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<br />0060
<br />
<br />Biological Constituents
<br />
<br />"
<br />
<br />The biological constituents analyzed in water
<br />S'mples collected from Lake Meredith included phy-
<br />toplankton and chlorophyll a. Phytoplankton popula-
<br />tions are seldom homogeneous within a lake; therefore,
<br />the biological samples collecled from Lake Meredith
<br />may not be representative of the entire lake.
<br />The groups of phytoplankton that occurred in
<br />Lake Meredith during the sampling period were Bacil-
<br />lariophyta (diatoms), Chlorophyta (green algae),
<br />Chrysophyta (golden-brown algae), Cryptophyta
<br />(cryptomonads), Cyanophyta (blue-green algae),
<br />Euglenophyta (euglenoids), and Pyrrhophyta
<br />(dinonagellates) (table 22. "Supplemental Data" sec-
<br />tion at the back of this report). The densities of phyto-
<br />plankton collected near the surface at site M2B ranged
<br />from 58.000 cells/mL on May I to 3,900,000 cells/mL
<br />on October 6 (fig. II). On each sampling date, blue-
<br />green algae comprised the largest percentage of the
<br />phytoplankton density.
<br />Of the total phytoplankton density on May I, dia-
<br />toms comprised about 7.5 percent, and Cyclotella stel-
<br />Iigera comprised about 94 percent of this group; green
<br />algae comprised about 24 percent; and blue-green
<br />algae comprised about 65 percent, and Aphanolhece
<br />and Aphoflocapsa comprised aboul 75 percent of this
<br />group. The remainder of the total phytoplankton den-
<br />sity consisted of golden-brown algae. euglenoids,
<br />dinoRagellates, and cryptomonads.
<br />The phytoplankton density on June 30 increased
<br />to 2,100,000 cells/mL of which about 99 percent were
<br />blue-green algae. Microcystis iflcerta comprised about
<br />87 percent of the blue-green algae. This species is
<br />common in hard water and tends to develop in nutrient-
<br />rich, eutrophic lakes during the warmest summer
<br />months (Hutchinson. 1967; Greeson, 1982). Various
<br />water-quality problems are associated with an abun-
<br />dant Microcystis population. This algae, where present
<br />in large masses, is capable of producing a foul odor and
<br />taste and may cause the death of fish in heavily infested
<br />lakes (Palmer, 1977; Greeson, 1982). The remainder of
<br />the phytoplanklon consisted of diatoms. green algae,
<br />and euglenoids.
<br />On August 20, the phytoplankton density was
<br />2,400,000 cells ImL. Green algae comprised about
<br />2.5 percent of the total, and blue-green algae comprised
<br />more than 96 percent of the total. The remainder of the
<br />phytoplankton were diatoms, euglenoids. and crypto-
<br />monads.
<br />The largest phytoplankton density of 3,900,000
<br />cells/mL was analyzed for October 6. Green algae
<br />comprised about 1.3 percent of the lotal, and blue-
<br />green algae comprised more than 98 percent of the
<br />total. The remainder of the phytoplankton population
<br />consisted of diatoms, euglenoids, and cryptomonads.
<br />
<br />During the sampling period, concentrations of
<br />chlorophyll a measured in Lake Meredith ranged from
<br />o to 37.8 ~g/L and averaged about 11.7 ~gIL. The
<br />smallest concentrations were measured on May I. and
<br />the largesl concentralions were measured on October 6
<br />(table 13).
<br />
<br />Table 13. Concentrations of chlorophyll a for sites M2B.
<br />M 1 B, and M4B at Lake Meredith
<br />
<br />[1lg!L. micrograms per liter}
<br />
<br />Sampling
<br />site
<br />(1Ig.3)
<br />M2B
<br />
<br />Sampling
<br />deplh
<br />(Ieel)
<br />2
<br />to
<br />2
<br />II
<br />2
<br />6
<br />2
<br />7
<br />2
<br />2
<br />12
<br />2
<br />8
<br />2
<br />2
<br />8
<br />2
<br />4
<br />
<br />4.0
<br />20.6
<br />7.4
<br />8.0
<br />7.3
<br />7.5
<br />37.8
<br />18.6
<br />2.5
<br />5.5
<br />7.6
<br />16.9
<br />6.2
<br />0.0
<br />8.3
<br />8.8
<br />21.0
<br />23.0
<br />
<br />Sampling
<br />date.
<br />1987
<br />
<br />May I
<br />
<br />Chlorophyll 8
<br />(~gIL)
<br />
<br />June 30
<br />
<br />August 20
<br />
<br />October 6
<br />
<br />MIB
<br />
<br />May 1
<br />June 30
<br />
<br />August 20
<br />
<br />M4B
<br />
<br />May I
<br />June 30
<br />
<br />August 21
<br />
<br />Trophic Status
<br />
<br />In calculating Carlson's trophic-state index (TSI)
<br />for Lake Meredith, Secchi-disk depth (SO), average sur-
<br />face concentrations of total phosphorus (TP), and aver-
<br />age surface concentrations of chlorophyll a (ChI) were
<br />used from samples collected at sites M2B, M I B, and
<br />M4B on June 30 and August 20 and 2 I. The average TSI
<br />values were greater than 51 for each trophic variable
<br />(table 14). which is considered by Carlson (1979) to be
<br />eutrophic.
<br />In applying the trophic variables to the fixed-
<br />boundary system. data were used from samples collected
<br />at sites M2B, M I B, and M4B on May], June 30, and
<br />August 20-21, and at sile M2B on Oclober 6 (table 7).
<br />The resulting trophic classification agrees closely with
<br />the calculations for the trophic-state index. The trophic
<br />classification, using the fixed-boundary system, indicates
<br />
<br />WATER-QUALITY CHARACTERISTICS OF LAKE MEREDITH AND COMPARISON TO WATER.QUALlTY STANDARDS 27
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