Biomass - Energy Policy Analysis: A Conceptual Framework - page 163

species. Coarse woody material that could be removed from a forest for biomass energy provides
crucial wildlife habitat for birds and small mammals; snags, den trees, and large downed woody
material are important to the well-being of many wildlife species (UCS 2010). Fuels made from
biomass waste products or native perennials grown on land not currently used for or well suited to
food crops can be produced without harmful changes in land use. Some types of land should not
be used for biofuel production, especially forests high in stored carbon and rich in biodiversity.
Cutting down rain forest in Indonesia to create palm oil plantations for manufacture of biofuels
is one example of biomass cultivation reducing biodiversity.
Biofuels that use land more efficiently, such as those derived from agricultural, forest-product,
and municipal waste streams, are more beneficial than food-based biofuels from a land-use per-
spective. Bioenergy crops that improve land currently considered unsuitable for agriculture are
likely to be the most beneficial of all (UCS 2008). Cultivating switchgrass on marginal agricultural
lands in the United States for production of biofuels is one example of this.
Water Quality
When crop-based biofuels contribute to deforestation or other damaging land conversions, envi-
ronmental costs can be high, potentially producing a net increase in pollution (UCS 2008). Cul-
tivation of bioenergy crops may increase sediment yield, nitrogen, and total phosphorous losses
in runoff from agricultural land (Nyakatawa et al. 2006). Phosphorous is particularly important
because it is often the critical nutrient triggering algae blooms in downstream lakes and other
slow-moving waters.
Similarly, excessive removal of crop residues may adversely impact water quality by increasing
transport of sediment, nitrogen, and phosphorous to downstream water bodies. Crop residues are
essential to conserve soil and water and improve crop production. Crop residue mulch increases
water infiltration and reduces the amount of rainfall runoff. It filters pollutants from runoff and
increases soil organic matter, which is essential for adsorbing and retaining pollutants (Dreiling
2009). Leaving crop residue on the soil surface is the best and simplest way of reducing water and
wind erosion. Widespread crop residue removal for use as biofuels may accelerate soil erosion
and increase loss of sediments, nutrients, and pesticides in runoff water. Sediment and nutrients
leaching into runoff are the main culprits of nonpoint source pollution flowing into downstream
water bodies (Dreiling 2009). In some semiarid regions of the United States, not enough crop
residue is produced in most years to protect soil from water and wind erosion and maintain ad-
equate levels of organic matter in the soil. Crop residue mulch plays a beneficial role in plowed
and no-till soils in reducing runoff transport of nonpoint source pollutants. In some watersheds,
only a fraction of crop residue may be available for removal without negatively affecting water
quality (Dreiling 2009). Soil organic carbon is essential to increase the soil's ability to absorb and
filter nonpoint source pollutants and maintain productivity of the soil (Dreiling 2009). Increases in
soil carbon storage occur on sites planted to woody or herbaceous species for biomass production
(Tolbert et al. 2002). But removing crop residue after harvest reduces soil carbon, total nitrogen,
and phosphorous (Dreiling 2009).
Crop residues are essential to reduce sediment, soil organic carbon, and nutrient loss in runoff,
regardless of tillage system. Crop residue left on the soil surface protects soil against impacting
raindrops, helps maintain the integrity of soil aggregates, and improves rainwater infiltration. Only
about 25 percent of crop residue may be available for removal for biomass energy production from
no-till soils, and less from intensively tilled soils, without degradation (Dreiling 2009).