Open Literature Review Summary

Chemical Name: Atrazine

CAS No: 1912-24-9

ECOTOX Record Number and Citation:

Herman, D., N:K7Kausnik, and-K:R~Soiomon. N8°6-:-Impactof atr:fzine on periphyton.-------

in freshwater enclosures and some ecological consequences. Can. J. Fish. Aquat. Sci.

43:1917-1925 (MRlD 47543502).

Purpose of Review:

Determine potential effects of atrazine on an aquatic community. Endpoints from this

study contribute to the weight-of-evidence regarding effects of atrazine on aquatic plant

communities and associated determination of a Level ofConcern (LaC).

Date of Review:

November 24, 2009

Purpose of Study:

This study examines the potential effects of atrazine to aquatic plants (periphyton) in

experimental lake enclosures (limnocorrals).

Summary of Study Findings:

Methods: The basic experimental design ofthis study is also reported in Hamilton, et al.

(1987), Hamilton, et al. (1988), and Hamilton, et al. (1989).

Six enclosures (limnocorrals) were constructed in Lake St. George, a 10.3-ha

mesotrophic lake in southern Ontario, Canada (two other articles headed by a co-author

are cited for details). The enclosures were 5 m x 5 m x 5 m deep, and made of a single

piece of yellow nylon-reinforced polyvinyl chloride (PVC), supported on the water

surface by floats and anchored firmly in the sediment on the bottom. Three limnocorrals

were used as controls and three were treated with atrazine.

The enclosure walls were lowered on May 5, 1983, and remained in place until July

1984. Periphyton substrates were colonized for 3 weeks before the first atrazine

treatment. Two atrazine treatments occurred, on June 1, 1983 and July 6, 1983 (Day 35).

Atrazine (80% active ingredient, manufacturer not provided) was applied to the water

1
surface using a backpack spray system to give a nominal concentration of 100 jlg/L with

each application. Complete mixing ofthe atrazine within the enclosures occurred within

24 hours. Atrazine concentrations measurements were carried out (described in a

separate paper). Due to lack of water exchange with the lake for nutrient renewal,

weekly nutrient additions were applied to the enclosures at a rate equivalent to 6.5 g

N/m2

/yr (as sodium nitrate) and 0.5 g P/m2/yr (as phosphoric acid).

------PeriphytOTcco+oni-zatiol1 :substrates-were made-of-6:-§-Gin-x-4-Gm-s~r-ips-6Hhe-same~P-VGu-------­

material used for the enclosures, with two strips attached to a holder using silicone glue.

A holder was made ofthree 2.5 cm x 10 cm microscope slides attached along their short

edge to a 20 cm segment of glass tubing using silicone glue. A sampling unit was created

by tying four such holders together with nylon string, spaced at 0.5, 1.5,2.5, and 3.5 m

depths. Twelve sampling units were placed in each enclosure, and one unit was

randomly selected and extracted on each sampling day. Sampling occurred on Days 1, 5,

14,24,34,37,42,54,68,96;137, and 329.

For periphyton sampling, one strip from a holder at each depth was immediately

preserved in Lugol's solution to be used to direct enumeration. Using a scalpel,

periphyton from the second strip was scraped into distilled water and mixing until

homogeneous in a Waring blender. Aliquots ofthe resulting suspension were analyzed

for chlorophyll and organic matter content.

To determine organic matter content, samples were filtered onto a preashed, preweighed

Whatman GFC (2.4-cm diameter) filter and dried at 70°C for about 24 hours, then

weighed, the ashed at 500°C for 1 hour and reweighed. The dry weight minus the ashed

weight gave the ash-free dry weight (AFDW), used as an estimate of organic matter. For'

chlorophyll analysis, the samples were filtered onto Whatman GFC filters and frozen

until extraction. Chlorophyll extraction followed the published methods ofMarker, et at.

(1980) and Arvola (1981), and spectrophotometric analysis of chlorophyll a with a

Bausch and Lomb Spectronic 88 used the equations and procedure given by Nusch

(1980) (see article for full citations; all are in peer-reviewedjoumals).

Periphyton algae enumeration followed the procedure of Lund, et at. (1958) (inverted

microscope technique). The homogenized suspension samples were subsampled and

allowed to settle for at least 12 hours in a 50 mL phytoplankton sedimentation chamber.

At least 300 cells were counted per sample. Filamentous algae had been broken into

short chains by the blending, and individual cells were counted in these. For the more

intact Cyanophyta filaments, number of cells was estimated using filament length and

average cell size. Length, width, and depth were measured on a random selection of 3-6

cells for each species, total species volume was calculated assumed a simple geometric

solid form ofthe cells, and fresh weight biomass was estimated from volume assuming a

cell density equivalent to the density of water.

2
,

..

Periphyton photosynthetic activity was measured in situ using 14C assimilation as an

estimate of net primary productivity. A microscope slide was attached on the edge ofa

lid for a 250 mL glass incubation bottle, perpendicular to the inside surface, using

silicone glue, and an injection port was drilled through the lid and sealed with silicone

glue. A 6.5 cm x 2.5 cm strip of PVC was sealed to the slide, using silicone glue, for

periphyton colonization, and each lid was attached to holder, as described previously.

Four holders were tied together for periphyton sampling at 0.5, 1.5,2.5, and 3.5 m

depths. 3 sets of holders were suspended in each enclosure on May 6 and allowed to

-----,c=oionize for 3Saays before the firs! productivity measurem-ent:-Be'(;cmse pro-ductivity

measurements were onerous, only one control and on treatment enclosure were sampled

over three 3-day productivity sampling periods, two in the first pulse and one after the

second.

For productivity samples,water samples from the enclosures at the appropriate depths

were taken using a Kemmerer sampler and dispensed into 250 mL incubation bottles.

Lids, with the attached periphyton substrate, were fitted to each bottle. The bottles were

suspended at the sampling depths for 30 minutes to stabilize their temperature before

being brought to the surface, injected with 74 kBq of 14C-Iabeled sodium bicarbonate

(Amersham, Oakville, Ontario), and then lowered again and incubated for 2 hours. All

incubations were carried out in the same controllimnocorral between 10:00 and 14:00.

After incubation, the periphyton was scraped from the PVC strip and filtered onto a

Millipore (45 /lm) filter, a drop of 0.5 N HCI was added to eliminate any retained

radiolabeled bicarbonate, and the filters were place in a scintillation bottle containing 3

mL of2-methoxyethanol and 12 mL of Aquasol-2 (New England Nuclear).

Radioactivity was measured in a Packard Tri-Carb 460C liquid scintillation system using

the sample channel ratio method to correct for quenching due to detritus or chlorophyll.

During one periphyton productivity measurement, phytoplankton samples from four

depths were incubated for 3 hours in 500 mL bottle at the same time as the periphyton,

after injecting 111 kBq of 14C-Iabeled sodium bicarbonate through a port in the lid. The

phytoplankton 14C assimilation was then measured as described for periphyton.

Light readings were taken with a Li-Cor spherical quantum sensor (Li-1935b) sensitive to

photosynthetically active radiation (-400-700 nm) and recorded on aLi-Cor (Li-51 OB)

data integrator. Carbon assimilation was calculated using methods described in the

manual of Vollenweider (1969).

Water quality measurements were taken weekly. Temperature and dissolved oxygen

profiles were sampled using a YSI model 51B (Yellow Springs Instrument Co.) dissolved

oxygen meter. Water samples were collected using a depth integrated sampler and

analyzed for Kjeldahl nitrogen, combined nitrate-nitrite nitrogen .(N03-N02-N), total

phosphorus, dissolved inorganic carbon (DIC), and phytoplankton chlorophyll a using the

3

- -----
standard methods of Environment Canada, 1979. (Secchi depth measurement results ar.e

described in Table 1, but the methods are not introduced.)

Analysis of variance (ANOVA) with pooled variance was used to analyze AFDW,

chlorophyll, and carbon assimilation rates on each sampling day or measurement period,

with sampling depth considered as a separate factor. For algal biomass, the means and

standard errors were calculated for each sampling depth.

Results: The results presented in the article are related to the following articles:

Hamilton, et al. (1987), Hamilton, et al. (1988), and Hamilton, et al. (1989). The atrazine

concentrations are also presented, in the mean, in Hamilton, et al. (1989). Similar water

quality measures are provided in Hamilton, et al. (1987) and are summarized differently

(and more completely) in Hamilton, et al. (1989). Many ofthe periphyton measures

appear similar to those of Hamilton, et al. (1987); however, the methods described in the

1987 article are different and appear to be separate (later in the season) periphyton

investigations within the same enclosures.

Atrazine measurements in the 3 treatment enclosures are shown in Figure 1. During the

first pulse, concentrations ranged from 80-140 jJg/L, and after the second pulse the

concentration increased 20-30% in all enclosures rather than doubling. Water quality

measures showed no significant differences between treatments and controls during the

first pulse, but throughout the second pulse (before the next spring), treatments had

significantly (no p-value) lower oxygen concentrations at 0.5 and 3.5 m depths, and

significantly (no p-value) greater Secchi depth, DIC, and N03-N02-N. By the following

spring (Day 329), all parameters had recovered with the exception ofN03-N02-N, which

remained increased in the treatment enclosures. See Table 1.

AFDW was greater in the controls than in the treatment enclosures, particularly after the

second pulse (see Figure 2). Differences were significant (no p-value) at 0.5 m depth on

Day 34, and at 0.5 and 1.5 m depths on most subsequent sampling days.

Chlorophyll values showed no significant differences between treatments and controls

until 19 days after the second atrazine application (Day 54), and after that, chlorophyll

levels were consistently lower in the treatment enclosures, though not all differences

were significant (no p-value). See Figure 3. Periphyton organic matter decreased with

the sampling depth, but there was no effect on depth on chlorophyll.

Algal groups in the periphyton' were the Cyanophyta (blue-green), Chlorophyta (green),

and the Bacillariophyceae (diatoms). On the first sampling day, the p<mnate

Bacillariophyceae dominated in most control and treatment enclosures (Table 2).

Dominant species were Fragilaria crotonensis and Synedra spp., with others also

common including Achnanthes minutissima, Tabelariafenestrate, Cymbella cistula,

4
Gomphonema angustatum, G. truncatum, and Navicula radiosa. After the spring bloom,

the BaciIIariophyceae in both control and treatment enclosures were dominated by

Achnanthes minutissima and Gomphonema angustatum. For the rest ofthe summer, the

Chlorophyta group dominated total algal biomass and cell numbers in both control and

treatment communities. Chlorophyta in the control enclosures were dominated by

filamentous species, primarily Oedogonium sp. and Bulbochaete sp. by biomass, and in

the atrazine enclosures, Coleochaete sp. was dominant. See Figure 4. The most drastic

impact of atrazine on the algal groups was on Cyanophyta. In the controls, Oscillatoria

------s"'"'p".....-=a=n-:>a umctentille<:Cffagmentsoominateci, witilToiypotftrlX sp. increasing in numiJeroy-------

September. In the treatment enclosures, Cyanophyta almost completely disappeared

during the first pulse (Figure 5), despite no apparent impact on Chlorophyta or

BaciIIariophyceae, which only decreased relative to controls on Day 42 and 96

(respectively), and then not at all depths. Cyanophyta in the treatment enclosures

remained absent for the remainder ofthe experiment. The following spring, (Day 329),

Bacillariophyceae and Cyanophyta had increased in relative abundance in the control

enclosures, while in the atrazine treated enclosures Chlorophyta dominated biomass and

Bacillariophyceae dominated total cell numbers. Overall biomass in the treatments did

not recover to become similar to control levels.

Carbon assimilation measurements (Figure 6) showed no significant differences due to

treatment in the first pulse, but significantly (no p-value) lower rates were found during

the second pulse at 1.5 and 2.5 m. 0.5 m measurements during this time were not

possible due to loss ofthe PVC strips from Days 47-49.

Periphyton and plankton chlorophyll and productivity measurements were compared by

expressing each on a per-enclosure basis (multiplying the mean value ofthe four

sampling depths by the total wall surface area for the periphyton, and by the nominal

volume ofthe enclosure for the phytoplankton). Algae on the sediment surface were not

sampled and are not included in the periphyton calculation. Phytoplankton chlorophyll

levels were greatest in the early spring in both treatments and controls, while periphyton

chlorophyll levels increased with time to reach a maximum at the end ofthe summer. In

both control and treatment enclosures, the periphyton chlorophyll values were greater

than those ofthe phytoplankton after 4-5 weeks of colonization. The loss ofthe 0.5 m

PVC strips was compensated by averaging total enclosure productivity over the

remaining depths. See Figure 7. Simultaneous productivity measurements are shown in

Table 3, which according to the authors shows that periphyton productivity could equal

or exceed that of phytoplankton after 10 weeks of colonization.

The authors mention that enclosures effects may include excessive periphyton buildup

compared to natural lake conditions, and edge effects creating a nonrandom distribution

of zooplankton.

5
.,..-I....

•

m

a.

LIJ

z

Nct

...

<

200

150

100

50

o ,..,.., , , , , , Fl' , • I , , • [ I , • f •..,.., I • , • , •• ... ·n·' I ' J , , 1 • , , , I'

20

J It40 J 6j :0

TIME (DAYS)

100

5

Figure 1. Atrazine concentration in the water of the three treated enclosures in the first and second

atrazine pulses. Arrows indicate days of atrazine applications (both nominally 100 IJ.glL). (study

figure 1)

6
.'.

30

25

20

20

15

o

0.5 m

....... control

_atraz'ne

2.5 m

1.5 m

3.5 m

:J

J

,

..;..hl'I"'......I"·h'i..t' ..•..i'l·i....Ii'I~

20, 4(l 60;

T J It J i

8(J 1100 120 140 329 0 20 010 (ill

A I S I 0 if A 'J If J I

TIME (DAYS)

130 100 120 140 329

A r s r 0/1 A

Figure 2. Mean ash-free dry weight (AFDW) values for the periphyton in the control and atrazinetreated enclosures at four depths in the first and second atrazine pulses. Error bars represent one

standard error and arrows indicate days of atrazine application. (study figure 2)

7
140 321

Ol/A

8Cl 11I0 Il0

A I s I

.5 m

I

I

I

100 120 140 32t 0 211 40 6D

S I 01/ A t J It J I

TIM£ (DAYS)

60 80

I A

1

J. J/' _~t / /II

/ l

......"i...,."I""........;.,-...~.......,r] ~l...... '44 iiF'i+h "hp " "'hC" ~~

40

It J

20

J

J/

I

I

I

--------~/

/

,¥I

"

"

0.5 m

...-control

-atrazlne

2.5 m

10

40

20

30

110

100

8CI

eo

70

eo

so

30

Ie

c:'20

.!. 10

:::J 0

,.

x

0-

o

II:

o 110 ..J

:J: 100

U 90

III

70

60

&<l

Figure 3. Mean chlorophyll values for the periphyton in the control and atrazine-treated enclosures

at four depths in the first and second atrazine pulses. Error bars represent one standard error and

arrows indicate days of atrazine application. (study figure 3)

8
Atrazine

sp.

sp,

Tetrasporo

Spirogyro

Tefroedron mtl"limum

OedogonLtJm sp. B

Oedogonlum sp.A

Mougeotio sp.

Bufbochaete sp.

Sf ig eoelo nium polymorphum

S. at f en u atum

~:J:-:"'"

»:-::->

••• •••

(/J 40

UJ

<

::E 20 0

-

en

IZ 0

w Control ()

a::

D.

w IOO~

W

> 80 -f60~ <...J

::::;)

:E

40~ ::;)

0

20~I..I

oj

! 34 42 68

1

96

tJ It J I A

TIME (DAYS)

Figure 4. Composition of the Chlorophyta community in the control and atrazine-treated enclosures

in the first and second atrazine pulses. Composition is described using the mean percent

contribution of the common Chlorophyta species (averaged over the four depths) to total

Chlorophyta biomass. Arrows indicate days of atrazine treatment. (study figure 4)

9
A. CHLOROPHYTA

Ualr_zlne

,~ control

J

I !

I:JLil

3.5 m

a. CYANOPHYTA

0.5 m .5 m

4

6

4

2

o

2

e

o JL..JU-J.J:..J.-LL..J..

--------G

4

2

o

c.. BACIU.ARIOPHYC£AE

10

8

6

4

3.5 m

re rv' I v I

l~ v

v

fi

r 4

rI'

9& 329 0 1 34 42 88 06 32.0

SAMPLING DAY

10 -.2.5 m

8

8

4 .~ ~l

2

0 1 34 42 88

Figure 5. Mean biomass values (natural log transformation) for the three periphytic algal groups in

the control and atrazine-treated enclosures at four sampling depths on six sampling days. Error bars

represent one standard error for the mean at each depth (n=3). Atr~zine treatment occurred on Day

oand 35. (study figure 5)

10
,'.

CONTROL

ATRAZINE

30

20

DAY 47 - 49

" 1 -'--1J"'",],\

o+---..,,----~--

0.5 1.5 2.5 3.5

DEPTH (m)

10

20

30

10

...... 0 .+--.,-------r-----+~­

-

I.e

40 ~. 1DAY27-29

Ie>

(,) 30

01

Z

o .a -2

...

4(

...J

! 10 en

<J)

<

0+--..~--_r_--__,.----t IX)

a:

oct 40

(J

Figure 6. Mean carbon assimilation rates for the control and atrazine-treated enclosures for two

measurement periods in the first atrazine pulse and one in the second pulse. Error bars represent

one standard error. The second atrazine treatment was on Day 35. (study figure 6)

11
.-......periphyton

-phytoplankton

t2S

20 aOlATRAZ'NE

1500 \

\

10(;0-1 \ 1 +

5':L~~~ -2& M t J 2S i t ~o I 75A 1

100 S

rlME (days)

CONTROL 1- ~oo I

1500 r

1 /1----1

7"

~,

,j .I / 1 QOlJ:

j

, /+L"

U sao _}Jr

--------.;""·---0 ..---~~ ! "". i'''' . ..J

....

>

:r

l:).

o

a:

o

....

:r

t,)

Figure 7. Mean total chlorophyll values for periphyton and phytoplankton in tbe control and

atrazine-treated enclosures from the day periphyton strips were placed in the enclosures. Error bars

represent one standard error for the mean on each sampling day (n=3). Arrows indicate days of

atrazine treatment. (study figure 7)

12
."

Table 1. Mean water chemical and physical values for the control enclosures (C) and the atrazinetreated enclosures (A) for the first and second atrazine pulse periods in 1983 and for the April 1984

sampling day. * = significant difference between the means (ANOVA) at the 95% confidence level

(p-value < 0.05). (study table 1)

Pulse I (n=18) Pulse 2 (n=36) April 1984 (n=2)

C A C A C A

Oxygen (mgIL, 0.5 m depth) 9.26 9.45 9.90 7.80 * 9.70 10.10

- -- Oxygen (mg/L, 3.5 m depth) 5.67 5.45 6.54 5.20 * 9.70 10.10

Temperature (OC, 0.5 m depth) 18.7 19.1 23.0 23.0 6.0 6.2

Temperature (OC, 3.5 m depth) 10.5 10.0 18.6 18.3 6.0 6.2

Secchi depth (m) 3.2 3.5 3.3 4.4 * 2.4 2.3

DIC (mg/L) 36.08 36.53 23.74 38.54 * 29.9 31.3

N03-NOr N (mgIL) 0.317 0.250 0.235 0.477 * 0.107 0.335

Total nitrogen (mg/L) 0.639 0.667 0.719 0.748 0.846 0.881

Total phosphorus (mgIL) 0.025 0.022 0.021 0.018 0.025 0.025

Table 2. Mean percentage total algal biomass and numbers for the three periphytic algal groups on

six sampling days. Percentages were averaged over the four sampling depths, and standard

deviations (SD) (n=12) are also shown. The second atrazine application occurred on Day 35. (based

on study table 4)

Cyanophyta Chlorophyta Bacillariophyta

Day Controls Atrazine Controls Atrazine Controls Atrazine

Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

% biomass

1 1.3 2.3 2.5 4.5 21.1 20.5 24.8 21.2 77.7 19.3 72.7 19.9

34 1.7 2.6 <0.1 89.6 11.4 88.8 8.2 8.8 11.7 11.2 8.2

42 1.9 3.0 0 90.8 10.9 90.7 5.2 7.3 11.3 9.3 5.2

68 0.9 1.4 0 94.3 6.9 93.2 4.7 4.8 5.9 6.8 4.7

96 4.8 6.3 0 88.8 9.8 96.5 3.0 6.3 7.5 3.5 3.0

329 15.9 22.4 0 26.6 3.8 62.4 18.1 57.0 35.5 37.6 18.1

% numbers

I 30.6 38.7 24.4 22.0 22.1 18.9 17.5 16.3 47.3 25.7 58.1 20.0

34 18.8 19.7 0.8 2.9 62.5 26.2 68.0 16.3 18.7 19.5 31.2 15.5

42 25.1 22.2 0 56.8 23.3 75.1 14.2 18.2 15.9 24.9 14.2

68 14.0 24.8 0 94.3 24.2 60.0 26.0 9.3 6.9 40.0 26.0

96 28.5 28.8 0 55.8 31.2 79.3 18.8 15.7 18.0 20.7 18.8

329 51.4 16.8 0 3.8 4.5 25.7 28.5 44.8 18.2 74.3 28.5

13
Table 3. Total enclosure periphyton and phytoplankton net primary productivity (mg

C/hr/enclosure) for control and atrazine-treated enclosures in July (Days 47-49). Periphyton strips

had colonized for 10 weeks from May 6 until July 18-20. (study table 3)

Controls Atrazine

Periphyton Phytoplankton Periphyton Phytoplankton

1 2812 831 593 1251

:2 ~2~ 4:7.4-.---603 !-OM

3 1017 2104 427 404

Mean 1719 1136 541 899

14
t ·.'.

Data Summary Table:

Effect Magnitude of Nominal Day of Time ])id Comments

Effect Atrazine Study Effect Weighted Recovery

relative to Concentration Occurred Average Occur- if

controls (pg/L) Atrazine so, when

Concentration (see

from Day 0 to comme'!t)?

When Effect

Occurred

Decrease in 10-20% Integrated l'eS='"IJay From dissolved (significant at 100-200/-lglL over Day 107.9/-lg/L 329 (next Table 1.

oxygen p<0.05) 35-137 spring)

Increase in 30% Integrated Yes-Day From

Secchi depth (significant at 100-200 /-lgiL over Day 107.9/-lgiL 329 (next Table I. p<0.05) 35-137 spring)

Increase in 60% Integrated Yes-Day dissolved From

inorganic (significant at 100-200/-lgIL over Day 107.9/-lgiL 329 (next Table I.

carbon p<0.05) 35-137 spring)

Increase in 100% Integrated From nitrate-nitrite (significant at 100-200/-lgiL over Day 107.9/-lgIL No Table I. nitrogen p<0.05) 35-137

Decrease in -50%

periphyton (significant From Fig.2

biomass at p<0.05 at 100-200 /-lgIL Day 36 105.2/-lgIL No and text p.

(ash-free dry most depths 1920.

weight) & days)

Decrease in -50% (not From Fig.3

periphyton significant at 100-200 /-lgIL Day 54 116.6/-lgiL No and text p.

chlorophyll p<0.05) 1920.

Change in

periphyton From Fig. community 100% 100-200 /-lgIL Day 42 110.7/-lglL No 5 & Table. composition 2. _(decrease in

Cyanophyta)

Decrease in

periphyton 70% 100-200 /-lg/L Days 47-49 114.6/-lgIL NR From

productivity Table 3.

(NPP)

Decrease in

phytoplankton 20% 100-200 /-lgiL Days 47-49 114.6/-lgIL NR From

productivity Table 3.

(NPP)

Note: NR=Not Reported

Bolded values are those data points specified in the "Cosm Data Points and Exposure Profiles" spreadsheet.

Time weighted averages are computed from the information in Figure 1. The atrazine

concentrations and sample days were estimated from the graph, then averaged over the

three treatment enclosures. A daily chemograph was constructed assuming linear change

between each sample day. For extrapolation beyond the last atrazine measurement day, a

constant decline at the previous interval's rate was assumed, which resulted in negative

15
concentrations after Day 123; therefore concentrations after Day 123 were forced equal to

zero. Time weighted averages were taken as the cumulative average since Day 0 for each

day. For time-integrated effects, the time weighted averages were themselves averaged

over the days being integrated, i.e. Day 35-137, to construct an average TWA over the

appropriate interval.

See calculations in the linked-Excel spreadsheet, below. In the spreadsheet, treatment-

------a·v~erage-d-eon·een-tra'i-ons-on-s-a-mpl\.1cl-ay,=, 'Vvere-yell-0vv h-i-gh-l-i-ghtecl-te-ea-se--i-n i-flt8F}301at:ieR,.,-.-------

16
.~

Cales:

Day Cone (,.,.) TWA INTEGRATED:

0 100.0 2-78 100 0 Days 3So137 1079

1 1028 2.78 101 Days 47-49 114.6

2 105.6 278 103

3 108.3 278 104

4 1111 278 106

5 113.9 278 107

6 116.7 -1.17 108

7 115.5 -117 109

8 114.3 -117 110

9 113.2 -117 110

10 1120 -117 110

11 110.8 -1_17 110

12 109.7 -117 110

13 108.5 -117 110

i ..-'tu'i~--·u:1·i---I"'iu

15 107.2 -0.11 110

16 107.1 -0.11 110

17 1070 -0.11 110

18 1069 -011 109

19 1068 -011 109

20 1067 -2.42 109

21 104 3 -242 109

22 101.8 -2.42 109

23 99.4 -2.42 108

24 97.0 -2.42 108

25 94.6 -2.42 107

26 922 -242 107

27 89.8 -2.42 106

28 87.3 300 105

29 90.3 3.00 105

30 93.3 3.00 105

31 96.3 3.00 104

32 99.3 3.00 104

33 102.3 3.00 104

34 105.3 17.50 104

35 122.8 17.50 105

36 140.3 1.00 106

37 141.3 1.00 107

38 142.i 1.00 107

39 143.3 1.00 108

40 144.3 1.00 109

41 145.3 1.00 110

42 146.3 -1.47 111

43 144.9 -1.47 112

44 143.4 -1.47 112

45 141.9 ·VH 113

48 140.4 -1.47 114

47 139.0 -1.47 114

48 137.5 -1.47 115

49 136.0 -1.47 115

50 134.6 -1.47 115

51 133.1 -1.47 116

52 131.6 -1.47 116

53 130.1 -1.47 116

54 128.7 -0.85 117

55 127.8 -0.85 117

56 127.0 -0.85 117

57 126.1 -0.85 117

58 125.3 -0.85 117

59 124.4 -0.85 117

60 1236 -0.85 117

61 1227 ·0.85 118

62 1219 -0.85 118

63 121.0 -0.85 118

64 1202 -0.85 118

65 119.3 -0.85 118

66 118.5 -0.85 118

67 117 6 -0.85 118

68 116.8 -0.85 118

69 1159 -0.65 118

70 115.1 -0.65 118

71 114.2 -0.85 118

72 113.4 -0.65 118

73 112.5 -0.85 118

74 111.7 -0.85 117

75 1108 -085 117

78 110.0 ·229 117

77 1077 ·229 117

78 105.4 -229 117

79 103.1 -229 117

80 100.8 ·229 117

81 98.5 -229 116

82 96.2 ·229 116

83 93.9 -2.29 116

84 91.7 ·2.29 116

85 69.4 -2.29 115

86 87.1 -2.29 115

87 84.8 -229 115

88 82.5 -2.29 114

89 80.2 -2.29 114

90 77.9 -2.29 113

91 75.8 -2.29 113

92 73.3 -2.29 113

93 71.0 -2.29 112

94 68.7 ·2.29 1;2

95 66.4 -2.29 111

96 64.1 -2.29 111

97 61.8 -2.29 110

98 59.5 -2.29 110

99 57.3 -2.29 109

100 55.0 -2.29 109

101 52.7 ·2.29 108

102 50.4 ·2.29 108

103 48.1 -2.29 107

104 45.8 -2.29 106

105 43.5 -2.29 106

106 41.2 -2.29 105 17 107 38.9 -2.29 105

108 36.6 -2.29 104

109 34.3 -229 103

110 32.0 -229 103
~. ..

Reviewer Comments:

Compared to the other periphyton study from this experiment (Hamilton, et al., 1989),

this study was straightforward in it presentation of methods and results, and no severe

methodological shortcomings were evident The descriptions ofthe methods used were

terse, often relying on references for further description, but gave basic summaries of all

techniques. Like most ofthe various Hamilton, et al., papers, Lake St. George is not

----~des_cr-i·becl-wel1~;_backgr6l:incl-lev·e-Js-q·f-atrazin'Vin-t-he-Iake-are-fi0t-m.·eas·a:r:eg,a:r-1-a-t:h'e~-------­

surrounding land use and atrazine runoff potential is also not explained. -The statistics

used in the paper were insufficient in that tests for homogeneity of variance and specific

ANOVA tests are not described, and "significant" results throughout the paper are not

assigned p-values. One exception is Table 1, which apparently uses a p-value of 0.05,

which can perhaps be assumed for the other "significance" statements as well. The

authors attempt to compare periphyton and phytoplankton productivity on an enclosure

scale; however, this analysis is not useful because the enclosures are artificial substrates

that would not be available in a natural lake setting.

The most fundamental problem with the Lake St. George enclosure experiment is the

enclosures themselves. In this study, the PVC is described as "yellow", which implies

that it may be opaque. It is expected that periphyton colonization would result in opaque

walls after colonization occurs. As the authors themselves mention, the periphyton

buildup on the enclosure walls can lead to spatial variability in certain parameters (they

mention zooplankton density). It is quite possible that the spatial patterns created by the

wall effects make the periphyton colonization success in the sampling unit substrates

dependent on the sampling location. Sampling location may therefore be a confounding

variable in the periphyton analyses, due to the nonrandom spatial patterns created by

opaque, periphyton-covered enclosure walls.

Description of Use in Document (QUAL, QUAN, INV): Qualitative

Rationale for Use: : Results confirm that atrazine concentrations of 100 Jlg/L

inhibited production ofperiphyton within limnocorrals and altered the compostion ofthe

periphyton community.

Limitations of Study: No p-values provided for "significant" results. Enclosure wall

effects could confound periphyton analyses due to random locations ofthe sampling units

within a spatially patterned environment.

Primary Reviewer: Sara Hendrix, M.S., Staff Scientist, Cambridge Environmental Inc

18
Secondary Reviewer: Anita Pease, M.S., Senior Biologist, Environmental Fate and

Effects Division, U.S. Environmental Protection Agency.

/f1-&jL (,( 'J II(

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