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Water-Quality, Phytoplankton, and Trophic-Status Characteristics of Big Base and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004

By B.G. Justus

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Abstract

Little Rock Air Force Base is the largest C-130 base in the Air Force and is the only C-130 training base in the Department of Defense. Little Rock Air Force Base is located in central Arkansas near the eastern edge of the Ouachita Mountains, near the Mississippi Alluvial Plain, and within the Arkansas Valley Ecoregion. Habitats include upland pine forests, upland deciduous forest, broad-leaved deciduous swamps, and two small freshwater lakes—Big Base Lake and Little Base Lake. Big Base and Little Base Lakes are used primarily for recreational fishing by base personnel and the civilian public. Under normal (rainfall) conditions, Big Base Lake has a surface area of approximately 39 acres while surface area of Little Base Lake is approximately 1 acre.

Little Rock Air Force Base personnel are responsible for managing the fishery in these two lakes and since 1999 have started a nutrient enhancement program that involves sporadically adding fertilizer to Big Base Lake. As a means of determining the relations between water quality and primary production, Little Rock Air Force Base personnel have a need for biological (phytoplankton density), chemical (dissolved-oxygen and nutrient concentrations), and physical (water temperature and light transparency) data. To address these monitoring needs, the U.S. Geological Survey in cooperation with Little Rock Air Force Base, conducted a study to collect and analyze biological, chemical, and physical data. The U.S. Geological Survey sampled water quality in Big Base Lake and Little Base Lake on nine occasions from July 2003 through June 2004. Because of the difference in size, two sampling sites were established on Big Base Lake, while only one site was established on Little Base Lake.

Lake profile data for Big Base Lake indicate that low dissolved- oxygen concentrations in the hypolimnion probably constrain most fish species to the upper 5-6 feet of depth during the summer stratification period. Dissolved-oxygen concentrations in Big Base Lake below a depth of 6 feet generally were less than 3 milligrams per liter for summer months that were sampled in 2003 and 2004.

Some evidence indicates that phosphorus was limiting primary production during the sampling period. Dissolved nitrogen constituents frequently were detected in water samples (indicating availability) but dissolved phosphorus constituents-orthophosphorus and dissolved phosphorus-were not detected in any samples collected at the two lakes. The absence of dissolved phosphorus constituents and presence of total phosphorus indicates that all phosphorus was bound to suspended material (sediment particles and living organisms). Nitrogen:phosphorus ratios on most sampling occasions tended to be slightly higher than 16:1, which can be interpreted as further indication that phosphorus could be limiting primary production to some extent.

An alkalinity of 20 milligrams per liter of calcium carbonate or higher is recommended to optimize nutrient availability and buffering capacity in recreational fishing lakes and ponds. Median values for water samples collected at the three sites ranged from 12-13 milligrams per liter of calcium carbonate. Alkalinities ranged from 9-60 milligrams per liter of calcium carbonate, but 13 of 17 samples collected at the deepest site had alkalinities less than 20 milligrams per liter of calcium carbonate.

Results of three trophic-state indices, and a general trophic classification, as well as abundant green algae and large growths of blue-green algae indicate that Big Base Lake may be eutrophic. Trophic-state index values calculated using total phosphorus, chlorophyll a, and Secchi disc measurements from both lakes generally exceeded criteria at which lakes are considered to be eutrophic. A second method of determining lake trophic status-the general trophic classification-categorized the three sampling sites as mesotrophic or eutrophic. Green algae were found to be in abundance throughout most of the study period with the lowest biovolume during April and May 2004. Many of the green algae, such as Ankistrodesmus, Cryptomonas, Cyclotella, and Crucigenia, that were identified are less than 20 microns making them an appropriate size zooplankton for grazing; however, the abundance of green algae also is evidence of eutrophy.

In addition to being of little use as a food source to filter feeding zooplankton, some blue-green algae such as Anabaena species identified in this study can produce algal toxins such as microcystin, a hepatotoxin that can cause serious illness to humans as well as other mammals. In some States, blue-green algal densities at Big and Little Base Lakes would trigger tests for algal toxins. Fertilization of the lakes could compound the problem of algal toxicity. Introducing a fertilizer with less nitrogen than phosphorus (10:43:0) to the lakes could result in lake water being nitrogen limited. Nitrogen-limited lake water could favor blue-green algae (such as Anabaena or Microcystis spp.) that have the ability to fix atmospheric nitrogen as a nutrient source.


TABLE OF CONTENTS

Figures
  1. Map showing location of water-quality sampling sites on Big Base Lake and Little Base Lake, Little Rock Air Force Base, Arkansas, 2003-2004
  2. Distribution of water temperature with depth and time at Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, July 2003-June 2004
  3. Distribution of dissolved-oxygen concentrations with depth and time at Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, July 2003-June 2004
  4. Distribution of four nitrogen constituents analyzed from water samples collected in the epilimnion and hypolimnion at Big Base Lake West, Little Rock Air Force Base, Arkansas, 2003-2004
  5. Distribution of four nitrogen constituents analyzed from water samples collected in the epilimnion at Big Base Lake East and Little Base Lake, Little Rock Air Force Base, Arkansas, 2003-2004
  6. Distribution of orthophosphorus and total phosphorus in water samples collected from Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
  7. Distribution of alkalinity in water samples collected from Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
  8. Distribution of chlorophyll a in water samples collected from Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
  9. Graph showing biovolume of phytoplankton collected from Big Base Lake West, Little Rock Air Force Base, Arkansas, 2003-2004
  10. Boxplot showing distribution of turbidity in water samples collected from Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
  11. Graph showing algal biovolume for four groups of algae in Big Base Lake, Little Rock Air Force Base, Arkansas, July 2003-June 2004
  12. Graph showing algal biovolume for four groups of algae in Little Base Lake, Little Rock Air Force Base, Arkansas, July 2003-June 2004
  13. Distribution of a trophic-state index using total phosphorus data for water samples collected from Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
  14. Distribution of a trophic-state index using chlorophyll a data for water samples collected from Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
  15. Distribution of a trophic-state index using Secchi-depth measurements at Big and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
TABLES
  1. Site information for three lake sites sampled at Little Rock Air Force Base, Arkansas, 2003-2004.
  2. Nitrogen:phosphorus ratios for four sampling sites on Big Base and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
  3. Synopsis of dominant algae found in a study of Big Base Lake and Little Base Lake, Little Rock Air Force Base, Arkansas, 2003-2004
  4. A comparison of algal (Anabaena spp.) density and total algal biovolume in Big Base Lake to density and biovolume criteria for protection against harmful algae
  5. Trophic-state indices based on total phosphorus, chlorophyll a, and Secchi-depth measurements for sampling sites on Big Base and Little Base Lakes, Little Rock Air Force Base, Arkansas, 2003-2004
  6. A comparison of a general trophic classification of lakes and reservoirs to total phosphorus, chlorophyll a, and Secchi-depth data collected on nine occasions at three lake sites on Big Base and Little Base Lakes, Little Rock Air Force Base, 2003-2004

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