Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
derived from the SCS/ARS/CES Pesticide Properties Database for Environmental Decision Making
(Wauchope et al. 1992).
Soil properties influence the fate of pesticides in the environment. The following six properties are
mostly likely to affect pesticide degradation and the potential for pesticides to move off-site by
leaching (vertical movement through the soil) or runoff (lateral movement across the soil surface).
• Permeability is the rate of water movement vertically through the soil. It is affected by soil
texture and structure. Coarse textured soils (e.g., high sand content) have a larger pore size and
they are generally more permeable than fine textured soils (i.e., high clay content). The more
permeable soils would have a greater potential for pesticides to move vertically down through the
soil profile. Soil permeability rates (inches/hour) are usually available in county soil survey
reports.
• Soil texture describes the relative percentage of sand, silt, and clay. In general, greater clay
content with smaller the pore size would lower the likelihood and rate water that would move
through the soil profile. Clay also serves to adsorb (bind) pesticides to soil particles. Soils with
high clay content would absorb more pesticide than soils with relatively low clay content. In
contrast, sandy soils with coarser texture and lower water holding capacity would have a greater
potential for water to leach through them.
• Soil structure describes soil aggregation. Soils with a well developed soil structure have looser,
more aggregated, structure that would be less likely to be compacted. Both characteristics would
allow for less restricted flow of water through the soil profile resulting in greater infiltration.
• Organic matter would be the single most important factor affecting pesticide adsorption in soils.
Many pesticides are adsorbed to organic matter which would reduce their rate of downward
movement through the soil profile. Also, soils high in organic matter would tend to hold more
water, which may make less water available for leaching.
• Soil moisture affects how fast water would move through the soil. If soils are already wet or
saturated before rainfall or irrigation, excess moisture would runoff rather than infiltrate into the
soil profile. Soil moisture also would influence microbial and chemical activity in soil, which
effects pesticide degradation.
• Soil pH would influence chemical reactions that occur in the soil which in turn determines
whether or not a pesticide will degrade, rate of degradation, and, in some instances, which
degradation products are produced.
Based upon the aforementioned properties, soils most vulnerable to groundwater contamination
would be sandy soils with low organic matter. In contrast, the least vulnerable soils would be welldrained
clayey soils with high organic matter. Consequently, pesticides with the lowest potential for
movement in conjunction with appropriate best management practices (see below) would be used in
an IPM framework to treat pests while minimizing effects to non-target biota and protecting
environmental quality.
Along with soil properties, the potential for a pesticide to affect water quality through run-off and
leaching would consider site-specific environmental and abiotic conditions including rainfall, water
table conditions, and topography (Huddleston 1996).
• Water is necessary to separate pesticides from soil. This can occur in two basic ways. Pesticides
that are soluble move easily with runoff water. Pesticide-laden soil particles can be dislodged
and transported from the application site in runoff. The concentration of pesticides in the surface
runoff would be greatest for the first runoff event following treatment. The rainfall intensity and
Appendix G. Integrated Pest Management G-33