environmental setting, water quality, and ecological indicators of

Stream habitat ratings using RBP habitat characterizations
were rated optimal to marginal for all ecological
data-collection sites; ratings for 16 sites
were rated optimal to suboptimal.
Generally, median bank erosion scores and median
measurements of bankfull and wetted channel
widths were greatest at all site groups with large
drainage areas.
Generally, the median bank stability index and pool
substrate characterization score were lowest at all
site groups with high agricultural intensity.
Median values were lowest for 17 water-quality
variables at group A sites and highest for 11 waterquality
variables at group B sites.
Possible explanations for the differences in water
quality among site groups include the differences in
general soil types and agricultural land use in these
basins.
Increased turbidity and concentrations of nutrients
and insecticides, which normally are associated
with agricultural activities, occurred at group C
sites.
Water clarity and the amount of open canopy differed
among CCA site groups.
Organisms tolerant of turbidity, organic enrichment,
and low dissolved-oxygen concentrations are common
in the study and dominated the aquatic invertebrate
community.
Aquatic invertebrate communities at large-basin
sites tended to vary along the dissolved-oxygen and
open-canopy gradient, whereas communities at
small-basin sites tended to vary along the instreamcover
and fipronil-concentration gradient.
Aquatic invertebrate communities were significantly
different in percentage of noninsects, abundance
aof midge taxa, abundance of feeding groups,
and number of tolerant organisms among intensity
and CCA site groups.
Diversity metrics were similar among study-design
site groups but significant differences in dominance
and diversity occurred among CCA site groups.
In this study, the maximum concentration of dissolved
fipronil was the only significant environmental
variable related to consistent decreases in
relative abundance for many species, notably
midges.
Relative abundances for many species decreased at
lower concentrations of the fipronil degradation
products (fipronil sulfone, fipronil sulfide, and desulfinylfipronil)
than of the fipronil parent compound.
44
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