Regional Changes in Water Quality Associated with Switchgrass Feedstock

Transcription

1 Regional Changes in Water Quality Associated with Switchgrass Feedstock Virginia H. Dale 1, Richard Lowrance 2, Patrick Mulholland 1, G. Philip Robertson 3 Presented by Betsy Smith 1 Center for Bioenergy Sustainability, Oak Ridge National Laboratory 2 USDA-ARS Southeast Watershed Research Laboratory 3 W.K. Kellogg Biological Station, Michigan State University

2 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

3 Challenge of sustainability of feedstock production Erosion? Soil carbon? Water quality? Runoff? Wildlife?

4 Environmental Indicators of Bioenergy Feedstock Sustainability Greenhouse gas emissions Productivity Soil quality Cross-cutting issues: Land-use change, Ecosystem services, GMOs Biological diversity Air quality Water quality and quantity

5 Ecosystem services from native perennial grasses DECREASED WINDFLOW AND EVAPORATION GREATER INFILTRATION, LESS EROSION FROM SURFACE FLOW LOWER FERTILIZER APPLICATION THAN CORN DEEP ROOTING SYSTEM BENEFITS

6 Ongoing switchgrass study at Milan, TN DOE/USDA Milan switchgrass study (3 rd 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) Soil solution nitrate (mg/l) A horizon n=9 n=4 n=5 Abovegr prod (g/m2/y): B horizon n=27 n=22 n= Fertillization rate (kgn/ha/y) Data from M. Mayes, ORNL, unpublished

7 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: N, P - switchgrass: N; P - sweetgum: 0-84 N; 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:

8 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 km 2 ) converted to switchgrass Source: Neppel, J., Rathbun Lake Watershed Assessment and Water Quality Implications of Switchgrass Biomass Production, M.S. Thesis, Iowa State University

9 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 Erosion (kg/ha) N Leaching (kgn/h Fertilizer application (kg N/ha): corn Normal application alfalfa/corn 112 switchgrass corn alfalfa/corn 168 switchgrass Source: Vadas et al. 2008, Bioenerg. Res.

10 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

11 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).

12 Multiple influences on hypoxia in the Gulf of Mexico

13 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

14 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

15 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 > ~ kg N/ha seem to result in significant N losses

16 Visit the CBES website at for more information.