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Home , Biomass (ecology), Ecology, Lake ecosystem, Limnology, Productivity (ecology), Trophic state index

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A for lakes1 THIS WATERIALI.tA r Be PROTecTED BYCOPYRIGHTI.A~ Robert E. Carlson . (T;T~:- "1?t 1.8.£) Limno IOglCal Research2 Center, , Minneapolis 55455

Abstract A numerical trophic state index for has been developed that incorporates most lakes in a scale of 0 to 100. Each major division (10, 20, 30, etc.) represents a doubling in algal . The index number can be calculated from any of several parameters, including Secchi disk transparency, , and total .

My purpose here is to present a new ap- sometimes circumvented by classifying proach to the trophic classificationof lakes. lakes that show characteristics of both oli- This new approach was developed because gotrophy and eutrophy as mesotrophic. of frustration in communicatingto the pub- Two or three ill-defined trophic states lic both the current or status of lakes cannot meet contemporary demands for a and their future condition after restoration sensitive, unambiguous classification sys- when the traditional trophic classification tem. The addition of other trophic states, system is used. The system presented here, such as ultra-oligotrophic, meso-eutrophic, termed a trophic state index (TSI), in- etc., could increase the discrimination of the volves new methods both of defining index, but at present these additional divi- trophic status and of determining that status sions are no better defined than the first in lakes. three and may actually add to the confu- All trophic classification is based on the sion by giving a false sense of accuracy and division of the trophic continuum, however sensitivity. this is defined, into a series of classes I acknowledgethe advice and encourage- termed trophic states. Traditional systems ment of J. Shapiro in developing this index divide the continuum into three classes: and in preparing the manuscript. I also oligotrophic, mesotrophic, and eutrophic. thank C. Hedman and R. Armstrong for ad- There is often no clear delineation of these vice and H. Wright for help in manuscript .. divisions. Determinations of trophic state preparation. are made from examination of several di- verse criteria, such as shape of the Cu"ent approaches curve, composition of the bottom The large number of criteria that have or of the , concentra- been used to determine trophic status has tions of , and various measures of contributed to the contention that the biomass or production. Although each trophic concept is multidimensional, in- changes from oligotrophy to eutrophy, the volvingaspects of loading, nutrient changes do not occur at sharply defined concentration, , faunal and places, nor do they all occur at the same floral quantity and quality, and even place or at the same rate. Somelakes may morphometry. As such, trophic status be considered oligotrophic by one criterion could not be evaluated by examining one or and eutrophic by another; this problem is two parameters. Such reasoning may have fostered multiparameter indices (e.g. Bre- 1Contribution 141 from the Limnological Re- search Center, University of Minnesota. This work zonik and Shannon 1971; Michalski and was supported in part by Environmental Protec- Conroy 1972). A multiparameter index is t I tion Agency training grant U910028. limited in its usefulnessbecause of the num- I · Present address: Department of Biological Sciences, Kent State University, Kent, Ohio ber of parameters that must be measured. 44242. In addition, the linear relationship assumed UMNOLOGY AND 361 MARCH 1977, v. 22(2) 362 Carlson

between the parameters in some of these I chose algal biomass as the key descrip_ indices does not hold as evidence presented tor for such an index largely because algal below indicates. bloomsare of concern to the public. An in- Alternatives to the multidimensional dex that is particularly sensitive to such trophic concept have been based on a sin- concern would facilitate communicationbe- gle criterion, such as the rate of supply of tween the limnologistand the public. either organic (Rodhe 1969) or nu- Values for algal biomass itself are diffi- trients (Beeton and Edmondson 1972) into cult to use in the index because biomassis a lake. Indices based on a single criterion a poorly defined term, usually in turn esti- potentially could be both unambiguous and mated by one or more parameters such as sensitive to change. However, there is cur- dry or wet weight, volume, particulate rently no consensus as to what should be , chlorophyll, or Secchi disk trans- the single criterion of trophic status, and parency. I constructed the index using the it is doubtful that an index based on a sin- range of possible values for Secchi disk gle parameter would be widely accepted. transparency. In addition to having values easily transformed into a convenient scale, Basisfor a new index Secchi disk transparency is one of the sim- The ideal trophic state index (TSI) plest and most often made limnological should incorporate the best of both the measurements. Its values are easily under- above approaches, retaining the expression stood and appreciated. of the diverse aspects of trophic state found The relationship between algal biomass in multiparanleter indices yet still having and Secchi disk transparency is expressed the simplicity of a single parameter index. by the equation for vertical of This can be done if the commonly used light in trophic criteria are interrelated. The evi- dence is that such is the case. Vollenweider I"= Ioe-(k-+kt>.8, (1) (1969, 1976), Kirchner and Dillon (1975), whereIe= light intensityat the depth at and Larsen and Mercier (unpublished) which the Secchi disk disappears, 10=in- have developed empirical equations to pre- tensityof light strikingthe water surface, dict phosphorus concentration in lakes kw= coefficientfor attenuationof lightby from knowledge of phosphorus loading. water and dissolved substances, kb =coef- Sakamoto (1966) and Dillon and Rigler ficient for attenuation of light by particu- 1 (1974) have shown a relationship between late matter, and z depth at which the vernal phosphorus concentration and algal = .1 biomass,measured as chlorophylla concen- Secchi disk disappears. The term k'b can tration. Lasenby (1975) used Secchi disk be rewritten as aC, where a has the dimen- transparency to predict areal hypolimnetic sions of m2 mg-1 and C is the concentration oxygen deficits. If many of the commonly of particulate matter (mg m-B). Equation i used trophic criteria could be related by a 1 can then be rewritten as series of predictive equations, it would no longer be necessaryto measure all possible trophic parameters to determine trophic status. A single trophic criterion, e.g. algal and rearranged to form the linear equation biomass,nutrient concentration,or nutrient loading, could be the basis for an index from which other trophic criteria could be (~)(ln ~:) = kw+ aC. (3) estimated or predicted by means of the es- III is about 10% of 10 (Hutchinson 1957; tablished relationships. Alternatively, mea- Tyler 1968) and can be considered to be a surements of any of the trophic criteria constant. Alpha may vary depending on could be used to determine trophic status. the size and on the light-absorption and Co

Trophic state index 363

100

o o . . 100 120 o , , , , " . . ", . ;> o 0 100 E o

f 10 o " o '5. . oo , PI 80 o , is . E . , - .'0' CI I . E .~"''''.. ., - , , , , nil 60 0 , , = .. , , s:>. .. a. 0.. . 0L. f". 0' 0 o 0 s: 40 'f · u ... o .. . 20-1 . Ie.. 0.1 1 10 100 . . Secchi Disk Transparency em) .<: ... 0. . "'...... -.. ... _8. 2 G 7 8 9 10 11 12 13

Secch i Disk Transparency (meters) Fig. 1. Relationship between Secchi disk transparency and near-surface concentrations of chloro- phyll a. Insert: log-log transformation of same data. Dashed line indicates slope of 1.0. light-scattering properties of the , ency is inverselyproportional to the sum of but intuitively one would expect the value, the absorbance of light by water and dis- which is the reciprocal of the amount of solved substances (k",) and the concentra- particulate matter per square meter in the tion of particulate matter (C). In many above the Secchi disk, not lakes studied, k",is apparently small in re- to vary as a of algal concentration, lation to C, and hyperbolic curves are ob- and for this discussion it is considered a tained when Secchi disk transparency is constant plotted against parameters related to algal According to Eq. 3, Secchi disk transpar- biomass, such as chlorophyll a (Fig. 1). 364 Carlson

Constructionof the index At the same it retains the original I defined trophic states for the index meaning of the nomenclatural trophic sys- using each doubling of algal biomass as the tem by using major divisions (10, 20, 30, criterion for the division between each etc.) that roughly correspond to existing state, i.e. each time the concentration of concepts of trophic groupings. algal biomass doubles from some base Adc1ltion of other parameters value, a new trophic state will be recog- nized. Because of the reciprocal relation- The regression of Secchi disk against ship between biomass concentration and chlorophylla and total phosphorus was cal- Secchi disk transparency, each doubling in culated from data readily available. The biomass would result in halving transpar- number of data points and the number of ency. By transforming Secchi disk values parameters used can be expanded. The to the logarithm to the base 2, each bio- data used came from Shapiro and Pfann- mass doubling would be represented by a kuch (unpublished), Schelskeet al. (1972), whole integer at Secchi disk values of 1 Powers et al. (1972), Lawson (1972), Me- m, 2 m, 4 m, 8 m, etc. gard (unpublished), and Carlson (1975). I felt that the zero point on the scale Chlorophyll a (Fig. 1) does not give a should be located at a Secchi disk (SD) linear fit to the model predicted in Eq. 2. value greater than any yet reported. The A nonlinear element in the relationship ne- greatest value reported by Hutchinson cessitated a log-log transformlition of the (1957) is 41.6 m in Lake Masyuko,Japan. data. The resulting equation is The next greatest integer on the lo~ scale In SD =2.04- 0.68InChI (5) is at 64 m. A trophic state index (TSI) 0.93, 147), value of 0 at 64 m is obtained by subtract- (r = n= ing the lo~ of 64 from an indexingnumber where SD transparency is in meters and of 6, giving a final TSI equation of Chl a concentration is in milligrams per l cubic meter taken near the sudace. One TSI=10(6-10~SD). (4) possible explanation for this exponential The value is multiplied by 10 to give the relationship may be that as algal density scale a range of 0 to 100 rather than 0 to increases, the become increasingly 10. Two significant digits are all that can light limited. In response to lower light be reasonably expected. The completed per unit cell, more chlorophyll may be pro- scale begins at 0 at SD =64 m, with 32 m duced (Steele 1962). being 10; 16 m, 20j 8 m, 30; etc. The theo- When all available data were included, retical limit is indefinite, but the practical the regression of total phosphorus (TP in limit is 100 or 110 (transparency values of mg m-3) against the reciprocal of Secchi 6.4 and 3.2 em). disk transparency yielded The scale is intentionally designed to be numerical rather than nomenclatural. Be- SD =64.9jTP (6) (r 0.89, n 61). cause of the small number of categories = = usually allotted in nomenclatural systems, Total phosphorus should correlate best there is both a loss of information when with transparency when phosphorus is the lakes are lumped together and a lack of major factor limiting growth. Correlations sensitivityto trophic changes.This problem may be poor during and fall over- is alleviated as more and more trophic turn when algal production tends to be state names are added, but the system soon limited by or light. Prelimi- "', becomes so encumbered that it loses its nary use of the above regression coefficients . appeal. The scale presented here, a nu- in the index suggested that the equation merical classification with more than 100 does predict the average seasonal relation- trophic categories, avoids these problems. ship between total phosphorus and trans- r

Trophic state index 365

Table 1. CompJetedtrophic state index and rophyll, or total phosphorus. The computa- its associatedparameters. tional forms of the equations are Surface "S'ilri'ace Secch1 phosphorus chlorophyll ID- dl~ ~ (mg/m3) TSI(SD) =10(6_1~S~). (11) o 64 0.75 0.04 10 32 1.5 0.12 20 16 3 0.34 30 8 6 0.94 40 4 12 2.6 TSI(ChI) =10(6- 2.04-0~~In Chi), (12) 50 2 24 6.4 60 1 lie 20 and 70 0.5 96 56 80 0.25 192 154 In 48 90 0.12 384 427 100 0.062 ill ~ TSI(TP) =10(6- InT:.) (13) The completedscaleand its associatedpa- parency, but its predictions for phosphorus rametersare shownin 1. are too high in spring and fall and too low during . Because the equation Using the index is to be used in an index where agreement of correlated parameters is emphasized, I Seasonal TSI values for several Minne- decided to use only summer values in the sota lakes are plotted in Fig. 2. The TSI regressionto provide the best agreement of values for total phosphorus tended to fluc- total phosphorus with algal parameters dur- tuate less than those for the biological pa- ing the when sampling would nor- rameters, which approached the values mally be done. based on phosphorus during July and espe- There were not enough data available cially August and September. The extreme for phosphorus and transparency during fluctuations in the TSI based on biological July and August to produce a meaningful parameters in May and June may result regression. Instead, chlorophyll was re- from springtime crashes in algal popula- tions. In Lake Harriet, the chlorophyll and gressed against total phosphorus and the Secchi disk TSI values remained below the resulting equation combined with Eq. 4 to " produce a phosphorus-transparency equa- phosphorus TSI throughout summer. This tion. The chlorophyll-total phosphorus for divergence of the biological TSI values July and August data points yielded from the phosphorus TSI cannot yet be ex- plained, but it does emphasize one of the In Chi = 1.449 In TP - 2.442 (7) strongest advantages of individually deter- (r = 0.846, n = 43 ). mined trophic indices. Allparameters when transformed to the trophic scale should This equation is similar to that derived by have the same value. Any divergence from Dillon and Rigler (1974) for the relation- this value by one or more parameters de- ship between vernal total phosphorus and mands investigation. For example, is it summer chlorophyll: really true that Lake Harriet is P limited, In ChI = 1.449 In TP - 2.616. (8) since it seems to be producing less binmass than the phosphorus levels would suggest? Combining5 with 7 produced Thus, the TSI scale not only classifies the In SD = 3.876 - 0.98 In TP, (9) lake but can serve as an internal check on assumptions about the relationships among or approximately varinus components of the lake . SD 48(ljTP). (10) To use the index for classifyinglakes re- = quires that a single number be generated This equation was used in the index. that adequately reflects the trophic status The trophic state index can now be com- of the lake. It should be emphasized that puted from Secchi disk transparency, chlo- the number generated is only an index of

I . 366 Carlson

80 algal growth and that the concentrations of all forms of phosphorus present are a 60 function of algal biomass. The former as- 40 sumption does not seem to hold during " :zo spring, fall. or (Fig. 2) nor is the [oj ill 70 latter the case in lakes having high ortho- .. phosphorus values (such as some lakes re- 50 HALSTED B4Y ceiving domestic sewage) or in highly col- u lAK£ NlNttE'0.. i 30 ored lakeswhere some forms of phosphorus may be tied up with humic acids (Moyer 10 and Thomas 1970). The advantage of the &0 phosphorus index is that it is relatively 40 stable throughout the year and, because of LAKE tWlRIET 20. this, can supply a meaningful value during .. I .. I .. I A I S I 0 I N seasonswhen algal biomassis far below its Fig. 2. Seasonal variation in tropbic state in- potential maximum. dices calculated from Seccbi disk transparency In instances where the biological TSI ( .), cb1orophyll /J (0), and total phospboros values diverge from that predicted by the ( X) for three Minnesota lakes in 1972. phosphorus index, it is not satisfactory to averagethe different values,as the resulting value would neither represent the trophic the trophic status of a lake and does not state predicted by the nutrient concentra- define the trophic status. In other words, tion nor the biological condition estimated chlorophyllor total phosphorus are not con- from biological criteria. I suggest that for sidered as the basis of a definitionof trophic purposes of classificationpriority be given state but only as indicators of a more to the biological parameters, especially the broadly defined concept. The best indi- chlorophyllindex, during summer, and per- cator of trophic status may vary from lake haps to the phosphorus values in spring, to lake and also seasonally,so the best in- fall, and winter, when the algae may be dex to use should be chosen on pragmatic limited by factors other than phosphorus. grounds. These priorities would result in about the Secchi disk transparency might be ex- same index value during any season of the pected to give erroneous values in lakes year. containing high amounts of nonalgal par- Some period should be identified during ticulate matter, in highly colored lakes which samples should be taken for lake (those with a high kv,), and in extremely classification. It might be argued that sam- clear lakes where kv,again is an important ples should be taken throughout a calen- factor in light extinction. The advantage dar year to include all variations in trophic of using the Secchi disk is that it is an ex- status, but this would require the switching tremely simpleand cheap measurementand of index parameters during the year, as usually provides a TSI value similar to that mentioned above, and the large number of obtained for chlorophylI. samples required might limit the usefulness Chlorophyll a values are apparently free of the index. from interference, especially if the values Basing the index on samples taken dur- are corrected for pheophytin. It may be that the number derived from chlorophyll ing spring or fall turnover would provide is best for estimating algal biomassin most a phosphorus index based on mean phos- lakes and that priority should be given for phorus concentration, a measurement used its use as a trophic state indicator. in most predictive loading models. How- Accurate index values from total phos- ever, some disadvantages of limiting sam- phorus depend on the assumptions that pling to overturn periods are the brief or phosphorus is the major for even nonexistent overturn in some lakes Trophic state index 367

and the possibility of a lessened agreement o with the biologicalparameters. In addition, 70 mean phosphorus concentrations could be calculated at any time if appropriate mor- . -E phometric data were available. An alter- native might be to take epilimnetic sam- ples during summer stratification, when there should be the best agreement between all of the index parameters. This would allow confidence in comparisons between studies that used different parameters. This period would also coincide, in temperate lakes,with peak recreational usage, increas- ing the utility of the index in communicat- ing the meaning of the classificationto the general public. A calculation of TSI values from the 6. yearly data for Lake Washington (Fig. 3), supplied by W. T. Edmondson, also illus- trates the utility of the scale. In 1957,the 60r E.,,_.. lake was receiving 51% of its phosphorus . , from sewage , and there was a no- ;; ticeable deterioration in . ...1 Sewage diversion began in 1963, and by 1968,99% of the sewage had been diverted .. from the lake (Edmondson 1910). Al- though the data plotted in Fig. 3 show the .ot- . Muo,rop'uc . I....I....I...... I increase and decrease in nutrients and re- '033 1950 ,g60 '970 sulting biological changes, the rates of Fig. 3. Top: Yearly changes in average sum- change differ considerablyfor each param- mer values of three parameters in Lake Wash- eter.Chlorophyll a seems to be only slightly ington, Seattle, Washington. Below: Data trans- affected until 1961, whereas Secchi disk formed into trophic state index values. transparency shows a drastic decrease be- tween 1950 and 1955. Conversely, after sewage diversion in 1963, chlorophyll a TSI values based on transparency. The TSI shows a dramatic decrease, while there is valuespredicted by total phosphorus closely a 3-year lag before Secchi disk transpar- parallel the biological TSI values, adding ency changes noticeably. These discrepan- strength to the argument that phosphorus cies in rates of response are the result of was the key nutrient in determining the the inverserelationshipbetween chlorophyll biological trophic state of Lake Washing- concentration and transparency. Secchi ton. disk transparency is very sensitive to bio- mass changes at low concentrations, but Discussion is insensitive at high concentrations. If t The trophic index presented here has onlychlorophyllhad been measured during several advantages over previous attempts the 19505,it might have seemed that sig- at trophic classification. nificant changes in the lake did not occur The scale is numerical rather than no- until after 1961. When chlorophyll values menclatural, allowinga large number of in- are converted to TSI, however, they can dividual lake classes rather than three to be seen to be responding rapidly to enrich- five distinct ones. This allows sensitivity l ment, and the changes parallel those in the in describing trophic changes. The major 368 Cal'!$on trophic divisions have' a logical basis, the lake estimated. This should prove of namely the doubling of concentrations of value to groups interested in determining surface algal biomass, which should make how much nutrient abatement is necessary the trophic state classification more ac- to reach a desired trophic condition. ceptable theoretically. The index can be used for regional classi- Although the scale itself is constructed fication of all surface , including from a single parameter, the mathematical and . Any correlation with other parameters allows could be classified using the total phos- some latitude in selecting the best one for phorus index, which is essentially a predic- a given situation. The use of correlated tor of potential algal biomass. Hutchinson parameters also allows trophic comparisons (1969) suggested that lakes and their between lakeswhere different types of data drainage basins should be considered were collected in different studies. Calcu- as trophic systems, where a eutrophic lation of the index for more than one pa- system is one in which the potential rameter for a given lake also serves as an concentration of nutrients is high. The in- internal check both on methodology and dex allows the classificationof that poten- on assumptionsas to relationshipsbetween tial concentration for a watershed or reo parameters. gion, at least on the basis of phosphorus. The data used can be minimal or exten- Such a classification could develop an sive,depending on the level of accuracy de- awareness of regional patterns in trophic sired and the available. Secchi potentia~ and could then also allow regional disk values alone can give a trophic state trophic standards to be the basis of rational classification,information that can be col- management. lected even by nonscientistsin public-par- Finally, a trophic state index is not the ticipation programs at little expense (Sha- same as a water quality index. The term piro et al. 1975). If the survey is more quality implies a subjective judgment that extensive, data on chlorophyll and total is best kept separate from the concept of phospborus can provide supplementary or trophic state. A major point of confusion alternative index values. The index number with the existing terminology is that eu- gives both the public and the limnologist trophic is often equated with poor water a reasonablyaccurate impressionof a lake's quality. Excellent, or poor, water quality water quality. For the layman, the num- depends on the use of that water and the ber may have little meaning at first, but it local attitudes of the people. The definition can readily be transformed into Secchi of trophic state and its index should re- transparency, which is easily understood. main neutral to such subjective judgments, By analogy, the Richter scale has remaining a framework within which vari- meaning for people other than seismolo- ous evaluations of water quality can be gists. For the limnologist the index can made. The TSI can be a valuable tool for be an aid in communicationbetween him- lakemanagement,but it is alsoa valid scien- self and other . With only the tific tool for investigationswhere an objec- TSI value, a reasonable estimate can be tive standard of trophic state is necessary.I made of the Secchi disk transparency, hope that the index can serve as a standard chlorophyll, and total phosphorus. of trophic measurementagainst which com- The index can be used as a predictive parisons can be made between the many tool in lake-managementprograms. If the chemical and biological components of the mean total phosphorus after nutrient abate- lake system that are related to trophic ment can be predicted with loading-rate status. The result could be a more com- equations such as those of Vollenweider plete and dynamic picture of how these (1969,1976), then a new TSI can easily be components relate to one another and to calculated and the biological conditions of the lake ecosystemas a whole. -

Trophic state index 369

References POWERS,C. F., D. W. SCHULTS,K. W. MALUEG, R. M. BRICE,ANDM. D. SCHULDT. 1972. BEETON,A. M., ANDW. T. EDMONDSON.1972. Algal responses to nutrient additions in nat- The problem. J. . Res. ural waters. 2. . Am. Soc. Bd. Can. 29: 673-682. Limnol. Oceanogr. Spec. Symp. 1: 141-154. BREZONDC,P. L., ANDE. E. SHANNON. 1971. RODDE,W. 1969. Crystallization of eutrophi- Trophic state of lakes in north central Florida. Fla. Water Resour. Res. Center cation concepts in northern , p. 50- 64. In Eutrophication: Causes, conse- PubI. 13. 102 p. quences, correctives. NatI. Acad. Sci. Publ. c.uu.soN, R. E. 1975. Phosphorus cycling in a 1700. shallow eutrophic lake in southwestern Min- nesota. Ph.D. thesis, Univ. Minnesota. SAKAMOTO,M. 1966. by DILLON,P. J., ANDF. H. RxcLER. 1974. The phytoplankton in some Japanese phosphorus-chlorophyU relationship in lakes. lakes and its dependence on lake depth. Arch. LimnoL Oceanogr. 19: 767-773. Hydrobiol. 62: 1-28. EDMONDSON,W. T. 1970. Phosphorus, nitro- SCHELSa, C. L., L. E. F'ELDr,M. A. SANTIACO, gen, and algae in Lake Washington after di- ANDE. F. STOERMER.1972. Nutrient en- version of sewage. Science 169: 690-691. richment and its effect on phytoplankton pro- HUl'CHINSON,G. E. 1957. A treatise on lim- duction and species composition in Lake nology, v. 1. Wiley. Superior. Proc. 15th Conf. Res. -. 1969. Eutrophication: Past and pres- 1972: 149-165. ent, p. 17-26. In Eutrophication: Causes, SHAPIRO,J., J. B. LUNDQ\J1ST,ANDR. E. CARLSON. consequences, correctives. NatI. Acad. Sci. 1975. Involving the public in - Publ. 1700. an approach to communication. Int. Ver. KmCHNER,W. B., ANDP. J. DILLON. 1975. An Thear. Angew. Limnol. v.erb. 19: 866-874. empirical method of estimating the retention STEELE,J. H. 1962. Environmental control of of phosphorus in lakes. Water Resour. Res. in the sea. LimnoI. Oceanogr. 11: 182-183. 7: 137-150. LASENBY,D. C. 1975. Development of oxygen deficits in 14 southern Ontario lakes. LimnoJ. TYLER,J. E. 1968. The Secchi disc. Limnol. Oceanogr. 20: 993-999. Oceanogr. 13: 1-6. LAWSON,D. W. 1972. Temperature, trans- VOLLENWEIDER,R. A. 1969. Possibilities and parency, and phytoplankton productivity in limits of elementary models concerning the , Oregon. LimnoL Oceanogr. 17: budget of substances in lakes. Arch. Hydro- 410-417. bioI. 66: 1-36. MICHALSJC:,M. F., AND N. CoNBOY. 1972. -. 1976. Advances in defining critical Water quality evaluation-Lake Alert study. loading levels for phosphorus in lake eutro- Ontario Min. Environ. Rep. 23 p. phication. Mem. 1st. Ital. Idrobiol. 33: 53- MoYER,J. R., ANDR. L. THOMAS. 1970. Or- 83. ganic phosphorus and inositol in molecular size fractions of a organic mat- ter extract. Soil Sci. Soc. Am. Proc. 34: Submitted: 5 February 1975 80-83. Accepted: 18 November 1976

Announcement Pacific Section, American of Limnology and Oceanography, Inc. The Pacific Section will meet 12-16 June 1977 at San Francisco State University, San Francisco, California. A symposium on "The San Fran- cisco Bay" is scheduled for 13 June. Symposia on "Coastal " and " of western streams and rivers" are planned for 15 June.