Nonpoint-source pollutant discharges of the three major tributaries to Reelfoot Lake, west Tennessee, October 1987-September 1989

An investigation of the concentration and
loads of nitrogen, phosphorus, and suspended
sediment in storm runoff to Reelfoot Lake, in
western Tennessee, was conducted from October
1987 through September 1989. Concentrations of
selected herbicides also were defined. Reelfoot
Lake, with a sur$ace area of about 15,500 acres,
is the largest natural lake in Tennessee and an
important recreation and fisheries resource.
Previous studies showed that the lake is
hypereutrophic, a condition caused by high
concentrations of nutrients in water and sediments
discharged from the three principal tributaries
(South Reelfoot Creek, North Reelfoot Creek, and
Running Slough) to the lake. Pesticides, including
herbicides, have been detected in the lake?s
bottom sediments.
Storm runoff contributed about 87percent of
the total water discharge of the three main
tributaries to Reelfoot Lake. South Reelfoot
Creek contributed about 4.7 tons per acre per year
of suspended sediment, while North Reelfoot
Creek contributed about 1.9 tons per acre per
year. Running Slough contributed only about
0.31 ton per acre per year of suspended sediment.
Most of the suspended sediment was transported
by storm runoff between October and March.
About 80 percent of the annual streamflow of the
three tributaries occurs during these months.
The North Reelfoot Creek basin contributed
8.2 pounds per acre per year of total nitrogen and
2.4 pounds per acre per year of total phosphorus.
South Reelfoot Creek basin contributed about 6.5
and 1.3 pounds per acre per year of total nitrogen
and phosphorus, respectively, while Running
Slough basin contributions were 3.4 and
0.86 pounds per acre per year, respectively. The
differences in nutrient yields appear to result from
more row-crop agriculture and the relatively steeply
sloping agricultural land in the North Reelfoot
Creek basin. Ninety-one percent of the total
nitrogen load and 95 percent of the total
phosphorus load in the three streams was
transported by storm runof/ Significant diflerences
in the mean concentrations of nutrients in
runoff were defined between the active agricultural
months (April through September) and the
inactive months (October through March).
Storm-runofS samples were analyzed for
II selected triazine herbicides. Alachlor and
atrazine were the most commonly detected
herbicides. Thirty-two percent of the samples
contained detectable levels of alachlor and
93 percent of the samples contained detectable
levels of atrazine. Ninety percent of the samples
collected during the active agricultural months contained detectable leveki of alachlor and all
29 samples contained detectable levels of atrazine.
Sixteen samples exceeded lifetime health-advisory
levels for atrazine in drinking water (3 micrograms
per liter); two samples collected from the April IS,
1988, storm at North Reelfoot Creek and South
Reelfoot Creek contained 42 and 57 micrograms
per liter of atrazine, respectively. Concentrations
of the other nine triazine herbicides were generally
less than the level of detection (0.1 microgram per
liter).