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| Photo by Irene Miles |
On its millions of acres of farmland, Illinois grows enough corn and soybeans to produce more ethanol than any other state in the US. If Illinois farmers decided to grow perennial grasses for biofuel rather than corn and soybeans, though, how might the way Illinois uses water and fertilizer change? That’s what Andy VanLoocke and Carl Bernacchi wanted to know, and they won an IWRC Annual Small Grant to fund their search for an answer. At the end of their project, Andy and Carl told us about their findings, what the research could mean for Illinois water resources, and what Andy is doing with his new PhD.
A cellulosic biofuel
feedstock is a crop that is grown primarily to convert the cellulose, most of a
plant’s structural material, into a fuel like ethanol. This is in contrast to
the “grain or oil” being used to produce ethanol or biodiesel, because with
cellulosic feedstocks the energy source isn’t limited to the seed of the crop,
like with corn or soybean.
Would you please give
us a quick overview of the whole project, not just the IWRC-funded piece?
The overall goal of
this project was to come up with a quantitative way to assess large-scale land
use shifts across the Midwest that are associated with biofuel production. We
also looked at the impacts this could have on the critical aspects of our
agro-ecosystems, such as the cycling of carbon, water, and nutrients. Within
the context of the IWRC funding, we were particularly focused on ecosystem water
use, such as determining how producing cellulosic bioenergy crops would alter stream
flows and water quality of our rivers.
Would you talk about
the models you used a little bit: what is IBIS, how do you determine model
inputs, and how accurate are the results?
Because we are asking
questions on such a large scale, and with numerous hypothetical scenarios, we
had to use computer models to answer our research questions. To model the
production of the crops we chose an ecosystem model called Agro-IBIS, which
stands for the Integrated BIoSphere model – Agricultural version. We ran this
model in conjunction with a stream flow and nutrient transport model called
Terrestrial Hydrology Model with Biogeochemistry (THMB).
To conduct this
research, we fed the ecosystem model (Agro-IBIS) climate data including temperature
and precipitation. The model then simulated the uptake of carbon through
photosynthesis, the loss of water through transpiration and evaporation, and a
range of other outputs. We also input management information into Agro-IBIS,
such as crop type and fertilization rates that are used with the climate data
to determine how much carbon, nitrogen, and water are entering and leaving a
given location (typically the size of a county). The results of Agro-IBIS are
then given as inputs into THMB, which simulates the movement of water and
nitrogen runoff from each location, through the various rivers and streams of
the Mississippi River Basin, and eventually out to the Gulf of Mexico.
We compare the model
results to any available observations we can find to insure the model is
accurate. For the new cellulosic biofuel crops, information is limited, but we
have been able to compare the model predictions for key components of the
carbon, water, and nitrogen cycles for a few locations in Central Illinois. So
far the models do a pretty good job simulating what we have seen in the field. Given
the limited data, there are uncertainties when scaling from the well-measured
areas to the whole region. We can increase the confidence in the model over larger
spatial scales by modeling existing crops (corn, soy, and wheat), which we have
much more information on, and determine how well the modeled data and measured
data agree.
What were your major
findings?
The primary question
we were trying to address is: What impact would large-scale production of
cellulosic feedstock in the Midwest have on water quality and quantity in the
Mississippi River Basin? We know from observations that Miscanthus and
Switchgrass, the two major leading candidate cellulosic feedstocks and our
study focus, use more water than corn and soybean, but require less fertilizer
to achieve high yields. When we expanded the study with the computer models we
found that, as long as we kept production less than the current fraction levels
(i.e. ~40% of corn grain goes to ethanol each year), there was a minimal impact
on streamflow for most of the Mississippi River Basin. At the same time we saw
that we could significantly improve water quality if we followed these
production scenarios.
