U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5047
By B.G. Justus
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In 2002, the U.S. Environmental Protection Agency
Region VI (USEPA), determined that historic data and observations
indicated that nine lakes were in violation of either narrative
or numeric water-quality standards for Arkansas. Using a
weight of evidence approach, USEPA determined that the narrative
nutrient (nitrogen and phosphorus, for example) standard
was violated at six lakes--five lakes located in eastern Arkansas
in the Mississippi Alluvial Plain Ecoregion and one lake
located in southeastern Arkansas in the South Central Plains
Ecoregion. USEPA also determined that chloride standards
were violated at two lakes located in the South Central Plains
Ecoregion in south-central Arkansas, and that turbidity standards
were violated at one lake located on Crowleys Ridge in
northeastern Arkansas in the Mississippi Alluvial Plain Ecoregion.
USEPA added all nine lakes to the Arkansas 2002 Clean
Water Act section 303(d) list of impaired waterbodies.
This report documents methods used and describes the
results for a water-quality study at 11 lakes--the 9 lakes in eastern
and southern Arkansas that had been previously placed on
the 2002 Clean Water Act section 303(d) list, as well as 2 reference
lakes. The study was conducted by the U.S. Geological
Survey in cooperation with the USEPA. The scope of the
project included lake reconnaissance, selection of the 2 reference
lakes, a 48-hour dissolved-oxygen investigation, waterquality
sampling in the 11 lakes between August 2004 - July
2005, and a basic interpretation of the data.
At all seven lakes selected for the 48-hour dissolved-oxygen
investigation, except Bear Creek Lake, dissolved-oxygen
concentrations declined below the State standard of 5 milligrams
per liter at some time in the 48-hour monitoring period.
Dissolved-oxygen concentrations (and, to a lesser extent, pH)
demonstrate large diurnal fluctuations at five of the lakes -- First
Old River, Grand, Horseshoe, Mallard, and Old Town Lakes.
Dissolved-oxygen concentrations were less than 1.5 milligrams
per liter at Mallard Lake and Grand Lake for short periods near
daybreak. The State pH standard of "9" was exceeded at all
lakes except Stave Lake (the nutrient reference lake).
Highest concentrations for most nutrients and nutrient
response variables were measured at Old Town Lake followed
by First Old River, Grand, and Mallard Lakes. Observations
made as samples were collected may provide some insight for
potential sources of nutrients (aside from row crop agriculture)
at three of the four lakes. Cattle usually were grazing along the
banks of First Old River Lake and Grand Lake. A small community
is located along the edge of Old Town Lake, and given
the age of many of the structures, it is possible that septic systems
are outdated and untreated waste may be entering the lake.
Aside from ammonia nitrogen concentrations at Bear
Creek Lake, concentrations of both nutrients and nutrient
response variables generally were lowest at Bear Creek, Horseshoe,
and Upper White Oak Lakes, and were comparable to
concentrations at Stave Lake--the reference lake. Of all samples,
highest concentrations for ammonia nitrogen were
observed at Bear Creek Lake; however, decomposition of large
amounts of leaves deposited near where water-quality samples
were collected probably resulted in ammonia nitrogen being
cycled into the aquatic environment.
Turbidity results indicate that Lake Frierson is impaired by
clay turbidity. Highest median turbidity concentrations were
observed at Lake Frierson and values measured at the site were
never below the Arkansas Department of Environmental Quality
numeric criteria of 25 nephlometric turbidity units. Secchi
depth (an indication of light penetration) also was consistently
lower at Lake Frierson than at other lakes.
Concentrations of chloride, sulfate, and total dissolved solids
were similar at the two lakes listed as being impaired by
chlorides (Lake Calion and Lake June) and were not close to
exceeding State standards of 250, 250, and 500 milligrams per
liter, respectively. However, concentrations for chloride at Lake
Calion and Lake June were about six to nine times higher than
concentrations at Upper White Oak Lake (the chloride reference
lake), and concentrations of sulfate and total dissolved solids at
Lake Calion and Lake June were about two times higher than
concentrations at Upper White Oak Lake.
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