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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