Environmental Engineering Reference
In-Depth Information
Joaquin Valley watershed. Differences in loads reflect variability in crops, soils,
CPY use intensity, and irrigation methods across the Central Valley.
Selection of watershed scenarios
. Three geographical areas of the U.S. (southeast-
ern Georgia, northwestern Michigan, and central California) were selected for
detailed investigation. This selection was based on the parallel examination of den-
sity of use of CPY across the U.S.; the modeling study of the relative vulnerability
to CPY being found in runoff with respect to soil and weather variability across the
U.S.; the evaluation of use- patterns that provided the greatest estimated concentra-
tions under a standardized scenario; and the modeling study of the relative vulner-
ability of CPY to runoff in California, based on detailed product-use records.
Counties in southeastern Georgia that were selected for further investigation
included Mitchell, Baker, and Miller. This region was chosen because it was among
those areas that sustained the highest density of CPY use in the country, it had rela-
tively high runoff potential in the national vulnerability assessment, and had the
greatest predicted exposure concentrations in the sensitivity analysis of use prac-
tices (GA-pecans). The Dry Creek watershed in the Flint River basin of Miller
County (Fig.
10
) was selected from this region for detailed modeling because it has
a high density of labeled crops eligible for CPY applications in the region. This
watershed is a third-order tributary within the Flint River watershed and drains an
area of 12,322 ha. Dry creek is a predominately agricultural watershed, where 69%
of the watershed is in agricultural land use (Table
7
and Fig.
10
), and in which non-
hay/pasture crops account for about 70% of the agricultural production area. The
primary non-pasture crops (i.e., crops registered for CPY) include cotton (21.7%),
peanut (16.3%), corn (5.5%), and pecan (0.6%). Most of the row crops are grown
with supplemental irrigation from center pivot irrigation systems.
The Leelanau peninsula of Michigan was selected because of the high exposure
concentrations estimated for the MI-cherry scenario, and that this area has one of
the greatest densities of cherry orchards in the USA. The Cedar Creek watershed in
the Betsie-Platte River system in Leelanau County was chosen based on having a
density of labeled crops eligible for CPY applications in the region (Fig.
11
). The
watershed drains 7,077 ha into Lake Leelanau, which, in turn, drains directly into
Lake Michigan. Land-use within the watersheds is 35% in agricultural production
and 23% of the area in non-hay/pasture agriculture (Table
7
). The primary crops in
the watershed are hay (12.0%), cherries (11.1%), alfalfa (8.1%), and corn (2.7%)
Orestimba Creek in the San Joaquin River basin of California (Fig.
12
) was
selected because of the high density of use of CPY in the watershed, frequent detec-
tions of CPY in ambient monitoring programs (Domagalski and Munday
2003
;
Ensminger et al.
2011
; Zhang et al.
2012
), and because an existing model setup of
the watershed was available from the University of California (Luo et al.
2008
; Luo
and Zhang
2010
). The watershed drains 55,998 ha from the mountainous area in
the west, where brush and scrubland is predominant, into the agriculturally intensive
valley floor. Overall, agriculture accounts for 22% of the total watershed area with
the primary crops being walnuts, almonds, corn and alfalfa (Table
7
).
In the intensely cropped valley floor, agriculture accounts for over 80% of land use.
In the time period from 2000 to 2008, 11,658 kg of CPY were applied.
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