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The effects of power plant condenser cooling water entrainment on the amphipod. Gammarus sp.
I.tloer Re~.arch Vo! ~. p p 9:t? Io "~45 Pergamon Pres~. lu74 Printed ,n (ir~.al Hr,tam
THE EFFECTS OF POWER PLANT CONDENSER COOLING WATER ENTRAINMENT O'N THE AMPHIPOD. GAMMARUS sp. T~to,s~s C. Gtxg, WILLIAMT. WALLERand GERALDJ. LAUER New York University Medical Center, Laboratory for Environmental Studies. 550 First Avenue. New York 10016. U.S.A. (Receired 20 May 19741 Abstract--The abundant Hudson River amphipod Gammarus.sp. was examined for viability before and during entrainment in the Indian Point cooling water system. The mean per cent survivial of Gummarus sp. sampled during AT's of 7.1-8.3°C and ambient temperatures of 24.9-26.0 C was 98.5 and 97.4 per cent for the two intake stations and 90.1 and 96.8 per cent for the discharge canal stations D- 1 and D-2 respectively. A statisticaU.,, significant I:t ,= 0.05) difference was detected between the survivial of Gammarus sp. at the intake stations and di~harge station D-I, located near the upper end of the di~harge canal. Entrained Gammarus sp. experience increased initial and latent mortalities during periods of condenser chlorination. Comparison of the abundances of entrained Gammarus sp. during day and night sampling periods reveals a significantly higher occurrence during darkness. Temperature bioassays indicate that the thermal tolerance of Gummarus sp. is dependent on exposure time and ambient temperature. The temperature resulting in a 50 per cent mortality of Gammarus sp. for 30 rain exposure times, increased approximately I 1 C as ambient temperatures increased from 2.5 to 25.8"C. Consequently. GammuJ'ussp. was capable of surviving A'l-s of greater magnitude as the ambient temperature to which they were acclimated decreased. Temperature bioassays indicated that Gammarus sp. should be able to tolerate all projected time-temperature exposure combinations encountered during entrainment through the cooling water system.
INTRODUCTION
The purpose of this study was to determine the effects of condenser cooling water entrainment on the estuarine amphipod. Gammarus sp. This was done by laboratory thermal tolerance tests and by comparing the conditions of Ga~mnarus sp. taken from the plant's cooling water intake and from the discharge canal. This research is part o f a 5-yr program of studies of the Hudson River estuar~ begun in 1969 and supported b) Consolidated Edison Company of New York. Three research organizations are primarily involved in the overall study p r o v a m : New York University Medical Center, Laboratory for Environmental Studies is investigating plant operation effects on nonscreenable organisms: Texas Instruments Incorporated is studying effects on screenable organisms; Q u i r e Lawler and Matusky Engineers is developing a mathematical model for predicting ent~inment effects on striped bass populations. Gamntarus sp. is the most abundant species among the macroinvertebrate zooplankton entrained at Consolidated Edison's Indian Point nuclear power plant on the Hudson River estuary (NYU Medical Center, 1973). This amphipod is the major food orDnism of juvenile ( < 150 mm) striped bass. Morone saxatilis, in w.g. 8'11--F
the Hudson River and is also an important "food organism for adult and juvenile white perch .Xloro,e americana tTexas Instruments. 19721. Gam,~srus sp. appears morphologioally similar to G. tigrinus: however. ~an overlap of characteristics, especially in the juvenile stages, between G. ti.qrmux and G. daiheri makes exact species identification dil?icult (Bousfield. 19691. Due-to the extremel.v large number of organisms collected, no identification beyond Gamngtrtts sp. was attempted. Few studies on the survivial of entrained zooplankton have been reported. Markowski (1959) indicated that several zooplankton species, including gammarid amphipods, were able to survive passage through the condenser cooling system of a steam electric station. However, that report lacked quantitative information on ambient temperature. AT and chlorination. Kelly (1971) observed a 65 per cent mortality of entrained Neomysis awatschensis at discharge temperatures exceeding 90¢F. Mortality was less than 10 per cent at discharge temperatures from 80 to 86:F, which agreed with Kelly's laboratory temperature tolerance experiments. Heinle (19.69) reported up to 100 per cent mortality of entrained eggs and early nauplii of Acartia tonsa, although discharge temperatures were below the 937
938
T.C. GINN. WILLIA~,IT. WALLERand GERALDJ. LAL:ER
laboratory-predicted tolerance limits. A subsequent analysis (Heinle, personal communication)indicates that the high mortalities were associated with periods of condenser chlorination, lcanberry and Adams (1973) reported a mean mortality difference between intake and discharge zooplankton samples of 5.97 per cent. Discharge temperatures ringed from 48.6 to 85.0':F. There was no apparent difference in 24h delayed mortalities between intake and disc,barge samples maintained in ambient water baths.
MATERIALS'AND METHODS All tests were conducted at the Indian Point plant, which ison the Hudson River estuary at mile 43 above
the Battery. When operating at its rated capacity of 265 MWe, the plant's Unit I has a cooling water demand of approximately 280,000gal rain-t. The design AT is 7.2~C. Water enters the condenser cooling system through four shorelide intakes and is discharged in a 300 m long canal that will also be used by Units 2 and 3. The discharge canal terminates in a sub-surface diffuser system(see Fig. l). When Unit l is operating alone, the time of water travel from the Unit I condenser to diffuser outfalls ranges from 32 to 53 min, depending on flow. The transit time of water from the condensers to the discharge ports will be reduced to as little as 6-9.5 rain by increased flows during multiunit operation. (Con~iidated Edison Company at New York. 1973). After exit from the diffuser ports the AT of the discharge, when only Unit I is operating, is reduced by dilution to 50 per cent in less than 2 s and 95 per cent in 20 s. The dilution rate would be considerably slower during multi-unit operation.
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Laboratory thermal tolerance test Gammur,ts sp. for laboratory temperature-tolerance tests were collected using 500 ~m mesh plankton nets which were 0.5 m din and 2 m long. A 90 x 230 mm PVC bucket with a lateral 500 lu'n screened opening (63 x I(X)ram) was attached to the codend of the net. Test organisms were collected from the plant intakes and maintained in ambient temperature baths for 48 h before thermal tolerance experiments. Each test group consisted of 25 organisms which were selected to approximate the size composition of the river population of Gammarus sp. at the time samples were taken. Test organisms were sorted into [25-ml methylpentene polymer containers with bottoms of 500/tm mesh nylon netting. To obtain thermal exposures of desired temperatures and durations test containers with Gammarus sp. were immersed in constant-temperature water baths filled with aerated Hudson River water. Temperature was monitored continuously with a thermister telethermometer. At the end of the selected exposure time the test containers were immediately transferred to an ambient temperature bath. The instantaneous drop to ambient temperature, following exposure to elevated temperature, was designed to approximately simulate the thermal regime at the Indian Point submerged discharge ports. Control groups of Gammaru.s sp. were placed in the test containers and maintained at ambient temperature. Test organisms were examined for viability l h after thermal exposure. During summer ambient temperatures, test organisms were held at ambient temperature in the laboratory for examination 24 h after thermal tolerance tests. Organisms lacking pteopodal movement were classified as dead. Other behavioral characteristics, such as
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Fig. I. Schematic of the Indian Point cooling water system.
I'owcr plant condenser cooling locomotor abilit.~, stimulus respond, and spatial orientation were also noted throughout the tests.
Intake and discharge canal ,~mpling Samples of Gammarus sp. were collected on two dates each week (one day. one night) from 27 June to 24 August, at which time the day sampling was discontinued and onl) night samples were collected until 26 September. Collections were made at two of the Unit I intake bays(l-I and ]-2). in the discharge canal near its exits from the plant (D-I)and just prior to the first submerged diffu~r port (D-2)(Fig. It. Samples were taken at the surface, mid-depth, and bottom at each station, with nets of the type already discussed. Surface samples were collected by lowering a heavilyweighted net from a platform located over each station. M id-depth and bottom samples were collected by nets mounted on rigid PVC frames which were lowered to the desired depth on a vertical track. A total of 428 samples containing 59.602 Gammarus sp. were collected during the stud) period. Only samples containing more than five organisms (307 samples) were used for viability analysis. Since an air-curtain bubbler system was normally in operation at l-I. only I-2 samples were used for intake abundance estimates. Sampling time was normally 5rain: however, increased zooplankton densities occasionally required a reduction of sampling time to I rain. Collections were immediatel) transported to the laboratory at the plant and maintained in an ambient water table during examination. Collected organisms were classified as alive, stunned or dead by the same person throughout the study period. Stunned Gammarus sp. displayed little response to probing stimuli and reduced locomotor activity. Any dead or stunned organisms were immediately enumerated and removed from the sample. The collection was then preserved in 10",, formalin and the remainder of the organisms were counted later. Samples were collected before and during chlorination on each date. Sodium hypochlorite was injected into the cooling water prior to the intake pumps at a pre-arranged time. Normal chlorination procedure called for the addition of chlorine for 30 min to only one of the two circulating pumps at a time. Consequently, only 50 per cent of the cooling water flow received a chlorine injection prior to the confluence of the condenser water boxes at "the discharge canal. Beyond this point water from the chlorinated pump mixes with the flow from the untreated pump, resulting in a 1: I dilution of the chlorinated water in the discharge canal. Mean total chlorine residuals measured by the amperometric method at the water box and in the discharge canal were approximately 0.29 mg 1-J and 0.11 mg l-~, respectively. Groups of alive and
93,~
stunned Ganmvarus sp. were selected from intake and discharge samples and examined for viability 4,~ h after collection. The organisms were maintained in aerated HkJdson River water at ambient temperature. Amdysis of t'ariance Statistical analyses of Gammarus sp. abundance followed the method of Sokal and Rohlf(1909) for factorial analysis of variance with balanced design. Eleven night sampling dates and 6 day sampling dates were .~[ected for three way analyses of variance, i.e. for depth (surface. mid-depth and bottomL station (intake. D-I and D-2L and date. The abundances were transformed by Iog,ox + I to make the data conform to the assumption of homogeneity of variances. Differences between means of an). significant factor in the overall analysis were examined b) the Student-Newman Keuls procedure.
R ESU LTS
Temperature tolerance Gammarus sp. display pronounced seasonal variations in acute thermal tolerance, corresponding with changes in ambient river temperature. Temperaturesurvival curves for 30-rain exposures over an ambient temperature range of 2.5--25.8~C arc presented in Fig. 2. Figures 3 and 4 represent the relationship between 50 and 95 per cent tolerance limits (derived from logprobit analysis) and ambient temperature. These tolerances are the temperatures which result in projected survival of 50 and 95 per cent of exposed organisms. These data indicate that Gummarus sp. can tolerate about an I I C higher temperature during summer ambient temperatures than in winter. Once lethal
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Fig. 4. 95"° Temperature tolerance limits for Gammarus sp,
exposure temperatures are reached, the mortality response of Gammarus sp. is pronounced, since the TL~,, values are generally less than 2:C higher than the TL~.~'s. Exposure time was found to be an important factor in the response of Gammarus sp. to thermal shock. During most of the year. the test organisms could tolerate approximately 1.5-2.0°C higher temperatures for 5 rain than for 60rain (Fig. 3. 4 a n d 5). The test organisms also tolerated considerably higher temperatures during short-term exposures (5-60 rain) when compared with a '48-h exposure time (Fig. 4). The 60rain tolerance Iimits were approximately 5°C higher than the 48-h tolerance limits at an ambient temperature near 25"C. At an ambient of 25"C Gammarus sp. exposed for 5-60 rain to test temperatffres up to 35:C sur,,ived the full observation time of 24 h. However. 24-h survisal rapidly decreases as test temperature increase above 37°C (Table I). During sub-lethal temperature exposures, the test organisms were generally hyperactive. As test temperatures approach to within about 2~'C of the 60min
TL,,,. a pronounced shock reaction was noted as the test groups were returned to ambient temperature. Although hyperactive in the temperature bath. the organisms immediately lost orientation and mobility for periods of up to 0.5 h after return to ambient temperature. When exposed to lethal temperatures, test organisms generally displayed an almost instantaneous loss of mobility. Some isolated darting occurred during the exposure, but most test organisms were disoriented and unresponsive. This reaction was observed throughout the ambient temperature range at exposure temperatures exceeding the 60-rain TL,,,. The temperature which produces this stunned effect is usually referred to as the critical thermal maximum.
Intake-discltarqe riability The condition of GammamJs sp. collected in 307 samples at Indian Point Unit I is presented in Table 2. The mean per cent alive exceeded 90 per cent at all stations except during periods of condenser chlorination. The mean percentage alive and their 95 per cent confidence intervals at each station during all plant operational
Table 1. Latent mortality of thermally shocked Gammarus sp. at ambient temperatures of 24.7-25.8 C
Test temperature (°C) 33.0 34.2 35.6 37.0 37.5 37.8 38.3 38.9
5 0 0 2 0 0 0 14 100
Per cent mortality of organisms surviving initial thermal shock Exposure time Imin) ~5 30 60 0 0 0 .I 9 0 40 .
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0 0 0 92 90 --.
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Organisms surviving initial 5-60 minute thermal shocks were returned to ambient temperature and examined for mortality 24 h later.
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T. C. Gl.xx. WILLIAX!T. WALLERand GERAL,DJ. LALI.~
942
Table 3. Abundance of Gammarus sp. collected at Indian Point Unit I Iogto of N o I000 m - 3 Day Night ( 13 July- 17 August~ t I I July- 19 Septcrnber~
Station
Intake
2.641 ( Z 0.4631" 2.042 (+0.318) I. 167 ( _ 0.6301 3.223 ~__.0.521 ) 2.784 ( ± 0.629)
D- I D-2 D-I during chlorination D-2 during chlorination
3.858 I ± 0.253t 3.375 (_+0.2711 34"/5 I ± 0.283) 4.2(11 i ~ 0.2571 4.31 I _ 0.256)
* 950; Confidence limits of the mean conditions were: Intake. 96.9 + 0.76; D-I. 9..2.1 +_ 2.37: D-Z 95.3 + 1.87; D-I chlorination. 54.6 + 7.96: and D-2 chlorination. 74.9 + 8.49. Analysis of variance was not conducted on the survival of entrained Gammarus sp. since no adequate normalizing and/or variance stabilizing tran,h>rmation was found. However, a r*-test which assumes unequal variances (Welch, 1947) indicates a significant reduction in survival at station D-I when compared with the intakes during theperiod of maximum AT's (7.1-8.3"C). The survival at station D-2 was not different from ,ntake survival. Significant reduct;ons in survival were indicated during periods of condenser chlorination at both discharge stations. The per cent alive was lowest at station D-I during the full AT range of 4.4--8.3 C. Approximately 50 per cent of the Gammarus sp. in the samples were alive, the remaining 50 per cent were almost equally divided among dead and stunned categories. Groups of alive Gammarus sp. captured in the discharge canal during plant operation displayed no
latent mortality when compared with intake control samples during the 48 h observation period after collection (Table 4). However. approximately 75 per cent of the stunned organisms collected in the discharge canal during chlorination died within 48 h. The pronounced latent mortality of those Gdmmartts sp. classified as stunned supports the validity of the initial qualitative decision based on behavior. Therefore. the alive. stunned and dead viability observations are more sensitive than a two classification system of only alive and dead organisms.
Ahumktnce Gammarus sp. in the Hudson River estuary undergo vertical diel migrations which are reflected as increased intake station abundances during night sampling periods. Mean intake abundances at night were approximately an order of magnitude higher than during the day (Table 3). The distribution of Gammarz~s sp. in the intake and discharge canals also shows a marked vertical stratification, with highest abundances occur-
Table 4. 48 h Survival of Gammarus sp. collected at Indian Point Unit 1 Temperature (°C) Intake 20.0-20.6 Discharge 20.0-20.6 AT 0
Station Intake D-I D-2 D-I
Intake 17.2-20.0 Discharge 2 I. 1-26. I AT 3.9-6.1
During chlorination Intake D- t D-2 D- 1 During chlorination
~
Per cent survival 4.8 h
Alive Alive Alive Stunned
100 100 125 107
97.0 97.0 97.6 24.3
Alive Alive Alive Stunned
i 66 71 79 166
92.2 93.0 9 I. I 26.5
Condition
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Samples collected during periods of conden~r chlorination reveal significant increa~s in abundance at stations D-I and D-2 when compared ~ith prechlorination abundances (Table 31.
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Fig. 5. "i'emr~rature tolerance of G.mmarus sp. at an
ambient temperature of 24.7-25.8 C. ring near the bottom during both day and night sampiing periods (Fig. 6). The analyses of variance of abundance during both day and night sampling periods reveal depth and stations as significant (P < 0.01) factors. No interactions are significant. SNK analyses indicate that the mean intake abundances during both day and night sampling periods are higher than the abundances at stations b - I and D-2. Mean abundances at the two diEharge stations were not significantly different. During the night all three depths for all stations were different from each other in abundance of Gammarus sp. During the day, surface and mid-depth abundances were not distinguishable: however, the abundance was significantly higher in samples from near the bottom.
In past literature, temperature tolerance data have been generally presented in terms of 50 per cent tolerance limits for exposure times of 24 96 h. Since the transit times of electric power plants employing oncethrough cooling are usually less than I h. long-term tolerances are generally not relevant for predictive studies on entrainment effects. Sprague (1963) reported the 24-h LC50's of G. /iv.sciatus acclimated to l0 and 20;C as about 30 and 32 C. respectively. The 24-h LD-50 of G..lasciar,s was determined by Mihursky and Kennedy (1967) to be 31.6C at an ambient of 15-16 C. In this stud) the 4,~-h TL,., of Gammar,s sp. at 25 C ambient was 33.0 C. which is comparable with the 24-h tolerances of G./asc'iatus. However, the TL.~o temperatures derived from tests run at 25-C ambient for exposure times of 5. 30 and 60 rain were 38.7, 37.8 and 36.8 C r~pectively, The difference in temperatures resulting in 50 per cent mortality between the 24- and 48-h tests and the 5. 30 and 60rain tests demonstrates the potential problem of using the longer term TL~o temperatures for predicting mortality resulting from short term exposures. The ultimate goal of bioassays is generally the establishment of non-effect level of the stress being investigated, Coutant (1972) has suggested that an exposure temperature 2:C less than the TL~,, for an equivalent exposure time may be a safe temperature for fish. The
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Fig. 6. Abundance of Gammarus sp. collected during the night (2000-0100 h) at Indian Point Unit I from I I July to 19 September, 1972. Horizontal lines are the means of log-transformed data. Rectangles are the 95 per cent confidence limits of the mean.
944
T.C. Gixx. WILLIAMT. WALLERand GERALDJ. LAISER
2°C safety factor also appears to exist for acute survival of Gammarus sp., since a reduction of 2~C generally places the exposure temperature well below the TL,,~. The TLo.~ values are not necessarily presented as "safe" temperatures. An understanding of the population dynamics of Gammarus sp. in the Hudson estuary would be required before a 5 per cent inital mortality could be determined as acceptable. T L ~ ' s may, however, be used as estimates of tolerance limits above which immediate measurable mortalities would be expected to occur. Consequently, the TL,,~ is a valuable measurement when used in conjunction with entrainment survival studies since it permits the prediction of lethal discharge temperatures. It is generally undesirable to apply thermal tolerance data from one organism to other organisms, even if they are closely related forms. New York University Medical Center (1973) indicates that the other major entrained Hudson River invertebrates, Neomysis americana and Monoculodes edwardsh may be considerably less heat tolera,nt then Gammarus sp. The LD-50 temperatures of seven Patuxent estuary invertebrates were found to vary about 10~C from the most sensitive to the most tolerant (Mihursky and Kennedy, 1967). The relationship of increasing temperature tolerance limits with increasing ambient temperature has been reported previously for several macroinvertebrates species (Hair. 1971 ; Sprague. 1963). This is an importam consideration in thermal effects studies. An organism can generally tolerate considerably higher AT's in winter, although the absolute tolerance limit is lower during the cooler ambient temperatures. Enlrainmenr samplii~j
Although discharge temperatures at Indian Point during the study would not be considered lethal based on laboratory bioassays, some reduction in survival was observed in the discharge canal at station D-1. The observed mortality may be the result of some undetermined factor(s) either individually or in combination with temperature. Nevertheless. it is apparent that most of the entrained Gammaru~ sp. passed through the condenser cooling system without immediate adverse effects on survival. The maximum adverse effects on the survival of entrained Ganunarus sp. are observed during periods of condenser chlorination. Since chlorination at Indian Point occurs for a maximum total period of 3h week-~, the overall projected mortality during all plant operating conditions would be minimal. The reduction in abundance at the discharge stations relative to intake abundance may be due to active or passive movement of organisms to the but-
tom of the discharge canal. If such a redistribution of organisms occurred, it must have been primarily between the discharge water box and station D- 1. since the abundance does not appear to change between stations D-I and D-2. The suggestion that entrained Gammarus sp. are actively moving to the bottom of the discharge canal during normal operating conditions is supported by the increases in discharge canal abundances during chlorination. If settling out of dead organisms were responsible for the reduced discharge canal abundances, then the reductions should be maximum during chlorination when observed mortality is highest. The importance of the proper selection of discharge canal sampling stations in entraintr~nt studies is exemplified by the relative survival at stations D- I and D-2. Collections of Gammarus sp. at D-2 had consistently higher survivals than at D- 1. although organisms at D2 were exposed to thermal stresses for a longer period. If samples were collected only at D-L there would be no evidence for entrainment mortalities except during chlorination. Dead and stunned Gamniarus sp., which are subject to sampling at D-I, most likely settle to the bottom and are not sampled at D-2. Since discharge temperatures were always sublethal during the sampling period, no increases in mortality due to temperature could be expected between D-I and D-Z Acknowledgement--This research was supported by Consolidated Edison Co. Inc, New York. N.Y., U.S.A. REFERENCES
Bousfield E. L. (1969) New records of Gummarus (crustacea: amphipoda) from the middle Atlantic region. Chesapeake Sci. I0, 1-17. Consolidated Edison Company of New York (1973) Enriromnental Report for Ind,,~:z Point Unit No. 3, Vol. I
Coutant C. C. (1972) Biolog:c~'iaspects of thermal pollution II--Scientific basis for v,ater temperature standards at power plants. CRC Reriews m Enrironmental Control, August. 1972. Hair J. R. (1971) Upper lethal temperature and thermal shock tolerances of the opossum shrimp. Neomysis awatschensis, from the Sacramento-San Joaquin estuary. California. Cal~ Fish and Game. 57, 17-27. Heinle D. R, (1969)Temperature and zooplankton. Chesapeake Science 10, 186-.-209. lcanberry J. W. and Adams J. R. ( 19731Zooplankton survi~at in cooling water systems of four thermal power plants on the California coast. Interim Report March 1971-Januar5 1972. Proceedings of the Entrainment and Intake Screeninfj Work.shop, February 5-9. 1973. The Johns Hopkins University. Baltimore, Maryland. In press. Kelly R. (1971} Mortality of Neomysis awatschensis (Brant) resulting from exposure to high temperatures a~ Pacific Gas and Electric Company's Pittsburgh power plant. Calif. Dept. of Fish and Game, .4had. Fish Br. Admin. Rept. 71-3, 6 pp.
P~*~cr plant condenser cooling Markowski S. ( 1960~ Observations on the response of some benthonic organisms to power st:ilion cooling water. J. AnmL Ecol. 29. 349-357. Mihursky J. A. and Kenned)' V. S. (1967) Water temperature criteria to protect aquatic life. In: A Symposium on Water Quality Criteria to Protect .4quatic Life. Special Publ. No. 4 20-32. Amer. Fish Soc.. Washington. D.C. Ne~ York Universit) Medical Center ql9731 Hudson River Ecosystem Studies. Effects of Entrainment b.~ the Indian Point Power Plant on Hudson River Estuary Biota. Progress Report for 1971 and 1972. Prepared for Consolidated Edison ( o . of N.Y. b~ NYU Medical Center. institute of Environmental Med'icine. Laborator) b r Environmental Studies. Nex~ York 309 pp.
~45
Sokal R. R. and Rohlf F. J. (!9691 Biometry. W. H. Freeman. San Francisco. California 776 pp. Sprague J. B. (1963) Resistance of four freshv, ater crustaceans to lethal high temperature and low oxygen. J. Fi4~ ~es. Bd. Canada. 20, 387-415. T~xas Instruments, Inc. (1972) H,~dsos1 Rircr Ecolo#ic,d Study in tl,e Art'a of Indian Point. First Semiannual Report to the Consolidated Edison Company. Vol. I. Biological Sampling. Welch B. L. (1947)The generalization of Student's problem when several different population variances are invoh~d. Bionletrika. 34. 28-35.
THE EFFECTS OF POWER PLANT CONDENSER COOLING WATER ENTRAINMENT O'N THE AMPHIPOD. GAMMARUS sp. T~to,s~s C. Gtxg, WILLIAMT. WALLERand GERALDJ. LAUER New York University Medical Center, Laboratory for Environmental Studies. 550 First Avenue. New York 10016. U.S.A. (Receired 20 May 19741 Abstract--The abundant Hudson River amphipod Gammarus.sp. was examined for viability before and during entrainment in the Indian Point cooling water system. The mean per cent survivial of Gummarus sp. sampled during AT's of 7.1-8.3°C and ambient temperatures of 24.9-26.0 C was 98.5 and 97.4 per cent for the two intake stations and 90.1 and 96.8 per cent for the discharge canal stations D- 1 and D-2 respectively. A statisticaU.,, significant I:t ,= 0.05) difference was detected between the survivial of Gammarus sp. at the intake stations and di~harge station D-I, located near the upper end of the di~harge canal. Entrained Gammarus sp. experience increased initial and latent mortalities during periods of condenser chlorination. Comparison of the abundances of entrained Gammarus sp. during day and night sampling periods reveals a significantly higher occurrence during darkness. Temperature bioassays indicate that the thermal tolerance of Gummarus sp. is dependent on exposure time and ambient temperature. The temperature resulting in a 50 per cent mortality of Gammarus sp. for 30 rain exposure times, increased approximately I 1 C as ambient temperatures increased from 2.5 to 25.8"C. Consequently. GammuJ'ussp. was capable of surviving A'l-s of greater magnitude as the ambient temperature to which they were acclimated decreased. Temperature bioassays indicated that Gammarus sp. should be able to tolerate all projected time-temperature exposure combinations encountered during entrainment through the cooling water system.
INTRODUCTION
The purpose of this study was to determine the effects of condenser cooling water entrainment on the estuarine amphipod. Gammarus sp. This was done by laboratory thermal tolerance tests and by comparing the conditions of Ga~mnarus sp. taken from the plant's cooling water intake and from the discharge canal. This research is part o f a 5-yr program of studies of the Hudson River estuar~ begun in 1969 and supported b) Consolidated Edison Company of New York. Three research organizations are primarily involved in the overall study p r o v a m : New York University Medical Center, Laboratory for Environmental Studies is investigating plant operation effects on nonscreenable organisms: Texas Instruments Incorporated is studying effects on screenable organisms; Q u i r e Lawler and Matusky Engineers is developing a mathematical model for predicting ent~inment effects on striped bass populations. Gamntarus sp. is the most abundant species among the macroinvertebrate zooplankton entrained at Consolidated Edison's Indian Point nuclear power plant on the Hudson River estuary (NYU Medical Center, 1973). This amphipod is the major food orDnism of juvenile ( < 150 mm) striped bass. Morone saxatilis, in w.g. 8'11--F
the Hudson River and is also an important "food organism for adult and juvenile white perch .Xloro,e americana tTexas Instruments. 19721. Gam,~srus sp. appears morphologioally similar to G. tigrinus: however. ~an overlap of characteristics, especially in the juvenile stages, between G. ti.qrmux and G. daiheri makes exact species identification dil?icult (Bousfield. 19691. Due-to the extremel.v large number of organisms collected, no identification beyond Gamngtrtts sp. was attempted. Few studies on the survivial of entrained zooplankton have been reported. Markowski (1959) indicated that several zooplankton species, including gammarid amphipods, were able to survive passage through the condenser cooling system of a steam electric station. However, that report lacked quantitative information on ambient temperature. AT and chlorination. Kelly (1971) observed a 65 per cent mortality of entrained Neomysis awatschensis at discharge temperatures exceeding 90¢F. Mortality was less than 10 per cent at discharge temperatures from 80 to 86:F, which agreed with Kelly's laboratory temperature tolerance experiments. Heinle (19.69) reported up to 100 per cent mortality of entrained eggs and early nauplii of Acartia tonsa, although discharge temperatures were below the 937
938
T.C. GINN. WILLIA~,IT. WALLERand GERALDJ. LAL:ER
laboratory-predicted tolerance limits. A subsequent analysis (Heinle, personal communication)indicates that the high mortalities were associated with periods of condenser chlorination, lcanberry and Adams (1973) reported a mean mortality difference between intake and discharge zooplankton samples of 5.97 per cent. Discharge temperatures ringed from 48.6 to 85.0':F. There was no apparent difference in 24h delayed mortalities between intake and disc,barge samples maintained in ambient water baths.
MATERIALS'AND METHODS All tests were conducted at the Indian Point plant, which ison the Hudson River estuary at mile 43 above
the Battery. When operating at its rated capacity of 265 MWe, the plant's Unit I has a cooling water demand of approximately 280,000gal rain-t. The design AT is 7.2~C. Water enters the condenser cooling system through four shorelide intakes and is discharged in a 300 m long canal that will also be used by Units 2 and 3. The discharge canal terminates in a sub-surface diffuser system(see Fig. l). When Unit l is operating alone, the time of water travel from the Unit I condenser to diffuser outfalls ranges from 32 to 53 min, depending on flow. The transit time of water from the condensers to the discharge ports will be reduced to as little as 6-9.5 rain by increased flows during multiunit operation. (Con~iidated Edison Company at New York. 1973). After exit from the diffuser ports the AT of the discharge, when only Unit I is operating, is reduced by dilution to 50 per cent in less than 2 s and 95 per cent in 20 s. The dilution rate would be considerably slower during multi-unit operation.
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Laboratory thermal tolerance test Gammur,ts sp. for laboratory temperature-tolerance tests were collected using 500 ~m mesh plankton nets which were 0.5 m din and 2 m long. A 90 x 230 mm PVC bucket with a lateral 500 lu'n screened opening (63 x I(X)ram) was attached to the codend of the net. Test organisms were collected from the plant intakes and maintained in ambient temperature baths for 48 h before thermal tolerance experiments. Each test group consisted of 25 organisms which were selected to approximate the size composition of the river population of Gammarus sp. at the time samples were taken. Test organisms were sorted into [25-ml methylpentene polymer containers with bottoms of 500/tm mesh nylon netting. To obtain thermal exposures of desired temperatures and durations test containers with Gammarus sp. were immersed in constant-temperature water baths filled with aerated Hudson River water. Temperature was monitored continuously with a thermister telethermometer. At the end of the selected exposure time the test containers were immediately transferred to an ambient temperature bath. The instantaneous drop to ambient temperature, following exposure to elevated temperature, was designed to approximately simulate the thermal regime at the Indian Point submerged discharge ports. Control groups of Gammaru.s sp. were placed in the test containers and maintained at ambient temperature. Test organisms were examined for viability l h after thermal exposure. During summer ambient temperatures, test organisms were held at ambient temperature in the laboratory for examination 24 h after thermal tolerance tests. Organisms lacking pteopodal movement were classified as dead. Other behavioral characteristics, such as
I
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Fig. I. Schematic of the Indian Point cooling water system.
I'owcr plant condenser cooling locomotor abilit.~, stimulus respond, and spatial orientation were also noted throughout the tests.
Intake and discharge canal ,~mpling Samples of Gammarus sp. were collected on two dates each week (one day. one night) from 27 June to 24 August, at which time the day sampling was discontinued and onl) night samples were collected until 26 September. Collections were made at two of the Unit I intake bays(l-I and ]-2). in the discharge canal near its exits from the plant (D-I)and just prior to the first submerged diffu~r port (D-2)(Fig. It. Samples were taken at the surface, mid-depth, and bottom at each station, with nets of the type already discussed. Surface samples were collected by lowering a heavilyweighted net from a platform located over each station. M id-depth and bottom samples were collected by nets mounted on rigid PVC frames which were lowered to the desired depth on a vertical track. A total of 428 samples containing 59.602 Gammarus sp. were collected during the stud) period. Only samples containing more than five organisms (307 samples) were used for viability analysis. Since an air-curtain bubbler system was normally in operation at l-I. only I-2 samples were used for intake abundance estimates. Sampling time was normally 5rain: however, increased zooplankton densities occasionally required a reduction of sampling time to I rain. Collections were immediatel) transported to the laboratory at the plant and maintained in an ambient water table during examination. Collected organisms were classified as alive, stunned or dead by the same person throughout the study period. Stunned Gammarus sp. displayed little response to probing stimuli and reduced locomotor activity. Any dead or stunned organisms were immediately enumerated and removed from the sample. The collection was then preserved in 10",, formalin and the remainder of the organisms were counted later. Samples were collected before and during chlorination on each date. Sodium hypochlorite was injected into the cooling water prior to the intake pumps at a pre-arranged time. Normal chlorination procedure called for the addition of chlorine for 30 min to only one of the two circulating pumps at a time. Consequently, only 50 per cent of the cooling water flow received a chlorine injection prior to the confluence of the condenser water boxes at "the discharge canal. Beyond this point water from the chlorinated pump mixes with the flow from the untreated pump, resulting in a 1: I dilution of the chlorinated water in the discharge canal. Mean total chlorine residuals measured by the amperometric method at the water box and in the discharge canal were approximately 0.29 mg 1-J and 0.11 mg l-~, respectively. Groups of alive and
93,~
stunned Ganmvarus sp. were selected from intake and discharge samples and examined for viability 4,~ h after collection. The organisms were maintained in aerated HkJdson River water at ambient temperature. Amdysis of t'ariance Statistical analyses of Gammarus sp. abundance followed the method of Sokal and Rohlf(1909) for factorial analysis of variance with balanced design. Eleven night sampling dates and 6 day sampling dates were .~[ected for three way analyses of variance, i.e. for depth (surface. mid-depth and bottomL station (intake. D-I and D-2L and date. The abundances were transformed by Iog,ox + I to make the data conform to the assumption of homogeneity of variances. Differences between means of an). significant factor in the overall analysis were examined b) the Student-Newman Keuls procedure.
R ESU LTS
Temperature tolerance Gammarus sp. display pronounced seasonal variations in acute thermal tolerance, corresponding with changes in ambient river temperature. Temperaturesurvival curves for 30-rain exposures over an ambient temperature range of 2.5--25.8~C arc presented in Fig. 2. Figures 3 and 4 represent the relationship between 50 and 95 per cent tolerance limits (derived from logprobit analysis) and ambient temperature. These tolerances are the temperatures which result in projected survival of 50 and 95 per cent of exposed organisms. These data indicate that Gummarus sp. can tolerate about an I I C higher temperature during summer ambient temperatures than in winter. Once lethal
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Fig. 4. 95"° Temperature tolerance limits for Gammarus sp,
exposure temperatures are reached, the mortality response of Gammarus sp. is pronounced, since the TL~,, values are generally less than 2:C higher than the TL~.~'s. Exposure time was found to be an important factor in the response of Gammarus sp. to thermal shock. During most of the year. the test organisms could tolerate approximately 1.5-2.0°C higher temperatures for 5 rain than for 60rain (Fig. 3. 4 a n d 5). The test organisms also tolerated considerably higher temperatures during short-term exposures (5-60 rain) when compared with a '48-h exposure time (Fig. 4). The 60rain tolerance Iimits were approximately 5°C higher than the 48-h tolerance limits at an ambient temperature near 25"C. At an ambient of 25"C Gammarus sp. exposed for 5-60 rain to test temperatffres up to 35:C sur,,ived the full observation time of 24 h. However. 24-h survisal rapidly decreases as test temperature increase above 37°C (Table I). During sub-lethal temperature exposures, the test organisms were generally hyperactive. As test temperatures approach to within about 2~'C of the 60min
TL,,,. a pronounced shock reaction was noted as the test groups were returned to ambient temperature. Although hyperactive in the temperature bath. the organisms immediately lost orientation and mobility for periods of up to 0.5 h after return to ambient temperature. When exposed to lethal temperatures, test organisms generally displayed an almost instantaneous loss of mobility. Some isolated darting occurred during the exposure, but most test organisms were disoriented and unresponsive. This reaction was observed throughout the ambient temperature range at exposure temperatures exceeding the 60-rain TL,,,. The temperature which produces this stunned effect is usually referred to as the critical thermal maximum.
Intake-discltarqe riability The condition of GammamJs sp. collected in 307 samples at Indian Point Unit I is presented in Table 2. The mean per cent alive exceeded 90 per cent at all stations except during periods of condenser chlorination. The mean percentage alive and their 95 per cent confidence intervals at each station during all plant operational
Table 1. Latent mortality of thermally shocked Gammarus sp. at ambient temperatures of 24.7-25.8 C
Test temperature (°C) 33.0 34.2 35.6 37.0 37.5 37.8 38.3 38.9
5 0 0 2 0 0 0 14 100
Per cent mortality of organisms surviving initial thermal shock Exposure time Imin) ~5 30 60 0 0 0 .I 9 0 40 .
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0 0 0 92 90 --.
Control 0 0 0 0 0 0 0 0
Organisms surviving initial 5-60 minute thermal shocks were returned to ambient temperature and examined for mortality 24 h later.
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T. C. Gl.xx. WILLIAX!T. WALLERand GERAL,DJ. LALI.~
942
Table 3. Abundance of Gammarus sp. collected at Indian Point Unit I Iogto of N o I000 m - 3 Day Night ( 13 July- 17 August~ t I I July- 19 Septcrnber~
Station
Intake
2.641 ( Z 0.4631" 2.042 (+0.318) I. 167 ( _ 0.6301 3.223 ~__.0.521 ) 2.784 ( ± 0.629)
D- I D-2 D-I during chlorination D-2 during chlorination
3.858 I ± 0.253t 3.375 (_+0.2711 34"/5 I ± 0.283) 4.2(11 i ~ 0.2571 4.31 I _ 0.256)
* 950; Confidence limits of the mean conditions were: Intake. 96.9 + 0.76; D-I. 9..2.1 +_ 2.37: D-Z 95.3 + 1.87; D-I chlorination. 54.6 + 7.96: and D-2 chlorination. 74.9 + 8.49. Analysis of variance was not conducted on the survival of entrained Gammarus sp. since no adequate normalizing and/or variance stabilizing tran,h>rmation was found. However, a r*-test which assumes unequal variances (Welch, 1947) indicates a significant reduction in survival at station D-I when compared with the intakes during theperiod of maximum AT's (7.1-8.3"C). The survival at station D-2 was not different from ,ntake survival. Significant reduct;ons in survival were indicated during periods of condenser chlorination at both discharge stations. The per cent alive was lowest at station D-I during the full AT range of 4.4--8.3 C. Approximately 50 per cent of the Gammarus sp. in the samples were alive, the remaining 50 per cent were almost equally divided among dead and stunned categories. Groups of alive Gammarus sp. captured in the discharge canal during plant operation displayed no
latent mortality when compared with intake control samples during the 48 h observation period after collection (Table 4). However. approximately 75 per cent of the stunned organisms collected in the discharge canal during chlorination died within 48 h. The pronounced latent mortality of those Gdmmartts sp. classified as stunned supports the validity of the initial qualitative decision based on behavior. Therefore. the alive. stunned and dead viability observations are more sensitive than a two classification system of only alive and dead organisms.
Ahumktnce Gammarus sp. in the Hudson River estuary undergo vertical diel migrations which are reflected as increased intake station abundances during night sampling periods. Mean intake abundances at night were approximately an order of magnitude higher than during the day (Table 3). The distribution of Gammarz~s sp. in the intake and discharge canals also shows a marked vertical stratification, with highest abundances occur-
Table 4. 48 h Survival of Gammarus sp. collected at Indian Point Unit 1 Temperature (°C) Intake 20.0-20.6 Discharge 20.0-20.6 AT 0
Station Intake D-I D-2 D-I
Intake 17.2-20.0 Discharge 2 I. 1-26. I AT 3.9-6.1
During chlorination Intake D- t D-2 D- 1 During chlorination
~
Per cent survival 4.8 h
Alive Alive Alive Stunned
100 100 125 107
97.0 97.0 97.6 24.3
Alive Alive Alive Stunned
i 66 71 79 166
92.2 93.0 9 I. I 26.5
Condition
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Samples collected during periods of conden~r chlorination reveal significant increa~s in abundance at stations D-I and D-2 when compared ~ith prechlorination abundances (Table 31.
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Fig. 5. "i'emr~rature tolerance of G.mmarus sp. at an
ambient temperature of 24.7-25.8 C. ring near the bottom during both day and night sampiing periods (Fig. 6). The analyses of variance of abundance during both day and night sampling periods reveal depth and stations as significant (P < 0.01) factors. No interactions are significant. SNK analyses indicate that the mean intake abundances during both day and night sampling periods are higher than the abundances at stations b - I and D-2. Mean abundances at the two diEharge stations were not significantly different. During the night all three depths for all stations were different from each other in abundance of Gammarus sp. During the day, surface and mid-depth abundances were not distinguishable: however, the abundance was significantly higher in samples from near the bottom.
In past literature, temperature tolerance data have been generally presented in terms of 50 per cent tolerance limits for exposure times of 24 96 h. Since the transit times of electric power plants employing oncethrough cooling are usually less than I h. long-term tolerances are generally not relevant for predictive studies on entrainment effects. Sprague (1963) reported the 24-h LC50's of G. /iv.sciatus acclimated to l0 and 20;C as about 30 and 32 C. respectively. The 24-h LD-50 of G..lasciar,s was determined by Mihursky and Kennedy (1967) to be 31.6C at an ambient of 15-16 C. In this stud) the 4,~-h TL,., of Gammar,s sp. at 25 C ambient was 33.0 C. which is comparable with the 24-h tolerances of G./asc'iatus. However, the TL.~o temperatures derived from tests run at 25-C ambient for exposure times of 5. 30 and 60 rain were 38.7, 37.8 and 36.8 C r~pectively, The difference in temperatures resulting in 50 per cent mortality between the 24- and 48-h tests and the 5. 30 and 60rain tests demonstrates the potential problem of using the longer term TL~o temperatures for predicting mortality resulting from short term exposures. The ultimate goal of bioassays is generally the establishment of non-effect level of the stress being investigated, Coutant (1972) has suggested that an exposure temperature 2:C less than the TL~,, for an equivalent exposure time may be a safe temperature for fish. The
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944
T.C. Gixx. WILLIAMT. WALLERand GERALDJ. LAISER
2°C safety factor also appears to exist for acute survival of Gammarus sp., since a reduction of 2~C generally places the exposure temperature well below the TL,,~. The TLo.~ values are not necessarily presented as "safe" temperatures. An understanding of the population dynamics of Gammarus sp. in the Hudson estuary would be required before a 5 per cent inital mortality could be determined as acceptable. T L ~ ' s may, however, be used as estimates of tolerance limits above which immediate measurable mortalities would be expected to occur. Consequently, the TL,,~ is a valuable measurement when used in conjunction with entrainment survival studies since it permits the prediction of lethal discharge temperatures. It is generally undesirable to apply thermal tolerance data from one organism to other organisms, even if they are closely related forms. New York University Medical Center (1973) indicates that the other major entrained Hudson River invertebrates, Neomysis americana and Monoculodes edwardsh may be considerably less heat tolera,nt then Gammarus sp. The LD-50 temperatures of seven Patuxent estuary invertebrates were found to vary about 10~C from the most sensitive to the most tolerant (Mihursky and Kennedy, 1967). The relationship of increasing temperature tolerance limits with increasing ambient temperature has been reported previously for several macroinvertebrates species (Hair. 1971 ; Sprague. 1963). This is an importam consideration in thermal effects studies. An organism can generally tolerate considerably higher AT's in winter, although the absolute tolerance limit is lower during the cooler ambient temperatures. Enlrainmenr samplii~j
Although discharge temperatures at Indian Point during the study would not be considered lethal based on laboratory bioassays, some reduction in survival was observed in the discharge canal at station D-1. The observed mortality may be the result of some undetermined factor(s) either individually or in combination with temperature. Nevertheless. it is apparent that most of the entrained Gammaru~ sp. passed through the condenser cooling system without immediate adverse effects on survival. The maximum adverse effects on the survival of entrained Ganunarus sp. are observed during periods of condenser chlorination. Since chlorination at Indian Point occurs for a maximum total period of 3h week-~, the overall projected mortality during all plant operating conditions would be minimal. The reduction in abundance at the discharge stations relative to intake abundance may be due to active or passive movement of organisms to the but-
tom of the discharge canal. If such a redistribution of organisms occurred, it must have been primarily between the discharge water box and station D- 1. since the abundance does not appear to change between stations D-I and D-2. The suggestion that entrained Gammarus sp. are actively moving to the bottom of the discharge canal during normal operating conditions is supported by the increases in discharge canal abundances during chlorination. If settling out of dead organisms were responsible for the reduced discharge canal abundances, then the reductions should be maximum during chlorination when observed mortality is highest. The importance of the proper selection of discharge canal sampling stations in entraintr~nt studies is exemplified by the relative survival at stations D- I and D-2. Collections of Gammarus sp. at D-2 had consistently higher survivals than at D- 1. although organisms at D2 were exposed to thermal stresses for a longer period. If samples were collected only at D-L there would be no evidence for entrainment mortalities except during chlorination. Dead and stunned Gamniarus sp., which are subject to sampling at D-I, most likely settle to the bottom and are not sampled at D-2. Since discharge temperatures were always sublethal during the sampling period, no increases in mortality due to temperature could be expected between D-I and D-Z Acknowledgement--This research was supported by Consolidated Edison Co. Inc, New York. N.Y., U.S.A. REFERENCES
Bousfield E. L. (1969) New records of Gummarus (crustacea: amphipoda) from the middle Atlantic region. Chesapeake Sci. I0, 1-17. Consolidated Edison Company of New York (1973) Enriromnental Report for Ind,,~:z Point Unit No. 3, Vol. I
Coutant C. C. (1972) Biolog:c~'iaspects of thermal pollution II--Scientific basis for v,ater temperature standards at power plants. CRC Reriews m Enrironmental Control, August. 1972. Hair J. R. (1971) Upper lethal temperature and thermal shock tolerances of the opossum shrimp. Neomysis awatschensis, from the Sacramento-San Joaquin estuary. California. Cal~ Fish and Game. 57, 17-27. Heinle D. R, (1969)Temperature and zooplankton. Chesapeake Science 10, 186-.-209. lcanberry J. W. and Adams J. R. ( 19731Zooplankton survi~at in cooling water systems of four thermal power plants on the California coast. Interim Report March 1971-Januar5 1972. Proceedings of the Entrainment and Intake Screeninfj Work.shop, February 5-9. 1973. The Johns Hopkins University. Baltimore, Maryland. In press. Kelly R. (1971} Mortality of Neomysis awatschensis (Brant) resulting from exposure to high temperatures a~ Pacific Gas and Electric Company's Pittsburgh power plant. Calif. Dept. of Fish and Game, .4had. Fish Br. Admin. Rept. 71-3, 6 pp.
P~*~cr plant condenser cooling Markowski S. ( 1960~ Observations on the response of some benthonic organisms to power st:ilion cooling water. J. AnmL Ecol. 29. 349-357. Mihursky J. A. and Kenned)' V. S. (1967) Water temperature criteria to protect aquatic life. In: A Symposium on Water Quality Criteria to Protect .4quatic Life. Special Publ. No. 4 20-32. Amer. Fish Soc.. Washington. D.C. Ne~ York Universit) Medical Center ql9731 Hudson River Ecosystem Studies. Effects of Entrainment b.~ the Indian Point Power Plant on Hudson River Estuary Biota. Progress Report for 1971 and 1972. Prepared for Consolidated Edison ( o . of N.Y. b~ NYU Medical Center. institute of Environmental Med'icine. Laborator) b r Environmental Studies. Nex~ York 309 pp.
~45
Sokal R. R. and Rohlf F. J. (!9691 Biometry. W. H. Freeman. San Francisco. California 776 pp. Sprague J. B. (1963) Resistance of four freshv, ater crustaceans to lethal high temperature and low oxygen. J. Fi4~ ~es. Bd. Canada. 20, 387-415. T~xas Instruments, Inc. (1972) H,~dsos1 Rircr Ecolo#ic,d Study in tl,e Art'a of Indian Point. First Semiannual Report to the Consolidated Edison Company. Vol. I. Biological Sampling. Welch B. L. (1947)The generalization of Student's problem when several different population variances are invoh~d. Bionletrika. 34. 28-35.