION

LOWER FERTILIZER APPLICATION THAN CORN

Ongoing switchgrass study at Milan, TN

• DOE/USDA Milan switchgrass study (3rd growing season, fertilizer applied once per year in spring)

• Soil nitrate leaching higher and more variable under fertilization

• Apparent fertilizer application threshold for N leaching of between 67 and 202 kgN/ha/y (60 and 180 lbs/acre/y)

Data from M. Mayes, ORNL, unpublished

A horizon

Fertillization rate (kgN/ha/y)

0 67 202

Soil

solu

tion

nitra

te (m

g/L)

0.01

0.1

1

10

100B horizon

0 67 2020.01

0.1

1

10

100

n=5n=4

n=9

n=10n=22

n=27

1936 2336 2486Abovegr prod (g/m2/y):

Comparison of corn (no-till), switchgrass, and woody crops (short-rotation sweetgum) in northern Alabama

• Experimental study of bioenergy feedstock crops in north Alabama (DOE Bioenergy program

• Annual fertilizer regimes:

- corn: 112-134 N, 67-100 P

- switchgrass: 67-150 N; 67-112 P

- sweetgum: 0-84 N; 0-112 P

• Results:

- Much lower nitrate and P losses for sweetgum than corn

- Lower nitrate losses for switchgrass only in last 2 years, P loss similar to corn

- High erosion losses for sweetgum w/o cover crop (fescue)

Source: Nyakatawa et al. 2006, Biomass and Bioenergy 30:655-664

Watershed Modeling: Effects of converting corn/soybean to switchgrass - Rathbun Lake watershed (Iowa) study

• SWAT applied to Rathbun Lake watershed, Iowa

• Agricultural lands (corn, soybean) with high erosion and/or leaching potential converted to switchgrass

• Locally developed management practice schedules used for all crops (fertilizer, atrazine)

• Results:- Water yield declined by ~10%- Sediment yield declined by 55%- P export reduced by 36% - N export reduced by 38%- Atrazine export reduced by 86%

15% of watershed (1450 km2) converted to switchgrass

Source: Neppel, J., Rathbun Lake Watershed Assessment and Water Quality Implications of Switchgrass Biomass Production, M.S. Thesis, Iowa State University

Watershed modeling impacts using SWAT: Comparison of corn, alfalfa-corn, switchgrass for Upper Midwest

• Modeling study to compare alternative biofuels crops for Upper Midwest (corn, alfalfa-corn rotation, switchgrass)

• Evaluated two crop yield scenarios: normal, high (higher fertilization rates)

• Included assessment of N leaching and erosion using Integrated Farm Systems Model

• Results:

- N leaching ~30 to 40% lower for switchgrass than corn (but lowest for alfalfa/corn) ; directly related to fertilizer application

- Large reduction in erosion with switchgrass (> 90%) , modest reduction with alfalfa-corn

N L

each

ing

(kgN

/h

0

5

10

15

20

Eros

ion

(kg/

ha)

0

500

1000

1500

2000

2500

Fertilizer application (kg N/ha):

190

0 - 43

112

253

0 - 74

168

corn

alfa

lfa/c

orn

switc

hgra

ss

corn

alfa

lfa/c

orn

switc

hgra

ss

Normal application

Source: Vadas et al. 2008, Bioenerg. Res.

Switchgrass could help mitigate climate change effects on erosion in agricultural areas

• Modeling study of climate change effects on switchgrass and traditional crops in Missouri-Iowa-Nebraska-Kansas region;

• NCAR-RegCM2 nested with CSIRO GCM, 560 ppm CO2 scenario; EPIC crop growth model for erosion

• Regional climate forecast: Higher temperature (3-8ºC), higher precipitation (mostly spring and summer) and runoff

• Erosion increases under corn (up to two-fold) but decreases under switchgrass (higher ET due to longer growing season and plant biomass)

Source: Brown et al. 2000, Agriculture, Ecosyst., & Environ. 78:31-47

Scale Dependent Issues• The pattern, type, and management

of bioenergy crops can affect downstream conditions – Negatively -- if crops that require large

amounts of fertilizer are expanded

– Positively -- if bioenergy crops that need little fertilizer are planted in large areas or as buffers (Dale et al. 2010).

• For example, Gulf Hypoxia – The amount of nutrient and sediment

transported to the Gulf is not simply a direct function of what is coming from point and nonpoint sources (including agriculture)

– Nutrients flux must consider what’s lost along the way as water moves through the drainage network (Alexander et al. 2000).

Multiple influences on hypoxia in the Gulf of Mexico

5

43

2

1

5

43

2

1

Experiments in the Agricultural Landscape:A Watershed Approach to Bioenergy

• A systems-based approach– Captures cause and effects– Includes feedbacks– Calculate implications– Quantifies sustainability over

space– Allows options to be considered

• Landscape design– Quantifies desired conditions for

biofuel feedstock– Integrates spatial aspects of

environmental & socioeconomic constraints

• Spatial optimization– Quantifies potential sustainability

of bioenergy options– Operates at multiple scales

Vonore Pilot-Scale Biorefinery

Developing Watershed Approaches to Bioenergy Sustainability

• Modeling– Parameterizing SWAT for perennial grasses – Spatial optimization

• Quantifies potential sustainability of bioenergy options

• Operates at multiple scales

• Empirical measures– Design approach to test soil, water quality,

and habitat-related indicators at a landscape scale at Vonore, TN, biorefinery

– Implementation of design to test soil, water quality, and habitat-related indicators at a landscape scale using Vonore, TN

– Work with others to test sustainability indicators at other field sites

Conclusions – Sustainability of bioenergy crops depends on water resource impacts (among other ecosystem services)

• Cellulosic biofuels feedstocks (particularly native perennials such as switchgrass) may present win/win scenario for water quality and other ecosystem services but depend on conditions of the lands converted.

• Erosion and sediment loss to streams/rivers can be reduced by conversion from corn to switchgrass -depending on cover crop, site preparation

• Nutrient exports (surface water, groundwater) depend on fertilizer application rates– For switchgrass fertilization rates > ~100-150

kg N/ha seem to result in significant N losses

Visit the CBES website at http://www.ornl.gov/sci/besd/cbes for more information.