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Click image for a larger view.
Click here to view
the above map with cities overlaid.
to print/zoom in on the above map (PDF file).
map to the left illustrates the USGS and Lake Michigan Mass Balance
Study sampling stations in the watershed. In 1995, extensive sampling
was conducted around Lake Michigan. This included tributary and
atmospheric sampling utilized to calculate a mass balance of pollutants
affecting Lake Michigan. The St. Joseph River was identified as
tributary source of atrazine to Lake Michigan. The graph below
illustrates the concentrations measured at the mouth of the St.
Joseph River. The table below illustrates the concentrations and
daily loads measured at the USGS sampling stations. See the bottom
of this page for more atrazine information.
chart for a larger view.
is the most widely used herbicide in the U.S., primarily in corn production.
has a mild solubility and low Henry's Law constant, which makes it very
susceptible to leaching by runoff.
is applied in the field late April through May.
degradation is slow in the water (only 0.8% per year in Lake Michigan).
- Lake Michigan
LaMP 2000 listed atrazine, a possible carcinogen, as an "Emerging Pollutant".
- Lake Michigan
LaMP 2002 continues to put atrazine on its "Watch List".
- The Lake
Michigan Mass Balance (LMMB) study, lead by EPA in 1994-1995, estimated
that the St. Joseph River Watershed is the largest atrazine contributor
to Lake Michigan at 602 kg/yr. However, (1) this estimate needs to be
updated; (2) more monitoring data are needed to support the estimate
(only 11 data points at the mouth of the St. Joe were collected in 1995
for the estimate), and; (3) no sub-basin level estimates are available.
- The LMMB
study, when modeling atrazine for Lake Michigan, used a "removal rate"
(% of land application atrazine transported to the lake) approach to
estimate tributary contributions. These removal rates were obtained
from the literature were not calibrated in the St. Joe River Basin.
- In the
LMMB study, EPA also indicated that more analysis at the watershed level
- A USDA-ERS
research report pointed out that the most cost-effective strategy to
control atrazine leaching to surface and ground waters is to target
atrazine management restrictions and alternatives (including partial
atrazine ban, runoff control BMPs, and crop management, etc.) to meet
water quality standards. This strategy requires the identification of
those watersheds with atrazine water quality problems and hydrological
conditions best suited for these management restrictions and alternatives.
- The USGS,
with funding from the State of Michigan, is conducting a study to look
into the transport
of atrazine in groundwater .