WSP08741

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1993
• Author: USGS
• Title: Reconnaissance of Water Quality of Lake Henry and Lake Meredith Reservior - Crowley County - Southeastern Colorado - April-October 1987
• Water Supply Pro - Doc Type: Report/Study

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Biological Constituents

The biological constituents analyzed in water
samples collected from Lalce Henry included phyto-
plankton and chlorophyll a. Phytoplankton popula-
tions are seldom homogeneous within a lalce; therefore.
the biological samples collected from Lalce Henry may
not be representative of the entire lalce.
The groups of phytoplankton that occurred in
Lake Henry during the sampling period were Bacillar-
iophyta (diatoms), Chlorophyta (green algae),
Chrysophyta (golden-brown algae), Cryptophyta
(cryptomonads). Cyanophyta (blue-green algae). and
Euglenophyta (euglenoids) (table ]7, "Supplemental
Data" section at the back of this report). The densities
of phytoplankton collected near the lake surface at site
HEW2 varied from 33,000 cells/mL on June 29 to
930,000 cells/mL on August] 9 (fig. 7). On each sam-
pling date. blue-green algae comprised the greatest per-
centage of the phytoplankton density.
Of the total phytoplankton density on May I, dia-
toms comprised about 0.4 percent; green algae com-
prised about 12 percent (Chlorella and Coccomyxa
minor were the dominant algae); and cryptomonads
comprised about 19 percent (Rhodomonas minura was
the only species detected). Cryptomonads are consid-
ered to be common winter algae (Wetzel, 1975), which
might account for the larger concentration of this group
analyzed on May I. On May I, blue:green algae com-
prised about 69 percent of the total !'hytoplankton den-
sity. Of this group, the most dominant genera were
Aphanothece, Chroococcus, Microcyst/s, and SynecllO-
coccus.
The total phytoplankton density of 33,000
cells/mL on June 29 was less than analyzed on May I.
According to Wetzel (]975). phytoplankton densities
commonly increase in the spring and then decrease to a
brief summer minimum. Of the total phytoplankton
density on June 29, diatoms comprised about 10 per-
cent (Melosira granulata was the dominant species);
green algae comprised about] I percent (Coccomyxa
minor was the dominant species); blue-green algae
comprised about 79 percent; and cryptomonads and
golden-brown algae comprised the remaining percent-
age.
A substantial increase in phytoplankton densities
occurred between June 29 and August 19. On
August 19. the total cell count was 930,000 cells/mL,
and about 98 percent were blue-green algae. In more
eutrophic lalces. the brief summer minimum often is
followed by a late summer profusion of blue-green
algae that lasts into autumn (Wetzel, 1975). Of the
blue-green algae collected in August, about 91 percent
were of the genus M/crocyst/s. This algae commonly

occurs in hard water and tends to develop in nutrient-
rich, eutrophic lalces during the warmest summer
months (Hutchinson. 1967; Greeson, 1982). Various
water-quality problems are associated with an abun-
dant M/crocystis population. This algae, where present
in large masses, is capable of producing a foul odor and
taste and may cause the death offish in heavily infested
lalces (Palmer, 1977; Greeson, 1982).

The phytoplankton population remained large on
October 6 with a total density of 900.000 cells/mL.
Blue-green algae comprised about 98 percent of the
total phytoplankton density. The genus Microcystis
was absent from this sample, and the genus Aphanoth-
ece was the dominant algae and comprised about
95 percent of the blue-green algae. Aphanothece is
common to western ]alces and is very small in size.
This algae is not known to cause water-quality prob-
lems such as taste and odor and. as such, is not an indi-
cator of water quality. Little is known about this algae
because of its small size (Chadwick and Associates.
oral commun., 1988). Decomposition of the large
phytoplankton population present in October poten-
tially could deplete dissolved oxygen.

During the sampling period, chlorophyll a con-
centrations measured for site HEW2 at Lake Henry
ranged from 1.6 to 26.1 JlglL and averaged about
10 Jlg/L. The smallest concentrations were measured
on May I, and the largest concentrations were mea-
sured on October 6 (table 6). Concentrations of chlo-
rophyll a are used to determine trophic status.

Table 6. Concentrations of chlorophyll a for site HEW2 at
Lake Henry

(Jlg/L, micrograms per liter)

Sampling Sampling depth Chtorophyll a
data, 1987 (Ieet) (~gIL)
May 1 2.0 1.6
8.0 4.2
June 29 2.0 8.2
8.0 7.1
August 19 2.0 6.2
4.0 8.0
October 6 2.0 26.1
5.0 19.0

WATER-QUALtTY CHARACTERtSTtCS OF LAKE HENRY AND COMPARISON TO WATER.QUALlTY STANDARDS 17