THE EFFECT OF THE INTERNAL SEICHE ON ZOOPLANKTON DISTRIBUTION IN LAKE OTSEGO

James Kevin Hill

Biological Field Station Cooperstown, New York

Occasional Paper No. 16

Biology Department State University College Oneonta Abstract

The causes for the i~itiation anrl perpetuation of the internal seiche in Lake Otsego an~ the possible consenuences of this water

(,over. ent on zooplankton dis triuut iOel '-'ere e::ar,inc,]. Deterninat ion of

\ the internal seiche was acco~plisherl by recorJin3 the position of various isothenls at a specifierl point on the lake over a period of trw \"onths.

Recor~in\!s were usua 11y taken three t hies a riay.

It becate readily obvious that the i'lterlal seiche vas ~lOt a sirip1.e oscil.latio:l. of the \o:atcr rass out rather a constantly ;olifie 1 liOVClent which n'flectei the actio'l.s ()f the surface vi'l,Js an--l tn a lesser e);tent the t, orpholo\iY of the lake basin.

The a: ount of I ovel,e:ct 0estr:n,7e: on the water mass by t;1e intf'rnal seiche is cons irierab 1e, yet 1.Jecause this pheno\,'enon does not typica 1.1y

[anifest itself in obvious surface rlisturbances it is often unappreciated.

Plankton populations are greatly influenced by the internal seiche. A corr-puter I,odel developed usin~ the characteristics of Lake Otsego was constructe3 which de~ionstrates the e~pected redistribution of various zooplankton.

A lir.iterl field investigation was perfon.ed in an attevpt to correlate the r.:odeled distribution of zooplankton with eL.pirical evidence of seiche inducerJ zooplankton redistribution. Initial finrlings support the ti,odeled 'It effect. Waters enriched or deprived of zooplankton were found which corresponded to the situation predicted by the rtlo.lel. Such variation in zooplankton densities ti~y affect the distribution of the planktivorous ciscoe (Coregonus artedii), a favorite sport fish of the area. TABLE OF COKTE:t~TS

IntroJ\.lction 1 hetho..ls and l';aterials 9

IdentifyinJ the seiche 9

Con,puter n,odel 11

Correlation study; COI:iputer Liodel and ecpirical evidence of seiche induced zooplankton redistribution 12

Discussion of Results 15

Description of t!le internal seiche; initiation and perpetuation 15

Meteorological effects 21

Morphological and physical effects 31

Flow in a two layered ~asin 32

The '"odele'] re'listrie:,ution of the zooplankton resultin0 rrOL, inter­ action with the internal seiche 35

Field studies S2

SC

I. Tel"pera ture ;Jrofi le Lla ta of Lake Otseci0 fronl June23-July24, D8') 56

II. COL:puter pro~ram use,j to sir"ulate zO-:>:J lan:(t.'J:l ill~2rac tion 1;,\:i t~; tlll~ intc:-:1al s'2iche ':0

~iteratur2 cit2~ 01 1.

Introduction

Lake Otsego is a dimictic lake. During the summer season warmer

less dense water (the epilimnion) will be present in the upper portion of the water column. Colder denser water (the hypolimnion) constitutes

the lower depths (Fig.la). As the season progresses the epilimnion will increase in temperature and decrease in density, while at the same

time the deeper hypolimnion waters will remain comparatively cold and dense. A boundary layer (the thermocline) formed between these regions of changing densities becomes established and effectively hinders the mixing of waters between these two strata.

Once the thermocline is established any subsequent movement of the water, usually as a result of ,,,ind action, will result in the formation of a long standing wave or seiche. A standing wave is a wave which oscillates about a point or node which is in a fixed or standing position.

The term "seiche" was originally used to refer to the periodic drying of shallow littoral zones.

The seiche may be in the form of a standing surface wave, which is a wave of small amplitude and results in far less movement of water on a volume basis than its counterpart, the internal seiche (Wetzel,

1975). The internal seiche is a standing wave perpetuated along the thermocline and as such causes movement of the entire water mass as the epilimnion and hypolimnion oscillate relative to one another. In this work the term "seiche" is used synonymously ,"ith "internal seiche" and will refer only to this phenomenon unless so stated.

My study involves the theoretical effects of an internal seiche on plankton distribution in Lake Otsego. First, I determined empirically the factors which influence the initiation, perpetuation and dampening thermoeline~r-----+- -J wind begins (al

Ie)

!~ \ \~ maximum flow maximum flow -----~ ~r ------3. of the seiche in Lake Otsego. Secondly, I used a computer to model zooplankton movements in Lake Otsego reflecting seiche activity. That part of the study \vas followed by a field check to Je termine empirica t agreement with the predicted results.

Rhythmic oscillations in the level of various isotherms in Loch

Ness were recorded in 1904 by Watson during his intensive study of that lake. Although Forel (1895) is credited with introducing the term

"seiche" it was Watson who first correctly interpreted the oscillation.

Watson's claim that the oscillations were standing waves established on the interface between two bodies of fluid differing in density was confirmed by Wedderburn (1912) and Wedderburn and Young (1915).

The internal seiche is a well established phenomenon occurring universally in all enclosed bodies of water exhibiting stratification

(Mortimer,1952). The phrase temperature seiche is often used interchange­ ably, however internal seiche is preferred as this includes stratification due to solutes (salts) as well as temperature (Mortimer,1952).

An internal seiche is commonly established by wind drag on the water surface. A seiche may ~e developed when, in response to the wind, epilimnion waters are piled at the leeward end of the lake while hypo­ limnion waters are concentrated at the windward end (Fig.l) producing a tilt of the thermocline. The cessation of wind activity allows the lake to eouilibriate. This equilibriation manifests itself as the internal seiche (as well as the aforementioned surface seiche), a phenomenon in which the entire water mass of the lake is involved in the dissipation of previously stored up wind energy. Such a response should produce a fundamental wave (the wave with the lowest frequency) and subsenuent harmonics (integral parts of the fundamental which exhibit greater or 4, higher frequencies). Usually, in a basin of regular shape, these harmonics are resolved to producing a uninodal resonance (Wetzel,1975).

Higher harmonics tend to dampen out rapidly thus the most common sustained motion produced by the internal seiche is a uninodal rocking motion with the node usually near lake center (Mortimer,1952). Multi- nodal seiches may be quite common in very large lakes where localized wind of short duration may produce responses in limited areas of the lake. Lake Otsego has been found to exhibit a uninodal internal seiche, with the nodal point situated near lake center (Harman et !l ' 1980).

Lake Otsego, formed during the last glacial advance, has the morphology typical of a finger lake. The lake axis lies in a northeast- southwest direction. Although this position does not coincide with prevailing winds it does allow for considerable fetch for north and south winds. This fact, in combination with the near rectangular basin morphology (11.1 km effective length, maximum width 2.5 km, and maximum depth 50.6 m (Harman ~ !l,1980) and the many theoretical and modeled works on basins of this design (Watson,1904 and Mortimer,1952) makes

Lake Otsego an ideal lake for the study of the internal seiche and the conse1uences of such a phenomenon.

\o/atson (1904) derived a formula for determining the theoretical period of an internal seiche (T) in a rectangular basin of uniform depth. Hhile a natural basin of this design does not exist, the ob­ served period in Lake Otsego, or any other lake of similar basin morph­ ology, can be closely approximated by this formula. Watson's formula is given by:

T 2 (1) R~h*,>i:) (1) i#+j2!:. t1 e 5.

where 1 the length of the basin g = acceleration due to gravity e thickness of the epilimnion h = thickness of the hypolimnion ye density of the epilimnion ~h density of the hypolimnion A= the wavelength (2*1) C = the phase speed

Such an approximation alone can be misleading if one attempts to predict the future positions of a given water mass or isotherm on the period determined from data collected at an earlier date ..This is because of the dampening or reinforcing effect of variable winds on the seiche and the effects caused by the morphology of the lake basin. The latter reason is an often overlooked factor which can greatly effect seiche activity. Basins with topographic features that restrict water movements will possess an observed period longer than that calculated by eq.l (Wetzel,1975). Such conditions exist in Lake Otsego (Fig.2).

The presence of Sunken Island at the lake's north end forces a diversion of the waters moving in response to the seiche. An extreme example of a topographically enhanced internal seiche period was reported by

Beauchamp (1954) when he observed a seiche in Lake Victoria with a period of thirty days. The predicted value by e~.l would have been on the order of five to seven days. Such an exaggerated period resulted from the presence of numerous channels leading to isolated peripheral pools.

A third factor which causes deviation from the predicted periodicity is the inherent friction created at the thermocline as the epilimnion and hypolimnion stream past each other during normal seiche activity

(Hutchinson,1957).

Hutchinson (1957) suggests that these dampening factors decrease the overall energy of the seiche by 25% per period. Heaps and Ramsbottom 6.

OTSEGO LAKE IGlIMMERGLASS) onlOO cou-n. 11M vQflIIt

nAn UNfVlQITV 0' 11M 't'OttK COLLJOI AT OflfIONTA ICLOQlC.U "llD .TATlOfll cOOPt••~.,.,'t'

SO am a 1000 m ! ! ecale in meters

~~'" '-:'[;:;(';<1 L,';',/' '~h' :':Jd,· i:~ ~.:dic"t~ed '1::w3l'\d t.he '~:lree ~ile P'lint :c,'c'lrding ~ t -.:,: i:) 'c" ® .

SUSQUEHANNA RIVER 7 •

(1966) reported approximately a 35% damp per period in Lake Windermere.

A dampening function as determined by Kamykowski (1973) was used where indicated in my work. The eluation

a = a-Da ( 2) lOT relates amplitude (a) directly to the dampening factor (D) and indirectly to the period (T). It is important to note that the term dampening refers to a decrease in amplitude, consequently reinforcement refers to an increase in amplitude.

The time of the year and the motion of the rocking seiche reluires that the location assigned for seiche monitoring be given due consider­ ation so that erroneous assumptions are not made based on transient water conditions. Wedderburn (1911) stressed this point when he declared that "Observations should demonstrate to other observers the necessity for more careful investigation of lake temperatures and the futility of basing comparisons between lakes on observations made at one point and at considerable intervals of time."

If one assumes the lake to be a two layered system, based on thermal differences, it becomes possible to measure the volume and velocity of water flow due to the seiche. Such an assumption is accurate in describing many aspects of seiche movement as Mortimer (1952) has shown in his use of two layered models of lakes.

Figure 1 shows a longitudinal section of a two layered basin subjected to a uninodal internal seiche. The period can be calculated bye,!.l. The volume of water transferred during each half cycle (Fig.ld­ lh) is e:lual in each layer (ie. epilimnion and hypolimnion) and consti­ tutes a major portion of the water mass of the lake. The mean nodal velocities in the epilimnion and hypolimnion during the half cycle are 8 .

given by 2 sl 12Te (3) and 2 -sl 12Th (4) respectfully, where s represents the maximum slope along the thermocline and 1 is the basin length. The flow is opposite in each layer as indi­ cated by the difference in sign. During the following half cycle (Fig.lh­

ld) an e-;ual but reversed displacement from the first half cycle would

theoretically occur. However, owing to surface disturbances, a particle is unlikely to return to its original point.

The volume of water and velocities of these movements can often be substantial. Mortimer (1952) found a maximum net velocity along the thermocline of Lake Windermere of about 3cm/sec. Water movements of such magnitude may have a profound influence on plankton distribution within the lake. Indeed, others have sug~ested such a conse~uence of the seiche (Thomas,1951 and Mortimer,1952). 9.

Methods and Materials

Identifying the Seiche

The presence of seiche activity can be most easily ascertained by noting changes in the relative position of the epilimnion and hypo­

limnion. Heasurements of this type are determined by monitoring a given isotherm and plotting its position in the water column with respect to time. The result is a perceivable rising and falling.. of the isotherm which is synchronous with the rocking seiche.

Preliminary monitoring of the seiche began at points approximately

2 km north and south of the nodal center. (The node was determined by

Harman et al (1980) to be. midway across the lake from Bissell's Point, as shown in Fig. 2). A third monitoring site was established off Rat

Cove at a depth of approximately-20 meters. It became readily apparent that much of the information gained was redundant, as the positions of the isotherms in the northern quadrant of the lake could be deduced by readings gained in the southern quadrant. For this reason the northern monitoring point was abandoned. Similarly the Rat Cove monitoring site was dispensed with as it proved less than satisfactory since deep hypo­ limnion waters could not be monitored.

All subsequent data collections (with the exception of an intensive lake wide search for hypolimnion waters in contact with the surface, to be discussed later) were performed at one point, approximately 2 km south of the node off 3 Mile Point, in 35 meters of water. This is station 3HP (Fi'g.2). The use of only one station to determine seiche activity has been shown to be an effective method (Mortimer,1952 and

Henson,1959) when fre~uent recordings are performed.­

Sixty-three temperature profiles of the water column at 3MP were 10. recorded from June 23 through July 24, 1930 (see appendix 1). Initially the water temperature was recorded only at the surface and at depths of

5-2Om, 25m, 30m, and 35m. Intermediate depths were not recorded. I unfortunately assumed that I could accurately extrapolate missing depth temperature values from the values I had recorded. Beginning on July

9, 1980 complete temperature profiles were attained from the surface through 35 meters at one meter increments.

Temperature profiles were obtained using a Montedoro-Whitney

. 0 thermistor w~th accuracy of 0.5 C. (A note should be made here regarding the use of the thermistor on exceptionally hot days. If left on board or placed in direct sunlight the thermistor probe and wire absorb consider­ able heat, causing the subse~uent reading to be inaccurate by as much as

0 1 or 20 C. Though I recognized these anomolies, much time was wasted in taking the inaccurate profile, realizing the problem and returning the thermistor to the ambient water temperature, then retaking the profile).

In order to determine the observed periodicity of the internal seiche it became necessary to record two or three profiles each day, normally scheduled for 0900, 1300, and 1600 hours. On extraordinary days, days in which a major wind change had occurred or a weather front passed over, as many as five recordings were made to insure the accurate portrayal of the seiche.

Temperature profiles were taken from on board a 14 foot aluminum john boat. All profiles were recorded while the boat was anchored at the 3~~ station. The thermistor probe was attached to a weighted line to assure a vertical decent. The recording of a temperature profile was usually accomplished by two people, a reader and a recorder. Along with the temperature profile, the air temperature, wind direction and wind 11.

force were determined. Copious field notes were also taken on the condi­ tion of the lake surface (ie. presence of Langmuir helices and distance between such, breaking of surface waves, etc.). Wind direction and force were determined on board with a hand held anemometer (accuracy less than 3.3 km/hr. (2ulph)) and a compass. The accuracy of the anemo­ meter was limited and would not be suitable for exacting meteorological standards, it nonetheless provided me with good general information on daily wind conditions. Its accuracy was well within my needs.

After each temperature profile was recorded the data were examined at the field station and subjected to Watson's formula (eq.l) to determine the theoretical seiche period. By analyzing the data at this time I was able to determine any incongruities between the observed, theoretical and my own predicted values and decide whether additional readings were required which were not previously scheduled.

Throughout the summer of 1980 a stationary weather station was maintained near the Biology Field Station docks. Its purpose was to insure the recording of any frontal passage and subsequent change in wind direction which may have occurred during the night hours. It was equipped with a recording thermometer and an aneroid barometer capable of recording the maximum high pressure and the minimum low pressure during a given period. This station was checked twice daily, in the morning and evening. Data were recorded and the in6ttuments reset.

Computer Model

The computer generated model was used to predict the effect of the internal seiche on the redistribution of various zooplankton. The modeling techniques follow those of Kamykowski (1978). The program

(FORTRAN IV on Burroughs 86810 Large System) was designed by James 12.

Greenberg (S.U.N.Y. Oneonta Computer Services Center) and myself.

The basis for the program was a series of e~uations derived from the

uninodal standing wave equation (Resnick and Halliday,1968). The model

simulates the redistribution effect in Lake Otsego by computing the

position of the diurnally migrating zooplankton in regards to the motion

of the internal seiche.

Correlation Study; Computer Model and Empirical Evidence of Seiche

Induced Zooplankton Redistribution

In an attempt to show actual seiche induced redistribution of

zooplankton I first monitored the seiche by the temperature profile method described earlier. Readings were taken at 3MP from August 15

through August 22, 1981 so that a description of the seiche at that time

could be made. When the characteristics of the seiche had been ade­ quately described I began my collection of zooplankters.

Surface collections were made at 1900 hrs. on August 22 and

August 25. at both the north and the south ends of the lake. For reasons discussed later this was probably not the best time to attempt

to collect representative zooplankters. Under these conditions the model would predict that only the fastest migrating zooplankton were at

the surface at that time. However, my correlations re~uired only a

1uantitative description and not a ~ualitative one. I was looking for

trends in the redistribution of numbers of zooplankton, not a description

of the taxa.

Prior to the collection of zooplankton a temperature profile was

taken to assure the predicted position of the seiche was accurate.

Surface collections were made with a Clarke-Bumpus plankton tow suspended

from the "A" frame of the research vessel Anodontoides. The depth of 13 •

the tow was less than 0.5 meters and the collection time was 60 seconds.

All collections were made from the vessel Anodontoides, which moved at a constant velocity into the surface current. Upon completion of each

tow the Clarke-Bumpus was closed and brought to the surface. The col­

lection cup was disassembled and the organisms ,.,ere washed with 1070

formalin solution into a one gallon jar. The meter reading was recorded and the net washed to prepare for the next tow.

In the laboratory each of the preserved plankton samples was well mixed prior to the removal of a 1 ml aliquot. This 1 ml sample was obtained using a Henson-Stempel pipette. The sample was placed in a

Sedgwick-Rafter cell and the total field (copepods and cladocerans) were counted. From this 1 ml plankton concentrate the density of organisms in the lake water sampled was found by the following formula

(Lind,1974)

organisms per (organisms per ml of concentrate) * liter of lake (volume of concentrate) * 1000 (5) water volume of lake water filtered (ml)

Cladocerans were included in the sample despite the fact that earlier reports concerning the organisms in Lake Otsego seem to indicate that they may not follow the classical migration pattern as stated in

Hutchinson (1967) (Harman,1973). Cladocerans were included in my study for two reasons. First, observers on other lakes describe the movement of the cladoceran Daphnia pulex as typical of diurnally migrating zooplankton, and these same observers furthermore implicate water movements in aiding the redistribution of the zooplankter (Ragotzkie and

Bryson,1953). Secondly the possibility of certain ambiguities exist in the earlier Lake Otsego data in regards to sampling procedure

(Harman, 1982) . 14.

The collections from the north and south ends of the lake taken on August 22 were compared statistically by a chi s1uare evaluation.

A similar evaluation was performed on the data collected on August 25,

1931. 15.

Discussion

Description of the Internal Seiche: Initiation and Perpetuation

Surface winds are the foremost builders, perpetuators and modifiers

of the internal seiche (~10rtimer,1952). The effects of wind on the seiche

may either be reinforcing such as those recorded on July 15, and July 2~,

1980 or dampeninG as witnessed on July 22,1980.

Reinforcing winds serve to:

1. remove epilimnion waters from the windward end of the lake

resulting in a drop of the mean epilimnion temperature at that

position. Likewise an opposite effect would occur at the lee­

ward end, where epilimnion waters pile up and the mean epi­

limnion temperature at that point would increase

2. increase markedly the amplitude of the isotherms surrounding

the thermocline

3. in certain cases cause an increase in epilimnion depth(e). An

increase in (e) in e(luation 1 results in shortened periodicity.

While dampening winds produce:

1. decreases in amplitude of isotherms near the thermocline

2. surface turbulances

3. effective mixing of surface waters, forcing isothermal

conditions to depths of four meters.

Isotherm recordings for near midday temperatures on L. Otsego at

3MP are presented in Fig.3 for the period of June 9 through July 24, o 1980. The 21 C isotherm is representative of the epilimnion waters, o whereas the 13 C and 13 0C isotherms are boundaries of the metalimnion.

0 00 The 10 C, 8 C and 6 C isotherms are all indicative of hypolimnion temperature flucuation. The water mass with the nearly isothermal ~

June July 1 2 10 11 ;12 13 ,14 15 16 17 18 !20 :21 22 23 24 o I 23 I 24, 25 11 26 I 27 30 6 7 8 9 19 28,29 i 1 1 I b- 4 '_ 5 21.0°

5

10· ... (lI'" ~ 15 :2: c: ..c:

0 20 - 0.Q) 0

25 (:_0 0

30

35

I I I I Fig.3. Flucuations of the (joe, (l°C, 11)oC, 13°C, lSoe and 21°c isothcrn;s observed at the 3tl1' recording station on Lake OtSt'go [rl"'l .July 9-Ju1y 20, l'Jt)J.

t-' .0\ 17. temperatures, hence less density difference (ie. waters surrounding the

o 0 0 6 C, 8 C and 21 C isotherms) exhibit the most pronounced amplitude, while those waters which are near large thermal gradients (waters of o o. the 18 C and 13 C ~sotherm) show a much dampened vertical movement.

The dampening of the amplitude at the thermocline attests to the difficulty in mixing the epilimnion and the hypolimnion waters. As stratification intensifies the thermocline acts as a slip plane upon which the epilimnion glides over the hypolimnion.

Two temperature profiles taken on June 24 at 3MP indicate a movement of the epilimnion waters and a shift in the thermocline (Fig.4).

During the time of the first recording (1230 hrs.) the wind was calm, however by 1500 hrs. a south wind of 10 mph (16 km/hr.) had developed.

The drop in the surface water temperature at this time may be indicative of the type of hydrostatic disruption caused by the wind stress on the lake as warm epilimnion waters are transported to the leeward end of the lake (in this instance the north end) while cooler waters of the hypo­ limnion are upwelled at the windward end of the lake resulting in a rise of the thermocline. Such a condition would be preparatory of the initiation of the seiche (Mortimer,1952).

The rhythmic motion characteristic-of the seiche is by no means a simple oscillation. Aside from the fundamental wave, harmonics are produced which for a short time will have an influence on water movements.

A second complicating factor in the seiche oscillation is the fact that the periodicity of the seiche is related to the density of the waters moved. It is expected that each isotherm will behave slightly different than all the others, producing a very complex movement of waters (Bryson and Ragotzkie,1960). Temperature in °c 15 16 17 18 19 20 0/ I I I I I I I

2

Ol ~ 3 <: ..c: D- Ol 0

4

6

Fig.il. Two tel"perature profilcs taLcll un Junc 2/1, 198,) inJicate a \lIOVel"cllt lJr l'pi­ 6 .. lin,l1ion waters associated with chal16in~ ..... in<..l conditions. Winds at 1230 hrs. were calm while those at 1500 hrs were frOl" the south at lOlllph. 71 ", I I I I I I -03 19.

Once established, the overriding modifier of the seiche is the energy derived from surface winds. Although basin morphology creates definite frictional interferences, it is highly unusual for basin influences to dampen a ~eiche to unrecordable extremes prior to the action of reoccurring surface winds, which may be of the reinforcing or dampening type. At no time during my study was the internal seiche imperceivable. though it did exhibit variations in periodicity.

Temperature changes at a constant depth (7.0 meters) were monitored extensively at 3MP from July 7 through July 11. 1980. A graph of the seiche was plotted from these data (Fig.5). Point K represents the o maximum temperature recorded (19.8 C) at the 7.0 meter mark during this period. I have made the assumption that this temperature is also the maximum temperature attained at the 7.0 meter mark during this period.

This assumption is based on the fact that two recordings, points J and

L taken shortly before and after point K show the slope of the 7.0 meter isopleth, representative of the thermocline depth, to have changed from

(+) to (-). This indicates a temperature maximum was reached in the time interval between points J and L. Thus the maximum must be near point K. (Similar assumptions are used in further graphs of theoretical plots and empirical data). Temperature data obtained for point K was used in eq.l to calculate a theoretical period of approximately 20 hours.

Point H was chosen to represent the lowest minimum extreme or temperature at the 7.0 meter isopleth (points E and B are lower but the time interval between these points and K is large and greater than one period, therefore it is possible other factors may have been responsible for this positioning, ie. prior winds). A theoretical curve was constructed based on the calculated 20 hour period and on the temperature extremes 7/8 II m 1200 hrs 2400 hrs 1200 hrs 2400 hrs 1200 hrs 2400 hrs 1200 hrs 2400 hrs 1200 hrs 2400 hrs

21°

Temp in CO

20°, a

H Be Ee N

Wind 100 Velocity in mpH squared 0 I • • • • • •• • • • iii. • I

100 s

~I • Fig.5. Observed temperature changes of the 7.0 meter isopleth at 3HP frolll July7-Julyll are represellted by points A-R. The curve represents the theoretical variation in teltlperature at 7 lJlctC'rs. The bar ijraph inrii­ cates the ~7intl velocity in lJlph squared and wind direction either frolll northern quadrants or southern qua(lrants. .~ at points K and H.

Wind conditions recorded at 3MP at the time temperature readings

were taken are also depicted in Fig. 5 as the velocity observed in mph

squared. The stress due to wind on the water surface is proportional

to the square of the velocity (Sverdrup, ~ al,1942). Winds from the

north are shown as bars drawn above the line, winds from the south as

bars below the line. The length of the bar is proportional to the velocity

squared.

Henson (1959) performed a similar test to show the presence of

internal seiches in Cayuga Lake, New York. He concluded that if the

observed points coincide with the constructed curve then the fluctuations

were indeed caused by an internal seiche. The plotted points A-R

obtained from observation do fit the theoretical curve and clearly show

the presence of the internal seiche in Lake Otsego.

Meteorological Effects

Strong winds may produce surface waves, convection cells (Langmuir

currents) and other visually obvious surface phenomena. However the

effect of such winds on the internal seiche are far more subtle and

less obvious.

On July 15, 1980 a moderately stiff southerly wind of approximately

15 mph (24 km/hr.) associated with a frontal passage began blowing on the

lake. Figure 6 portrays the expected removal of warm epilimnion waters

from 3MP on that date. However further examination shows that the winds

of the fifteenth were reinforcing the seiche, that is they were blowing

in the same direction that the epilimnion waters were flowing. Plotted

in Fig.7 are the observed temperatures at a constant depth of 7.0 meters

for July 14 to July 17, 1980. The curve is constructed, as shown before, 11 '.. 7/15 7/16 7/17 O. • i I I I I" I I I I I 2400 hrs 2400 hrs

2

3

~ !.. 4 ~ .= t.. 5 Q

6

7

8

9

Fitj.(l. ObservEcd tClllpcrature variations in the 21°C and the YJ.6°C isotherms between July III

,N '..J ..

7/14 I' I I 1~00 2400 1200 2400 1200 2400 1200 I Temp in 0C 2-tL 0'

T

z •

A'

N

100 Wind Veloci ty 0 in mph ---..··-T-·~ -1iil!--.-.rT·--~-'-----_· squared 100

200

~-~~, .--_.~--_._,---,--,-_.~~~~~-~=~--~-= --~------_. -"­ Fig.7. The observed tenperature at a constant depth (7n,) at 3111' bet\I!een July ILl and July 17, replescnted here by points S-F'. The curve represents ttle theoretl.cal' change in temperature at 7 \1,ctprs. The stl'ong reinforcing effect of the southerly winds late on July 14 have altered the curve position on July'S.

·N lAB ~ based on points T and V to produce a seiche with a 20 hour period.

Points S-Y appear to fit nicely on the projected curve of the 7.0 meter isopleth. Figure 6 is indicative of the change in position o (ie. amplitude) of the _19.6 C isotherm at 3MP for the same period, the o mean amplitude of the isotherm on July 14 is 1.15 meters (the 19 •. 6 C isotherm is representative of the lower boundary of the epilimnion on this date).

However, points A' through F ' in Fig.7 do not fit the constructed

20 hour curve as would be predicted. A curve based upon points D' and

A' and a calculation of the periodicity using these points indicates the existance of a seiche with an 18 hour period.

Keeping in mind that the curve in Fig.7 is of the temperature at a constant depth of 7.0 meters, an ascending portion of the graph represents increasing temperature. at that depth, as would be expected when the seiche is between position (d) and (h) in Fig.l. Exactly the reverse is true of a descending curve, it represents a decrease in temperature, as when the seiche motion is similar to that illustrated between position (h) and (d) in Fig. 1. South winds which occur when the curve is descending tend to be reinforcing. North winds however would accumulate warm surface waters at the south end and would have a dampening effect if they occurred while the curve was descending.

Figure 7 illustrates the reinforcement quality of the winds of

July 15 and the changelnperiod and position of the 7.0 meter isopleth between Y, Z, and AI.

During this time of wind stress the windward end of the lake

(in this case the southern end) witnessed a drop in mean epilimnion

o 0 temperature from 20.6 C to 20.2 C, and the thermal gradient in the 25 .. metalimnion (8-14 meters) remained nearly constant (1.46-l.430 /meter).

It is assumed that the opposite would be true at the leeward end where piling up of epilimnion waters would produce a dramatic thermal gradient at the thermocline and hence accentuate the density barrier. Mortimer

(1952) reported just such an occurrence in Lake Windermere's south basin following strong north winds. I have no data to support this proposal for this given time period though later studies (see discussion of July

24, 1980 data) do substantiate this assumption.

It is entirely possible that under certain conditions (ie. moderate winds of long duration) hypolimnion waters may upwell at the windward end to such an extent that they contact the surface or come close enough to be effected directly by the surface winds. Upon approaching the surface the upwelling waters are incorporated into the same surface drift which removed the epilimnion. This would result in an epilimnion of lower mean temperature and of increased depth, and in fact may consti­ tute a major means of mixing hypolimnion and epilimnion waters during stratification (Mortimer,1952).

If 7.0 meters is the mean thermocline depth at 1MP on July 15, and we assume an amplitude variation of 2.0 meters for an isotherm indicative of the lower boundary of the epilimnion (eg. 19.60 C) then we can predict the magnitude of the amplitude at the south end of the lake as follows

a ::0 ....:.L a ::0 amplitude at x x xl x ::0 distance from node ( 6) al ::it amplitude at xl

xl ::0 distance from node

Substituting values for the distance to the node from 3MP (x) and the southern end of the lake (xl) along with the observed amplitude of the 26.

o 19.6 C isotherm at 3MP (a)(1.25km, 5.25km, and 2.Om respectfully) we

obta.in a maximum amplitude at the southern end of the lake on July 15,

1980 of about 8.4 meters. This would be enough to cause the hypolimnion

to contact the surface~~nd be incorporated in the surface water drift.

Such conditions are probably the major influence in causing changes in

observed seiche periodicity as redistribution of water density is achieved

by the mixing. Although I was never able to detect hypolimnion or meta­

limnion contact with the surface, I concur with Mortimer that such an occurrence would not be unlikely and indeed may be common place when wind conditions are proper. Harman (1982) has observed this phenomenon

in Lake Otsego. I believe my inability to detect deep water upwelling

to the surface under the aforementioned conditions is due in part to the shallowness of the lake at the north and south ends. Such a morph­ ology would tend to dampen the seiche and may act to pool epilimnion waters.

On July 22, 1980 a very different effect was produced. South winds of up to 20mph (32km/hr.) were recorded at 1000, 1230, and 1600 hrs. with a 25mph (40km/hr.) wind recorded at 2000 hrs, indicating a steadily blowing wind. The day prior to this, July 21, the theoretical seiche period was approximately 17.6 hrs. (based on the temperature profile of July 21 at 0930 hrs.) and the mean change in the amplitude of the 20.60 C isotherm, which at this date represented the upper limit of the thermocline, was 1.41 meters (Fig.8). July 21 had been a relatively calm day. Initially the winds of July 22 served to reinforce the seiche as shown in Fig.9. By 1400 hrs. on July 22 the seiche had reversed itself and the strong south wind became a dampening influence on the now

~uthward flowing epilimnion. As might be expected considerable turbu­ 7/21 7/22 7/23 7/24 oI I I I I I I i I I 1200 2400 1200 2400 1200 2400 1200 2400

2

3

::: 4 ...Ql Ql :!: .: 5 ..c: ...C. ~ 6

7 - ~ ~ ~ aL / " 20.6°

9

, I I I I I I I I _ J Fig.8. The 20.6°C isotherlll at 3HP frOnt July21-July24. The isotherDl is indicative of the lower boundary of the epilin,nion on this date. The amplitude is greatly decreased due to the Jawpening effect of the wind.

N "

~~ ·"t, "':~1"~~~_""''''''''~_''''' ,...... e .,.,.". ...."'~,·.;-·...'~,~ ....~r. "~,,,.' 1200 2400 1200 2400 1200 2400 1200 2400

Tempi 'in °C' 23

R'

22°

21° N [40Q]

300

20' ~- [200] ,Windl ~~- 100 IV~locityi ',In~-~ mph _ _ F. I ,L .---- I 01 •• • :Squared!

100

200

300

S 400l , I ,. • • I I I I I , . Fig.9.'Points C'-R' are the observeJ teniperatures of the ]n,eter isopleth frolll July21-July2LI at JtIP. The curve is the theore t ica1 tewpera ture change caused by the intern~1 seiche. North \.;io<15 of the 24th are reinforcing while \.;inds of the 22ncl are strongly dampening. ' N 00•

,~ 29.

lence resulted at the surface as southerly moving epilimnion waters were buffetted by the south winds.

The turbulence acted as an effective means of mixing the epilimnion.

A temperature profile taken at ZOOO hrs. (Fig.lO) exhibits isothermal conditions to 4.0 meters. Well defined Langmuir helices were also ob­ served- at this time. The dampening action of the winds produced a theoretical period of l8.Z hrs. based on data of July 22 at 1600 hrs, o and caused a dramatic drop in the amplitude of the ZO.6 e isotherm

(Fig.8).

July 23 was a calm day.

North winds on July 24 afforded an excellent opportunity to study the isotherm build up at the south end of the lake. Figure 10 shows the increase in water temperature at the south end of the lake in response to the north wind. By projecting the July 22 calculated period of 18.2 hrs. it is possible to demonstrate that these north winds of the twenty-fourth were of the reinforcing type, as the temperature of the

7.0 meter isopleth curve is rising. The consequences of the event are: o 1) a rising of the mean epilimnion temperature from 23.0 e to 23.60 e at

3MP during the time of the north wind, Z) a sharp rise in thermal grad­ ient in the metalimnion to nearly ZOe/meter, and 3) a quickening of the period to 16.3 hrs. based on July Z4 data taken at 1600 hra. (the most rapid oscillation recorded during my studies).

The extent to which piling up of surface waters occurred at the south end of the lake (now the leeward end) is seen in Fig.9 where the o 7.0 meter temperature reached a high of 23.3 e on the twenty-fourth at

1000 hrs. These observed results concur with Mortimer's findings and support his claims that moderate winds of some duration will enhance the , Temperature in DC 22 23 24 25

2

3

Depth in 5 Meters

6

7

8

Fig.10. Telliperature profiles at 3bP on July 21,22, and 24. Reinforcing north winds of the 2!lth pileJ warn, epililllnion waters at the south end. Isothermal conditions exist in the upper '+ meters of the water column on July22 due to surface turbulence caused by dampening south winds on this date.

VJ a 31. thermal stratification in a lake.

Morphological and Physical Effects

As mentioned earlier a seiche may be influenced by any of three mechanisms. The major jnfluence, the winds, have already been discussed.

The remaining two factors, morphology of the basin and frictional resistance between moving water masses. I found very difficult to discern.

The shallow conditions found at both ends of Lake Otsego should cause the period of an internal seiche to be slightly longer than pre­ dicted by eq.l, and may cause seiche dampening (ie. decrease in isotherm amplitude). Wetzel (1975) explains that any constriction which impedes the normal flow of water will serve to enhance the seiche period.

Enhancement of the periodicity occurs due to surface waters located over the shallows being effectively pooled there. Pooling does not permit maximum mixing of all surface waters, subsequently this will maintain the epilimnion (e) at a lesser depth than otherwise expected.

In turn this will produce a longer period than predicted.

I was unable to observe any of these consequences directly. How­ ever, 1 do feel that the basin morphology effected my findings of July

15. My inability to record more precisely the effects caused by the morphology of the lake was due to constantly changing wind conditions which are by far the prevalent influence on the internal seiche (Mortimer,

1952).

Coriolis effects on the internal seiche in Lake Otsego would be minimal due to the side constraints imposed by the east and west shore.

The lake basin being considerably longer than wide would greatly modify any rotational movement of the seiche (Wetzel,1975). Earlier findings indicating such a rotation (Harman,1982)jmay in fact be due to other 32. factors: 1) morphometric parameters, 2) difference in time required to tilt the thermocline in response to the internal seiche, and 3) changes in wind stress (Mortimer,1955).

Frictional resistance between water masses moving at different velocities results in a turbulent action which dampens the seiche.

Hutchinson (1957) states that turbulent viscosity can reduce a seiche a full 25% per cycle. Again because of the overriding dampening and reinforcing effect of the daily winds on the lake I was unable to monitor dampening due to frictional resistance alone. (I feel that three or four days of very calm winds would be required to discern this means of dampening). This is not to claim that frictional resistance does not exist. Such factors were considered in the computer model.

Flow in a Two Layered Basin

My study of the internal seiche and the flow of water associated with it indicates that the seiche is a major means of moving vast amounts of water in a lake, both vertically and horizontally. Further­ more the seiche may therefore be a major factor in the distribution of plankton in the lake.

Mortimer (1952) showed that a two layered system consisting of an epilimnion and a hypolimnion adequately describes most phenomena involved in the action of the internal seiche.

It should be recalled that the quantity of water displaced during the rocking motion of the internal seiche involves nearly the entire volume of the lake. As many have stated (Demoll,1921; Thomas,195l, and

Hutchinson,1967) movement of this water will undoubtedly alter the posi­ tion of planktonic organisms in the water. In relating a two layered model to Lake Otsego it is possible to determine the velocity at which 33~

the waters of the epilimnion and hypolimnion are being displaced in

response to the seiche.

The velocity of this water displacement can be calculated from

eqs. 3 and 4. Using the following mean values from Fig.ll we obtain: 4 e=7.0 meters, h=43.0 meters, 1=11.1 kID, s=8.0 X 10- (ie. 1.0 meters in . 4 1.25 km, the distance from 3MP to the node), T=18.6 hrs. (6.69 X 10 sec.).

Equations 3 and 4 yield nodal epilimnion and hypolimnion velocities

during a half cycle of the seiche as 0.103m/sec. and -O.016m/sec.

respectively. Therefore during one half cycle (3.345 X l04sec.) the

mean displacement of water moving past the node is 3445 meters of epil­

limnion waters and 535 meters of hypolimnion water. Due to turbulence

and mixing it would not be expected that each water molecule will return

to its original position during the following half cycle.

The absolute maximum horizontal velocity is attained when the

thermocline is level, the minimum horizontal velocity occurs when the

seiche is at greatest tilt. The values above are minimum nodal velocities

for a seiche with the parameters indicated. Maximum values can be

obtained by multiplying each by~/2 (ie. O.16m/sec. and -O.025m/sec. for

the epilimnion and hypolimnion respectively). Also horizontal velocity

is greatest at the node and decreases to zero at the basin ends. Con­

versely vertical velocities are greatest at the basin ends and zero at

the nodal point.

Ragotzkie and Bryson (1953) in their study of Daphnia pulex in

Lake Mendota stated that the zooplankton did not carryon any purposeful

horizontal movement. Furthermore Colebrook (1960) concluded that the horizontal distribution of zooplankton is determined by a large extent

'on the water movements. The internal seiche in Lake Otsego, which Length of Lake in km (as measured from North End) North South 1.1km 2.2km 3.3km 4.4km 5.5km 6.6km 7.7km 8.8km 9.9km 11.0 km • 3 mp -{ Om - ­ ------­ - - - 7m ­ - ­ -- 10m - - ­ - ­ - -

20m

t

h

30m

40m

50m

Fit',.ll. LOIl/..'oitu,linal cross sectioll of a lIIodell'd lake \~ith the sallie parameters found in Lake Otsego. Thl~ slope of the therlliocline is represented by (s). The thenllocline has a Illeall depth (20) of 7 meters. w po accounts for large scale water displacement, alters the distribution

of planktonic organisms in the lake. Prediction of the degree of re­

distribution of certain plankton in accordance with the internal seiche

in Lake Otsego follows~

The Modeled Redistribution of the Zooplankton Resulting from Interactions

with the Internal Seiche

Plankton populations in lakes have been reported by observers

Ragotzkie and Bryson (1953) and Smith (1975) to exhibit a spatial

heterogeneity. Smith (1975) states that biological and biochemical

factors may he partially responsible for the formation of accumulations

of plankton, however turbulent transport is the overriding factor in

establishing plankton distributions.

The effect of the internal seiche on the temporal and spatial

distribution of zooplankton in Lake Windermere was studied by Colebrook

(1960). Colebrook observed organism patchiness and attempted to explain

this phenomenon by considering the following: the effect of the uni­

nodal seiche alone, and the effect of the uninodal seiche in combination with diurnal vertical migration of zooplankton through the thermocline.

Colebrook reached two conclusions on the horizontal distribution of

zooplankton based on theoretical effects of water movements in a

stratified lake. Firstly that internal seiches should have a temporary

effect on zooplankton distribution. Secondly the effect of the internal

seiche combined with diurnal migration through the thermocline should

have a permanent effect on horizontal distribution.

Based on Colebrook's second conclusion Kamykowski (1978) investi­

gated the patchiness of zooplankton in Lake Windermere through the use

of a computer model. I have performed similar modeling techniques in an analysis of the effects of the internal seiche on zooplankton in Lake

Otsego. Following Kamykowski (1978) the basic assumptions are : a) wind

induced direct water movements (ie. surface waves, Langmuir currents, etc.) are ignored, b) Mortimer's (1952) two layered lake model suffi­ ciently describes the internal seiche, c) effects of diffusion are ignored, d) the initial distribution of organisms is uniform, e) zoo­ plankton behaviorisms contribute to the organisms vertical position

(ie. diurnal migration), and f) the zooplankton are capable of crossing the density barrier posed at the thermocline during their diurnal migration. These assumptions are based on the earlier works of Ragotzkie and Bryson (1953), Mortimer (1952), and Colebrook (1960).

Lake Otsego is modeled as a rectangular basin of uniform depth with a water column composed of bWO layers; the epilimnion and the hypo­ limnion. The error inherent in such a model was alluded to earlier.

The various parameters required in this model were derived from empirical data collected on the lake. Therefore the model projects a good approx­ imation of the internal seiche on Lake Otsego.

The initial position of the thermocline is slanted due to the wind piling waters at the leeward end (Fig.ld). When the wind stress ceases the seiche is initiated. In the following discussion the lake is assumed to be initially as shown in Fig.ld.

The basic equation describing the internal seiche wave is given byeq.l

l\.:: cT

The notations in the equations used to generate the computer model are as follows: 37.

C :II phase speed T ~ period of the internal seiche g ~ acceleration due to gravity

1'- :II wavelength h = depth of hypolimnion e = depth of epilimnion ph :II density of hypolimnion pe = density of epilimnion Ze thermocline depth a = amp Iitude

k :II wave number (ZU/?w) x = space variable eu wave frequency (LitIT) t = time variable Ue = epilimnion horizontal water velocity component We = epilimnion vertical water velocity component Uh = hypolimnion horizontal water velocity component Wh = hypolimnion vertical water velocity component z = depth variable D = % damp per period

The standing wave oscillating about a mid basin node at a depth Ze is given by

Ze :II e + a cos(kx)cos(cut) (7)

Kamykowski (1978) used the following equations to determine the horizontal and vertical components of velocity for a moving particle which was subjected to a seiche described by eq.7. The horizontal components of velocity are:

Ue =71 ae s in(kx) s in~t) (8) 4e

Uh = -d8C sin(kx)sin(Qt) (9) 4f1 while the vertical components are:

We :II -z aQcos(kx)sin~~t) (10) e

Wh = -(e+h+z) awcos(kx)sin(~) (11) h

Horizontal position of a water particle is dependent on changes in both

(x) and (t), that is Ue and Uh varies as (x) and (t) changes. Therefore the horizontal component of velocity is determined by taking the partial 38.

d Ze d Ze derivative of eq.7 with respect to (x) 0 x and (t)~ The vertical

velocity component varies only as (t) changes. The vertical components

are found by taking partial derivatives of eq.7 only with respect to 'd Ze (t)d t

In the epilimnion and the hypolimnion the horizontal components are reversed, as indicated by the difference in sign. Their magnitudes are inversely related to the corresponding layer thickness (e and h respectfully). Maximum horizontal displacement occurs when (kx) equals

riiJ/2 (sin(kx)=l), this occurs at the node. Similarly minimum horizontal velocity occurs at the basin extremes.

The vertical components witness a maximum at the thermocline (Ze) and decrease as they approach either the surface or the basin floor. The vertical velocity is maximized at the basin ends (ie. when (kx)=~: cos(kx)=l).

The model of Lake Otsego is based on seiche data typical of mid summer stratification. (It is important to remember that certain values

in the program are variables, and the values assigned to these variables are approximations representative of the lake conditions I observed during mid summer). The modeled Lake Otsego exhibits the following

parameters: 1= ll.lkm, e= 7.Om, h= 43.Om, a= 5.Om, which when substi­

tuted into eq.l produces a theoretical internal seiche period of 18.5 hours.

The model begins with the lake appearing as in Fig.ld and zoo­ plankton distributed uniformly across the lake (x axis). Simulations were performed in modeled one hour increments for 120 hours. The vertical position (z) of the zooplankton equals the sum of its swimming velocity and the vertical component of the water at its coordinate in the basin. The horizontal position (x) is dependent only on the horizontal component of the water motion (Ragotzkie ·and Bryson,1953). The zoo­ plankton is assumed to follow the classic migration pattern (Hutchinson,

1967) namely to swim do~nward in the water column for 12 hours starting at sunrise (0600 hrs.) then upward for 12 hours starting at sunset

(1800 hrs.). Naturally their movement is limited by the basin bottom and the surface, and such a limitation is incorporated into the model.

Figure 12 illustrates the change in horizontal position of a mid basin organism with a swimming rate of 4 meters per hour over a 120 hour period. In this simulation the seiche is initiated in synchrony with the onset of downward migration of the zooplankton at 0600 hours. The currents are such that the organism's horizontal position may be altered nearly 3km in 28 hours (eg. the period between 83 hrs. and III hrs.).

Given these conditions it can also be seen that the seiche serves to concentrate the organisms in the south end of the lake. The oscillatory nature of Fig.12 is not simple due to the fact that as the organism passes through the thermocline it enters a water mass moving in the opposite direction; a water mass which will, due to the activity of the seiche, also reverse its flow at regular intervals.

Similarly Fig.13 exhibits the vertical change in position of the organism. The organisms rate of decent and ascent appear in Fig.13 to be due solely to its swimming velocity and indeed this is the case since mid basin vertical currents are nearly zero.

Further simulations were conducted which considered organisms distributed uniformly across the lake. The surface of the modeled lake

(Fig.14) has been divided into tenths and a hypothetical organism with a diurnal migration rate of 4 meters per hour has been recorded at each Distance in BOpO.+ *32 Meters 222 from ** 2* 2:~:.~ :~2* ** 2- 2 NO.ih 2*2* *2 End ** of 6El33.+ * * Lake * * *2 * 232 * 2 2**2 r)... 2 2 2::~ * *2*3 * * 5667.+ 2 32* ~* *2 2* 2 2*** 'J •.'J *23-

4500. t +------+------+------t------+------+ O. 24. 48, 72. 96. 120. Time in Hours

Fig.12. Th~ horizontal coordinates of a diurnally vertically nligrat~ng mid basin zoo­ plankton monitored every 1.0 hr. for 120 hrs. Mid basin is approximately at.. 5550m. This projection was generated by the progra~l. the resolution is such that so~~ points can not be separated and so appear as 2 or 3.

.c­ o 4:t •

'** +0 ...... C':l ** I r'4 0­ !.-t o *'* '* I o '*'* I N ** I r·J* ** I I '* ** I '** I '* r·J ** +-0 *'* le- "* r·J I ** I *~ r·J* ** ** * ** ***** ** * ** '* *" ** r·J * **" * ** ** ! **** *" +0 '* * '"-' rJ * o ** ** c .....o ** I .u i ..... (/) * I o ** +~ c,. *** ! r·J * * ...... *** ell ell U \-i ** ** ..-/ ..c r·J * J-J 1-<0 *** ** (IN , ;:...... *" * I +0 + + .;­ + o o -0 r·J ~ M I 1 division (denoted as start position Ohrs. in Fig.14). The time of day is sunrise (0600 hrs.) and once again the seiche is synchronous with the onset of the downward migration. A view of the modeled lake surface

24 hours later reveals that the migrating zooplankton have returned to the surface as expected but that because of variations bestowed by the seiche their horizontal position is slightly askew from the original position. This projection is continued for six successive days. The overall effect appears as a concentration of organisms to the south end of the lake, also note that the organisms exhibiting the greatest change in position are the mid basin organisms. This is due to the fact that horizontal currents are at a maximum at the mid basin as predicted by eqs. 8 and 9. Similar simulations were performed under identical con­ ditions for organisms with vertical migration rates of la, 8, 3, and

1 meters per hour respectfully (Figs.lS-18). Worthington (1931) states that such migration rates are not uncommon among zooplankton.

Clearly the organisms least effected by the seiche action are those which migrate at the greatest speeds. The 10m/hr. organism (Fig.

15) maintains nearly its original position after six days. This animal spends only approximately five hours in actual migration before encoun­ tering the bottom or the surface (note the program is such that the organism does not become "stuck" on the bottom when maximum depth is attained but rather is still influenced by hypolimnion currents).

Organisms represented by velocities of 8, 4, 3, and 1 meter/hour

(Figs. 16, 14, 17, and 18) all exhibit the same general tendencies as those found in the 10m/hr. organism. All show concentrations of zoo­ plankton at the-south end, particularly at 120 hrs. Likewise at 72 hrs. all demonstrate a rebound effect, and shift northward. It is also 8.111(1 lenV'h In km hom the NOflh End .. 10 11

Sun 01 I ~ t ' ~ ~ : ~ • I TIme

Hours'n 241-----­ <...: :.. I

~ 481 .r. • ;I .. I U .. I

~2' r .L ~ 4 5 6 ,. •

96 r--­1 ~ ~ .:;r 6 •• • I

1201 I ~ oJ. ~ It 1 II 9!

II melin/hour

t Fi::;.l'.-lS. The ::-,'sults of [i,vC COI;l[lutcr 1Ilocll~1 rU:lS \o'hich arc iclcntical excE:;Jt fOl' or:::anisr\ swimming speed. The row in:lic.:ltes the lenGth of the lak2 in krd. inlL~rvals. Tlw follo....·ing ro....· inclL~atcs the initialopositiOl' of the evenly ,li:;tributed '::

0", w 44.

8nin J..enqtn in km 'rom rhq Norrh End

10 l'

Sto"

Time in Hours 24 4 7 8

48 8 9

n

96 45 78

45~ '20 1 m.twfhour Fig 15.

~n J..8n9th In km 'rom th4 North End

'0 '1

1 2 J 4 5 6 7 e 9 TIme on Hout> 4 , 2 J 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

~ 2 J 2 4 5 6 7 e 9 I

96 1 2 3 4 5 6 ) 8 9

120,~1 ....;.. ~__.:;...­ --.:; ;..-.-_:;,67;::8~9~

Fig 16. J rnelltrslhour 4-5.

Batin L~ in km from the North End Startlnq o '0 It

rome ,n Hours 24 4

48

n

96

120 Fig 17. 8 meter/hour

Bnin L~ in km trom 1M Norttr End 5,-, or-__-,'--- ....;. .;:... -,'--- -,:...... ;:... ..;.... -....;:- ;:- ~'O=----':;'~

0f---...,..---_....,...... ,...... ,... ,....­ .,-­ -:­ -..:;...... ; ~ r_ ,n Hovn 241­__...;...... ;:... --;. -'" .;­__~....:;..----;..._-----..::;....---.;._--___j

48r- .-- :;- --;'-- ~----_5;._---__;..6----..;....-----..::;....--_;9--___j

s nr---.,....----7-----....;.----.-7---..---7'------7-----7-----....:;...----7-.------4

!l6r----.....--..,.------;'------:"-----7-----....;...----;----_-----:=---__--:-__~

12O'---_...;...__ ~---J -7-- ---;=--- ..;. .;...... ;: ----;:...- ....;:__ y

Fig 18. 10 meter~/hour 46,

obvious that the magnitude of redistribution is indirectly related to

the organisms migration velocity, with the slower swimmers exhibiting

the greatest change in position.

Upon closer examination of the data it appears that the pattern of redistribution established in the first cycle of the seiche will pre­ dominate and be repeated inthefollowing days. In other terms, if the initial concentration is southward, that pattern will be maintained during the following days seiche activity although a rebound effect is apparent at 72 hrs. The overall trend is to concentrate organisms at the south end. The reasons for this are two fold. Firstly the inherent parameters of the internal seiche in Lake Otsego, namely the 18 hour seiche period. A seiche with a 12 hour period would of course produce a very different redistribution of organisms. Secondly and perhaps the more subtle is the fact that the horizontal velocity of the water is greatly reduced at the lakes extremes. An organism swept to either end of the lake can become virtually entrenched there. An organism with a migrating velocity of one meter per hour will be exposed to the initial epilimnion flow for a period of time ten times as long as an organism capable of 10 meter per hour migration. Many more of the slower swimming organisms will be swept by the relatively rapid mid basin horizontal currents to the leeward end of the lake, where they eventually sink below the thermocline and where they are subjected to only the very slight horizontal return currents. This seems to be in agreement with

C~lebrook's (1960) conclusion regarding the permanent effect on horizontal distribution bestowed by the internal seiche on zooplankton migrating through the thermocline. One might wonder why the entire population of zooplankton does not eventually become concentrated at the leeward 47.

end of the lake. There may be a number of interrelated reasons why this

is not the case.

I have already demonstrated that the fastest migrating organisms are capable of avoidin~ concentrations at the ends of the lake for the reasons discussed above. A second factor imposed on plankton distribution pertains to the onset time of the seiche (ie. when does it start rocking?).

In previous discussions the seiche was in phase with the diurnal migration of the zooplankton. The initiating winds however can stop at any time of the day to produce a seiche, while the diurnal migration remains linked to the flux of daylight.

Such a problem can be modeled if the program starting time is altered, that is continue to allow the modeled zooplankton to migrate down the water column starting at sunrise for 12 hours then back up again for 12 hours as before. However the seiche will be started at a different time and therefore at a different phase angle. In Figs. 19-22 a plankton with a 4 meter per hour migratory rate is subjected to a seiche with a phase angle of 0, r:f /2, r;1, 3~/2 respectively. This corresponds to a seiche initiation at sunrise, noon, sunset, and midnight respectively. Under these conditions the plankton exhibit opposing concentration patterns when the initiation time of the seiche is separated by 1800 or 12 hours.

As discussed in my introduction frictional influences induced on the thermocline by opposing movement of epi1imnion and hypolimnion waters acts to dampen the seiche. Throughout the summer of 1980 while collecting temperature data I was constantly searching for an amplitude change in the seiche which could be correlated with the dampening function. I was never able to detect a change in seiche amplitude 48.

BaSIO Length In km fram the North End

10 11

Stan 0 Time on Hour, 8 24

9 4S

5 72

2 9 96

- 1 '. 120 7 8 9

4 m«ten/hoor

Balm length in km from 11,. Nor1h End 10 11

Start

Time ;n Hours24\- ...;... ..;.- ---':'--- ..::- ::- ----'::-__---': ::- ;-__---1

721-_..;....._....;.. .:!--__~-----~----~------,;------'!------O---1

~61_--...;.--~'------;.....--..;..------.';.----~:....------;:....---....:;.-~

120 1 2

4 meteu/hour (phne ~lllJle r./21 Fig.19-22. The effect of the internal seiche on a 4m/hr. migrating zoo­ plankton. In each computer run the seiche is initiated a't a different phase ang:e. Phase angles of O,U12,i,and 3~/2 are out of phase by 0,6, 12, an~ 18 hrs. respectfully. 49.

BaSin Length In km from the North End

10 , 11

Start 0f--...;----;----;---~---....:;..---....:;..------:----.:;----;:.----___l Time

Hour$'" 24f-:---:---.,___-----;----;------:------~;__----__-----_:_------___l

48f-..;---;---~-----___;--.;:._------___;.------___;.----.::_----~----..,

72f--__.,...---___;=------~-----.,___--_:_------.....,__------_:_----;__--~;_____l

120LT1;:.2_...;;... -;-__---;=------;=------7 ~------_;_-----....J

4 rneten(hour Iphail angle IF) Fig 21.

Basm Length In km from the North End

10 '1

Stan I 01----,------,-----,-,-----,-----,---...... ,.----.,...----.,------,------1 Time

Hours'" 24f------c,------c------::------;-----.,___------,------:----;---:------..,

48r------,------,------.,___----~----.....,...---.....,...-----;__-__.,...----:--____i

72 01 .. 1

,:c. ....;. ....;;_.;;... ------,'-- -;- ....;... ---;.7...:8:--.:;.9_-!

4 meurrs/hour lphase angie 3- 1 21 Fig 22. 50 which I could not subsequently regard as being due to a change in

local wind direction or in wind force, a phenomenon which I found to be

rather common on Lake Otsego. Nevertheless the initiating wind which

has stored potential energy in the form of an amassment of warm epi­

limnion waters at the leeward end of the lake, will on the rebound

disrupt the density stratification of the thermocline and cause tur­

bulence (Hutchinson,1957). Therefore, though I could not detect this

dampening factor I fully believe it must exist, and in Figs. 23 and 24

a model of a 4 meter per hour migrating zooplankton is subjected to a

seiche with an incorporated 10% and 35% damp per cycle respectively.

The dampening function (eq.2) was applied to each period over the

course of the 120 hours. The 35% dampening value was selected as a maximum possible damp only because it represents the largest observed

dampening effect found in other similar lakes (Heaps and Ramsbottom,1966).

The 10% value represents an approximation which in my opinion is the

smallest dampening value which could be measured and not be confused with simple seiche perturbations.

As is to be expected as the dampening value is increased the

plankton concentrations become less and less obvious. The 10% damp

(Fig.23) demonstrates a similar distribution pattern of plankton to

that found in Fig.14 which shows the same modeled organism subjected to

zero dampening. The difference in these two projections appears as a restricted or hindered horizontal movement of the dampened organism.

Such a hindrance of horizontal movement is even more evident in Fig.24 which represents a 35% damp imposed on tre internal seiche, here very

little horizontal variation occurs. (Although the dampening function effects only the amplitude directly and would not appear to influence S1.

BoaSIC Length In km trom the North End 10 11

St.rt I

Time ,n Houn 241------+-----~------=------~---~------.;-----;.---:------';---1

I 4BI------;. ~-----.;_----;:._---~-----~------;:---.:;---;--1

I 72---.;..---...;:...------.:;------.:;-----c;------.....::;.---;...----.;:...---.;:...-----! g6\----:------=---~---=------"----~----::--1

120 I

4 mlltllrs/hour (10% damp)

Baltn Lenqth In K,," from the North End

10 11

Start T;m. o --.:, ---.:=-­ ;...... :;.. ~-----~-_---'----_---'!------~----__...j ,n Hourl 24 :_----....;...-----.;..------.:::....----.;.------::---~--~--..;._---J

72r------...:.....----~---....;.._------=:...----~--~----!--~---~-___J

96r-- --:..- ;...... __----=~ ____:;4:...... :.:L---~--~----__:_--~--.....;..--~

12"'- -...;. ~-----~---___..;-----~--::-----~-~--::.--l

4 metMs "hour 135% damp)

Fig.23,2(. Two Jifferent coreputer runs sujjecteJ to a 1 ;~~ and 3S~~ ~amp. The ~er~ent Jat1p shown represe~ts the ener;y loss iJer ~t.'rio,l 52· , f the horizontal position of the organism, in truth it does due to the i ! fact that in the equations which determine the horizontal coordinates

of a particle in the water (eqs.8 and 9) an amplitude function appears).

A fourth cause o~zooplankton concentrations appearing in an

enclosed body of stratified water is the continual modification of the

seiche by constantly altering wind conditions. Such an influence which

is related to the unpredictability of localized weather conditions can

not be accurately modeled. This mayor may not be a serious regression,

for light, brief breezes on the lake would only alter the position of

the near surface organisms. Theoretically these winds would be ineffec­

tive in altering the distribution of zooplankton during the daylight hours when they are presumably in hypolimnion waters. Conversely the

effect of very strong local winds of any duration could greatly alter

the distribution of the zooplankton. Mortimer (1952) has demonstrated

that moderate winds which steadily but slowly build to strong gale force winds can maintain the steady state condition, and would probably

force the initiation of a new seiche. However a sudden onset of a gale

force wind could greatly displace the thermocline and force a large scale mixing of epilimnion and hypolimnion waters, clearly this would cause a gross redistribution of zooplankton and present a very complex change in the dynamics of the water body.

Field Studies

Working on Lake Windermere Colebrook (1960) collected a series of

plankton samples and explored the effect of water movements on their

distribution. Using temperature and wind data Colebrook assessed the

nature of the water movements and determined that they should have a

large effect on the horizontal distribution of the zooplankton. 53.

Kamykowski (1978) used a computer simulation to represent the

effect of the internal seiche on zooplankton migration and distribution.

These simulations produced results which approximate Colebrook's empirical findings. Colebrook however, did not record the phase angle

(seiche initiation time) for his field data. This information was shown earlier to be very pertinent in predicting zooplankton distributions.

The correlation Kamykowski obtained between his computer model and

Colebrook's field results can not therefore be viewed with complete confidence.

In order to demonstrate the accuracy of the computer prediction one must monitor the seiche, determine its position at a given time and

then proceed to perform zooplankton collections and enumeration.

During August 1981, after my computer analysis was nearly completed I attempted to show empirically the relationship that the internal seiche in Lake Otsego had on the redistribution of zooplankton.

Prior to my field collections of zooplankton I monitored the seiche activity in Lake Otsego for a period of seven days (8/15/81 - 8/22/81).

During this time the seiche period was approximately 18 hours (17.6 hrs.).

A period of about 18 hours can probably be considered characteristic of the internal seiche during late summer stratification in Lake Otsego.

Surface zooplankton collections were made between 1900 hours and 2000 hours on 8/22 and 8/25. The parameters used in the computer model would permit only the fastest migrating zooplankton (8-10 meters per hour) to attain surface positions at this time. This was not the time when zooplankton numbers would have been at a maximum in surface waters.

However, the purpose of this investigation was to demonstrate a variation in the zooplankton flux in relation to seiche activity. Therefore 54·

recording of the zooplankton population when they were at their max­

imum was not necessary.

Prior to the collection of 8/22/81 temperature profiles of the

epilimnion and metalimnion were taken at points approximately 2km north

and south of the seiche node. These profiles indicated that at that

time the seiche was aligned in such a manner that the thermocline was

nearly parallel to the surface (Fig. If) .. Thermal profiles taken earlier

in the day indicated the phase angle of the seiche to be ~/2, ie. the

seiche was in the "start" position (Fig.ld) at noon. The seiche was

not necessarily initiated then, in fact it was not, rather it was in that

position as the result of previous rocking motion. Collections from both

the north and south stations produced zooplankton concentrations which 2 when subjected to X evaluation proved to be insignificantly different.

Three days later on 8/25 at 1800 hours the thermocline had shifted

by a phase angle of~/2 as witnessed by epilimnion and metalimnion

profiles. At 1800 hours on 8/25/81 the seiche was in a position

approaching that in Fig.lh.

Winds blowing from the southern quadrants were producing surface

turbulence, unfortunately no record of the magnitude of the wind was made at that time. These winds were buffeting the seiche induced

southerly flow of epilimnion waters. This hindrance of epilimnion flow

to the south did not apparently deter a zooplankton redistribution and

concentration at the south end. A definite concentration of zooplankton was found at the south end of the lake at this time. Meanwhile the

collection from the northern end of the lake was sparse. Statistical

analysis showed a significant difference in the concentration of plankton 2 at the north and south ends of the lake at this time (X = 3.09, P 0.10), 55 • indicating random distribution was unlikely and that some other factor was responsible for the deviation.

Many factors have been overlooked in the brief study. Despite this, I believe that the trends indicated in my sampling are evidence for seiche induced zooplankton patchiness, much as the computer model predicted. Furthermore, I theorize that the internal seiche is a major agent in causing redistribution of zooplankton in Lake Otsego.

Further work in this area of investigation should include the effects of such zooplankton population concentrations on the populations of the nekton (fishes) in the lake. One of the principal sport fish in

Lake Otsego is the ciscoe (Coregonus artedii) (MacWatters and Hill,1982).

This very popular game fish is a planktivore and appears to be associated with high concentrations of zooplankton (Harman,1982). It might prove interesting to monitor the correlation between areas of ciscoe fishing success and seiche caused zooplankton population concentrations. Date and time of temperature profile

6-23 6-24 6-24 6-24 6-25 6-26 6-26 6-26 6-26 6-27 6-27 6-27 6-30- 6-30 7-2 7-3 7-4 7-7 7-7 7-7 ~t:J~ri 0930 0930 H t1 1230 1500 1330 1000 1330 1600 2030 0600 0930 1330 1000 1300 1400 1530 1930 0930 1430 1800 ~ ~ , ;j Mn M 20.5 20.9 2]. 2 25.0 24.1 22.1 23.6 25.1 22.3 19.8 22,8 23.2 17 .6 18.7 20.8 23.4 21.4 20.2 23.4 21. 3 riN~ S 5 0 0 S10 S 5 S5 S 5 S10 a S 5 W 5 W 5 N 5 wl0 S 5 0 0 S5 NI0 0 HHW ZOI~ 0 17.5 17.4 19.2 17.3 20.6 19.3 19.8 20.0 19.0 L9.3 19.7 20.0 19.0 19.0 19.5 22.1 20.5 20.2 20.5 21. 3 0 ~Z2~ N.A 11. 3 19.0 17.0 N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. 52 ~ to< .j N.A. 17.0 18.5 16.4 N.I\. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. UJ ~ ><: ~d N.A. '16.7 17 .9 16.2 N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A .. N.A. N.A. N.A. N.A. N.A. N.A. N~ N.A. 16.3 16.6 16.1 N.A. N.A. N.A. N.A. N.A. w:» +'-0 N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. I<' t-' w t-,j. 5 16.2 16.1 15.6 16.0 17.3 1], L 17 .4 17 .5 17.5 17.6 17. 7 IB.O 17. 0 IB.l 18.0 19.6 19.B 19.1 19.7 19.7 5 +'-trl H 15.9 16.0 15.5 16.0 17.1 L6.9 o ..... t-' 17.3 17.2 17 .3 17. 3 17 .6 17 .4 L6. B 17.3 16.9 19.5 19.5 IB .5 18.9 19.4 0 '-OM 15.7 15.6 15. 1 15.9 16.9 16.B 16.6 16.9 16.9 16.6 17.2 17. 1 16.3 16.~ 16.4 18.1 18.4 18.2 17 .B 19.2 ZHm ~ 15.1 15.0 14.B 15.7 16.3 16.0 15.7 16.4 16.4 16.1 16.2 16.B 15.B 16.0 16.0 17.2 17 .4 17.0 16.0 18.2 Z 0 t:J '0 14.6 14.6 14.3 15.0 15.6 M t:J. ~ "d L4.9 14.9 15.B 16.2 14.5 15.4 15.4 14.7 15.1 15.1 16.4 16.5 16.2 14.9 L7. 2 ~H riM 10 12.7 1°.8 13.:> 1 ,.4 14.3 n~ 11.5 13.B 14.4 14.2 12.6 13.5 14.1 13.5 14.1 13.4 14.1 14.5 14.5 13.5 L4.7 10 ___ :r--z 11.2 L1.7 12.B 14.0 ::r: . ~ t:J 12.'1 11.0 12.1 13.3 12.7 L1. 6 12.1 13.1 12.'2 13.4 L2.2 13.1 12.4 12.0 12.B 11. 9 riHOH 9.7 10.7 11.B 12.9 10.2 10.1 10.9 11.B 11.3 10.6 10.5 12.0 LO.7 12.6 10.9 10.6 10.5 LO.2 12.5 10.6 (,)MZt-,j~ B.6 9.2 10.7 10.5 9.5 B.7 10.4 10.9 10.1 9.0 9.3 10.7 °J.6 10.3 10.6 9.1 9.5 9.5 11. 1 9.9 ~t:Jt:J B.O B.l 9.9 9.B 9.0 B.O 9.B 9.9 9.5 9.1 B.9 8.\1 9.1 9.4 10.4 B.3 8.9 8.6 LO.7 9.3 :r--<~H 15 7.7 7.7 9.0 B.9 B.4 7.6 9.1 9.0 9.3 B.7 8.5 8.7 B.6 9.1 9.B 7.7 8.2 8.0 9.9 8.B 15 ritrlM@ 7.5 7.1 B.3 B.2 B.l 7.4 B.4 B.7 9.0 B.O 7.9 -8.1 8.3 8.B '9.2 7.4 7.7 '-'" t-' Depth I 7.5 9.6 B.4 . HO in 7.3 6.9 7.6 7.8 7.7 7.2 B.2 B.l 8.5 7.2 7.4 B.O B.O B.3 B.7 7.2 7.3 7.2 9.0 8.0 trlno Meters 7.1 6.B 7.3 7.5 7.5 7.1 B.l 7.B B.3 7.0 7.1 7.7 7.7 B.o 8.4 7.0 7.1 7.2 8.7 7.9 Hri 7.0 6.6 :»~trl 7. 1 7.4 7.3 7.0 7.5 7.7 7.9 6.B 6.7 7.3 7.3 7.B 8.3 6.9 7.0 7.1 8.6 7.6 H tTl 20 6.9 6.5 6.7 7.1 7.1 6.B 7.2 7.5 7.7 6.5 6.5 6.9 7.1 7.3 8.0 6.7 6.9 6.9 B.l 7.1 20 ~g;g N.A. N.A. N.A. N.A. N.A. N.A. N.A, N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. St:J"j N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. .-.. ~ N.4. N.A. N.A. N.A. N.A. N.A. N.A. N,A. N.A. N.A. N.A. 'cJ N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N..A N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. I 25 6.3 6.1 6.1 6.4 6.5 :t 6.4 6.6 6.9 6.9 5.9 6.0 6.3 6.5 6.7 6.6 . 6.3 6.4 6.2 7.1 6.5 25 N.A. N.A. N.A. N.A N.A. N.A. N.A. N.A. N.A. N.A. N A. N.A. N.A. N.A. N.A. N.A. N.A. N.A •• N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. bl.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.4. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. ~.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. 30 5.8 5.3 5.4 5.B 6.2 6.1 6.0 6.2 6.2 5.4 5.5 5.B 6.2 6.4 6.1 5.8 6.0 5.8 6.8 6.0 30 N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N. A. N.A. N.A. N.A. 35 5.4 5.3 5.2 5.4 5.5 5.6 5.7 5.8 5.1 5.0 5.1 5.4 5.7 5.8 5.5 5.6 5.7 5.2 6.1 5.5 35

\~ Date and time of tomperature profile

7-8 7-8 7-8 7-8 7-9 7-9 7-9 7-9 7-9 7-10 7-10 7-10 7-ll 7-11 7-11 7-14 7-14 7-14 7-14 7-14 0930 1300 1600 2300 0500 0930 1230 1600 2000 0930 1230 1500 0730 0930 1430 0600 0900 1345 1900 2200

20.4 22.0 23.0 20.5 20.1 20.2 22.5 22.2 21.5 20.5 22.8 26.1 20.4 20.8 25.1 22.0 22.4 24.0 N.A. 25.2 510 N10 N5 0 S5 5 5 N10 N5 0 0 0 N 5 0 S5 515 S 5 5 5 S10 0 0

0 20.2 20.3 20.5 20.3 20.1 20.2 20.6 20.9 21.6 20.8 21.6 23.2 20.3 20.7 21.1 21.0 21.1 22.0 22.0 22.1 0 N.A. N.A. N.A. N.A. N.A. N.A. 20.5 20.9 21. 3 20.7 21.1 21. 7 20.1 20.6' 21.0 20.8 21.0 21.9 21.9 21.9 N.A. N.A. N.A. N.A. N.A. N.A. 20.1 20.6 20.6 20.5 20.8 21.1 19.9 20.4 20.9 20.8 20.8 21.0 21.8 21.7 N.A. N.A. N.A. N.A. N.A. N.A. 20.0 20.1 20.(, 20.1 20.7 20.8 19.9 20.2 20.5 20.4 20.8 20.8 21.1 21.3 N.A. N.A. N.A. N.A. N.A. N.A. 19.9 20.0 20.2 19.9 20.3 20.4 19.9 20.0 20.0 20.3 20.6 20.7 20.9 20.7 19.3 19.3 19.9 19.6 18.9 19.5 19.8 19.9 20.0 19.7 20.0 20.3 19.7 20.0 19.5 20.0 20.4 20.6 20.7 20.1 5 18.9 18.5 19.6 19.2 18.4 19.3 19.6 19.9 19.7 19.5 19.9 19.9 19.6 19.9 19.2 19.9 20.1 20.1 20.1 19.6 18.2 17.7 19.5 18.9 18.0 19.0 19.2 19.8 19.3 18.9 19.5 19.6 19.6 19.8 18.6 19.8 20.0 19.7 18.2 18.9 17.2 17.3 17.8 17.4 16.9 18.2 18.7 19.5 17.7 18.0 17 .6 18.3 18.2 18.5 17 .6 17 .8 17 .5 17 .5 17 .5 17. 3 16.1 15.9 17 .0 16.0 15.6 17 .0 16.2 17. 3 17.0 16.2 15.8 16.1 16.5 16.7 17. 1 16.3 15.9 16.4 16.4 16.0 10 14.7 14.9 15.7 14,8 14.6 14.5 15.4 15.8 15.2 14.6 14.7 15.0 15.0 15.2 13.6 15.0 14.7 15.7 14.0 14.2 10 12.1 13.2 14.4 13 .8 12.9 11.7 lJ .6 14.2 14.1 13.9 lJ.7 13 .9 13.4 13.7 12.9 13.5 13.4 14.2 13.3 12.9 10.0 12.4 12.9 12.0 11.2 10.7 12.4 12.8 11. 9 12.9 12.7 12.8 12.2 12.8 12.3 12.6 12.1 13.0 11.6 11.5 9.4 10.7 11. 2 10.8 9.9 10.0 11.0 11.4 10.9 12.0 12.1 11.8 11.0 11.7 11. 7 11.8 11.6 Depth 12.5 11. 1 11.0 in I 8.2 9.5 10.0 10.0 8.9 9.3 9.8 10.2 10.1 10.7 11.4 . 10.4 110.0 10.5 . 10.9 11.4 ll.5 12.1 10.0 10.0 Meters 15 7.8 8.0 9.6 9.6 8.2 8.9 9.2 9.6 9.9 10.0 11.0 9.6 9.5 9.6 10.0 11. 2 11.3 10.7 9.5 9.4 15 7.5 7.3 9.0 9.0 7.5 8.4 8.8 9.1 9.1 9.8 9.8 8.9 8.5 8.8 9.0 10.7 10.7 9.9 8.8 8.7 7.3 7.0 8.7 8.6 7.3 8.0 8.5 8.7 8.6 9.5 9.1 8.6 8.4 8.7 8.1 9.6 9.5 9.4 8.4 8.2 7.2 6.9 8.5 8.3 7.2 7.7 8.2 8.6 8.4 8.3 8.5 8.4 8.0 8.4 7.7 8.4 8.3 8.7 8.1 8.0 7.0 6.9 8.4 8.1 6.9 7.5 8.0 8.4 8.2 7.9 8.2 8.1 7.9 8.0 7.4 7.9 7.7 8.2 7.8 7.7 20 6.8 6.6 8.2 8.0 6.8 7.2 7.8 8.2 7.9 7.6 8.0 8.0 7.7 7.9 7.3 7.4 7.4 7.9 7.5 7.5 20 N.A. N.A. N.A. N.A. N.A. N.A. ~ .'6 8.0 7.9 7.3 7.7 7.7 7.3 7.7 7.1 7.2 7.2 7.6 7.4 7.2 N.A. N.A. N.A. N.A. N.A. N.A. 7.5 7.8 N.A. 7.2 7.6 7.4 7.1 7.4 7.0 7.0 6.9 7.3 7.2 7.0 N.A. N.A. N.A. N.A. N.A. N.A. 7.3 7.7 N.A. 7.1 ·.7.5 7.2 7.0 7.3 6.6 6.8 6.8 7.2 7.1 6.9 N.A. N.A. N.A. N.A. N.A. N.A. 7.1 7.7 7.7 7.1 7.4 7.1 6.9 7.1 6.4 6.7 6.7 7.1 6.9 6.9 25 6.2 6.6 7.0 7.2 6.2 6.6 7.0 7.6 7.6 7.0 7.3 6.9 6.8 7.0 6.3 6.5 6.6 6.8 6.7 6.9 25 N.A. N.A. N.A. N.A. N.A. N.A. 6.9 7.5 7.4 7.0 7.2 6.8 6.7 6.8 6.2 6.4 6.4 6.7 6.6 6.6 N.A. N.A. N.A. N.A. N.A. N.A. 6.8 7.3 7.2 6.9 7.1 6.7 6.5 6.7 6.1 6.4 6.2 6.6 6.5 6.4 N.A. N.A. N.A. N.A. N.A. N.A. 6.7 7.0 6.9 6.8 6.9 6.5 6.3 6.5 6.0 6.2 6.0 6.5 6.4 6.4 N.A. N.A. N.A. N.A. N.A. N.A. 6.6 6.8 N.A. 6.5 6.8 6.4 6.3 6.5 5.9 6.'1 5.8 6.4 6.2 6.1 30 5.7 5.6 6.4 6.5 5.8 6.1 6.5 6.7 6.8 6.4 6.5 6.3 6.2 6.4 5.7 6.8 5.8 6.3 6.1 6.0 30 N.A. N.A. N.A. N.A. N.A. N.A. 6.5 6.6 6.5 6.3 6.4 6.0 6.1 6.3 5.6 5.7 5.7 6.2 6.0 5.8 N.A. N.A. N.A. N.A. N.A. N.A. 6.4 6.4 N.A. 6.3 6.2 5.8 5.9 6.1 5.5 5.6 5.6 6.1 5.9 5.8 N.A. N.A. N.A. N.A. N.A. N.A. 6.4 6.3 6.3 6.3 6.0 5.7 5.7 5.9 5.4 5.6 5.4 6.0 5.9 5.8 N.A. N.A. N.A. N.A. N.A. N.A. 6.1 6.3 6.2 6.3 5.9 5.7 5.5 5.7 5.3 5.5 5.4 5.9 5.7 5.7 35 5.3 5.2 5.8 5.9 5.3 5.7 5.9 6.2 6.2 6.3 5.9 5.7 5.4 5.6 5.3 5.5 5.4 5.7 5.6 5.7 35

~

~" <,"r"'''''''' """"r."""'.('"'1A1lI' lw ii&lf.;;"J'fl."G1.,",·--..:'.·~...... ~~,!"7," .~. ~,""",~·t..,,,,,ToI~~"~'·''''~'i-\~'~l'~'fl'''I;lO':(''':, ll~XJiI""""'l'i"'-'" Date and time of temperature profile

7-15 7-15 7-15 7-16 7-16 7-16 7-16 7-17 7-17 7-18 7-18 7-21 7-21 7-21 7-22 7-22 7-22 7-22 7-23 7-23 7-24 '''';24 7-24 0945 1330 2000 0600 1000 1345 1630 0930 1430 1000 1430 0930 1600 2000 1000 1230 1600 2000 1000 1400 1130 1630 2015

23.8 25.0 26.0 22.5 23.5 27.0 25.4 23.4 25.9 22.2 24.5 25.7 25.8 25.7 23.2 23.2 23.5 23.6 23.4 23.7 23.4 H.A. 20.8 SIS SIS S 5 S 5 S 5 SID 0 S5 S10 N 5 0 0 0 0 S10 S20 S20 S25 S10 0 H2O HIS 0

0 21.0 20.8 20.9 21.0 21.3 21.9 22.0 22.0 22.0 22.1 23.6 23.3 23.5 23.4 23.3 22.9 22.8 23.0 22.8 23.0 23.3 24.1 23.4 0 21.0 20.8 20.8 20.8 21.1 21.6 21.7 22.0 21.9 22 .1 23.5 23.2 23.2 23.i 23.0 2?.9 22.8 23.0 22.8 23.0 23.3 24.1 23.4 20.9 20.7 20.5 20.7 21.0 21.4 21.6 21.7 21.8 22.1 23,/, 23.2 22.5 22.8 22.9 22.9 2?.8 23.0 22.8 22 .9 23.2 24.0 23.5 20.8 20.7 20.3 20.4 20.9 21.1 21.4 21.5 21.7 22.0 22.6 23.2 22.1 22.6 22.7 22.9 22.8 23.0 22.5 22.9 23.1 23.8 23.5 20.7 20.7 20.0 20.2 20.9 21. 1 21.3 21.1 21.5 22.0 22.3 23.2 21. 7 22.0 22.5 22.6 22.8 23.0 22.2 22.5 23.0 23.7 23.4 20.6 19.6 19.8 19.9 20.8 21. 0 21.1 20.6 20.9 21. 'I 2?. ? 22.8 21.3 21.6 22.4 22.0 21.9 22.5 21. 9 2?3 23.0 23.5 23.4 5 20.4 19.2 19.6 19.4 -:'0.7 20.8 21.0 20.3 20.7 21. 7 21.6 22.7 20.8 21.2 71.5 21.1 21. 2 22.3 21.4 22. 1 22.9 23.4 23.3 19.6 18.8 19.5 18.7 20.3 20.4 20.8 20.2 20.7 21. 7 21.1 22.6 20.6 20.6 20.8 20.7 20.5 2?2 20.4 22.0 22.4 23.3 22.4 18.117.5 18.0 17 .5 18.8 18.8 20.2 18.3 19.3 20.3 20.9 21.3 18.6 19.1 19.5 19.6 19.0 19.1 18.8 20.0 20.0 22.5 20.6 17.0 16.0 16.3 15.9 li.4 17 .0 18.0 15.0 17.4 18.5 18.1 17.2 16.1 16.9 17.7 17.6 16.7 16.9 16.3 18.2 17 . 1 18.5 16.2 10 14.7 14.0 14.7 14.3 15.6 15.7 15.9 14.0 15.1 13.5 15.8 14.3 15.0 15.3 15.4 16.1 15.2 15.5 15.1 16.5 14.4 15.8 14.6 10 13.5 12.2 13 .1 12.7 13.1 12. 1 11. 3 12.9 13.6 12.3 13 .1 12.6 13.2 13.2 13.4 14.4 13.5 13.8 13.8 14.2 13.5 14.8 13.2 11.9 10.6 11.9 11.4 11. 5 10.5 10.4 11.8 11.9 11.7 11.7 11.7 12.3 12.0 12.3 12.8 12.2 12.8 12.9 12.9 12.6 13.4 11.4 11.2 12.5 10.0 10.7 9.5 11.5 10.8 10.3 9.4 9.6 10.5 11. 1 10.3 11.2. 11.2r 11.1 11.0 11.3 10.8 11. 2 11.9 11.9 11. 7 9.3 8.9 10.9 10.1 9.4 9.0 9.4 9.9 10.0 9.4 10.6 10.6 10.2 10.4 9.8 9.5 10.4 10.6 11.0 11.0 10.5 11.9 9.5 15 8.7 8.6 10 .5 9.4 9.0 8.6 9.0 9.3 9.3 8.9 9.6 10.2 9.4 9.3 8.8 8.6 9.2 9.5 10.3 9.9 10.2 11.2 9.0 15 9.6 10.2 Depili \ 8.4 8.4 9.6 8.5 8.6 8.4 8.7 8.6 9.1 8.4 8.3 10.0 8.5 8.8 8.0 8.1 8.7 8.9 9.4 9.3 8.7 in 8.1 8.1 9.0 8.0 8.5 8.1 8.3 8.1 8.8 8.2 7.9 9.4 8.1 8.3 7.4 7.9 8.1 8.1 8.5 9.0 9.2 9.7 8.4 Meters 7.8 7.9 8.4 7.9 8.3 7.9 8.0 7.7 8.6 8.1 7.6 9.2 7.8 7.7 7.1 7.6 7.7 7.7 8.1 8.2 8.6 9.4 8.2 7.6 7.7 7.9 7.6 8.1 7.7 7.8 7.3 8.4 8.0 7.5 8.9 7.7 7.4 6.8 7.3 7.4 7.3 7.7 7.7 8.4 8.8 7.9 8.1 8.5 7.7 20 7.4 7.4 7.7 7.5 7.8 7.5 7,6 7.0 8.1 7.5 7.3 8.6 7.1 7.2 6.7 "1'0_ 0 -; • I. 7. 1 7.1 7.3 20 7.3 7.3 7.3 7.1 7.5 7.3 "'].5 6.9 7.9 7.3 7.2 8.4 6.9 7.u 6.6 7.0 6.9 7.0 7.0 7.0 7.8 8.2 7.5 7.2 7.2 7.1 6.9 7.3 7.2 7.2 6.9 7.7 7.1 7.0 8.4 6.9 7.0 6.5 6.9 6.8 6.9 6.9 6.7 7.7 7.9 7.3 7.0 7.1 7.0 6.8 7.2 7.1 7.0 6.7 7.5 6.8 6.7 8.3 6.7 6.9 6.4 6.7 6.7 6.8 6.9 6.7 7.5 7.7 7.1 6.9 6.9 6.8 6.6 7.1 6.8 6.9 6.6 7.4 6.7 6.6 8.1 6.6 6.7 6.4 6.6 6.5 6.7 6.8 6.7 7.4 7.5 7.0 25 6.8 6.8 6.7 6.6 7.0 6.7 6.8 6.4 7.3 6.4 6.6 7.9 6.4 6.4 6.4 6.5 6.4 6.5 6.8 6.5 7.2 7.3 6.9 25 6.7 6.7 6.6 6.6 6.9 6.6 6.7 6.4 7.0 6.2 6.5 7.8 6.2 6.3 6.2 6.5 6.3 6.4 6.6 6.5 7.0 7.2 6.8 6.6 6.5 6.6 6.6 6.7 6.5 6.5 6.4 6.9 6.0 6.4 7.6 6.2 6.2 6.1 6.4 6.3 6.2 6.4 6.4 6.9 7.1 6.7 6.4 6.4 6.4 6.5 6.5 6.4 6.4 6.3 6.7 5.9 6.4 7.5 6.2 6.2 6.0 6.3 6.2 6.1 6.4 6.4 6.8 6.8 6.5 6.4 6.2 6.3 6.5 6.5 6.3 6.3 6.2 6.6 5.8 ~.3 7.3 6.2 6.1 6.0 6.2 6.0 6.0 6.3 6.2 6.7 6.7 6.3 30 6.3 6.2 6.2 6.4 6.4 6.2 6.1 6.0 6.5 5.8 6.3 7.2 6.1 6.1 6.0 6.1 5.8 6.0 6.2 6.2 6.6 6.6 6.1 30 6.1 6.1 6.0 6.2 6.3 6.1 6.1 5.8 6.4 5.7 6.2 7.1 6.0 6.1 5.9 6.0 5.8 5.9 6.0 6.0 6.5 6.6 5.9 6.0 6.0 5.9 6.2 6.2 6.0 6.0 5.7 6.3 5.7 6.2 7.0 5.9 6.0 5.8 5.9 5.7 5.8 5.9 5.9 6.4 6.4 5.7 6.0 5.9 5.9 6.1 6.0 5.9 5.9 5.6 6.2 5.7 6.1 6.9 5.9 5.9 5.6 5.9 5.6 5.8 5.9 5.9 6.3 6.2 5.6 6.0 5.8 5.7 6.0 6.0 5.8 5.8 5.5 6.0 5.6 6.1 6.7 5.8 5.9 5.6 5.7 5.6 5.7 5.8 5.7 6.1 6.1 5.6 35 5.9 5.7 5.7 6.0 6.0 5.8 5.8 5.5 5.7 5.6 6.0 9.6 5.8 5.8 5.6 \ 5.8 5.5 5.7 5.7 5.7 6.0 6.1 5.6 35

VI co u.

APPENDIX II COhPUTER PROGRAH USED TO S IHULATE ZOOPLA~"KTON INTEP~CTION "nTH THE niTERNAL SEICHE.

C**************************************************************f*' C* THIS PROGRAH WAS WRITTEN BY JAMES HILL FOR THE C* STATE UNIVERSITY OF NEW YORK COLLEGE AT ONEONTA. C* JUNE 1981. C* ABOVE CONTROL CARD IS NECESSARY FOR BURROUGHS B6800 C* FILE EQUATION STATEMENT ALSO NECESSARY FOR 6800. C* CODING OF PROGRM1 DONE BY JAMES GREENBERG ACADEMIC C* PROGRAMMER ANALYST SUCO COMPUTER SERVICES CENTER. C**I****_.**********************.***.***.**.**••********.********* FILE 7(KIND=DISK,TITLE="HILL/OUTPUT.",MAXRECSIZE=22) REAL K DATA CHA/"*"I ST=O. WE=O. UE=O. K=O. C' C' READ IN INITIAL VALUES C* READ/,Z,X,SPEED 5 PRINT/,"PLEASE ENTER A,B,C,D" READ/,A,B,C,D WRITE(7,100)ST,X,Z 100 FORMAT(1X,3F10.0) 10 K=K+1 c* c* CHECK FOR TERMINATION, AND PROPER EQUATIONS C* IF (K.GT.12) GO TO 40 15 IF (ST.GE.120) GO TO 30 IF (Z.GT.7) GO TO 20 C* C* USE THESE EQUATIONS IF DEPTH < OR :: TO 7 C* Z=WE+SPEED+Z IF(Z.LT.O) z::o ST=ST+1. UE=A * SIN(.00028*x) * SIN(.339 • ST) WE=B * Z * COS(.00028 * x) * SIN(.339*ST) X=UE+X WRITE(7,100)ST,X,Z GO TO 10 ~o.

C' C* USE THESE SET OF EQUATIONS IF DEPTH ) 7 C* 20 Z=WH+SPEED+Z IF(Z.GT.50) Z=50 ST=ST+ 1. UH=C*SIN(.0002S*X)*SIN(.339*ST) WH=-(1.17+.024*Z)*D*COS(.00028*X)*SIN(.339*ST) X=UH+X WRITE(7,100)ST,X,Z GO TO 10 C' C' CHANGE SPEED EVERY 12 HOURS. C' /~ 40 SPEED=SPEED*(-1) K=1. GO TO 15 GO TO 5 30 CLOSE(7,DISP=CRUNCH) .STOP END Literature Cited

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