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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5047

Water Quality of Eleven Lakes in Eastern and Southern Arkansas from August 2004 - July 2005

By B.G. Justus

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Abstract

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.


TABLE OF CONTENTS

Figures
  1. Map showing location of lakes sampled in Arkansas
  2. Graph showing dissolved-oxygen concentration, pH, and dissolved-oxygen saturation at 30-minute intervals in seven Arkansas lakes for a 48-hour period in August 2004
  3. Orthophosphorus concentrations at 11 lake sampling sites in Arkansas, August 2004 - July 2005
  4. Total phosphorus concentrations at 11 lake sampling sites in Arkansas, August 2004 - July 2005
  5. Total ammonia plus organic nitrogen concentrations at 11 lake sampling sites in Arkansas, August 2004 - July 2005
  6. Total nitrogen concentrations at 11 lake sampling sites in Arkansas, August 2004 - July 2005
  7. Chlorophyll a, pheophytin a, turbidity, and total suspended solids values at 11 lake sampling sites in Arkansas, August 2004 - July 2005
  8. Nonpurgeable organic carbon, volatile suspended solids, and biochemical oxygen demand values at 11 lake sampling sites in Arkansas, August 2004 - July 2005
  9. Graph showing secchi depth for eight Arkansas lakes sampled for nutrients from August 2004 - July 2005
  10. Graph showing median concentrations for six chloride, sulfate, and total dissolved solid samples collected at three lakes in southern Arkansas, August 2004 - July 2005
Tables
  1. Information for lakes sampled in Arkansas, August 2004 - July 2005
  2. Sampling or frequency schedule for 11 lakes sampled in Arkansas, August 2004 - July 2005
  3. U.S. Environmental Protection Agency methods used to analyze water-quality samples for the lake study in Arkansas, August 2004 - July 2005
  4. Minimum and maximum values for pH, dissolved-oxygen concentrations, and dissolved-oxygen percent saturation for two 24-hour periods at seven Arkansas lakes
  5. Laboratory results for constituents analyzed at 11 water-quality monitoring sites, August 2004 - July 2005
  6. Secchi disc depth for lakes sampled from August 2004 - July 2005
  7. Chloride, sulfate, and total dissolved solids at three lakes in southern Arkansas, August 2004 - July 2005


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