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University Microfilms International 300 North Zeeb Road Ann Arbor, Michigan 48106 USA St. John's Road, Tyler's Green High Wycombe, Bucks, England HP10 BHR I I 78-10,140 YOUNG, Thomas Charles, 1946THE DWMMICS OF ACCUMULATION OF PHOSPHORUS BY THE SEDIMENTS OF THE LAKE SYSIBi OF THE WATER QUALITY MANAGEMENT PROJECT AT MICHIGAN STAIE UNIVERSITY. Michigan State University, Ph.D., 1977 Limnology ' 1 University Microfilms International, AnnArbor.Michigan48ioe THE DYNAMICS OF ACCUMULATION OF PHOSPHORUS BY THE SEDIMENTS OF THE LAKE SYSTEM OF THE WATER QUALITY MANAGEMENT PROJECT AT MICHIGAN STATE UNIVERSITY By Thomas C h arles Young A DISSERTATION S u bm itted to M ich ig an S ta te U n iv e r s it y in p a r t i a l f u l f i l l m e n t o f th e re q u ire m e n ts f o r th e degree o f DOCTOR OF PHILOSOPHY Departm ent o f F is h e r ie s and W i l d l i f e 1977 ABSTRACT THE DYNAMICS OF ACCUMULATION OF PHOSPHORUS BY THE SEDIMENTS OF THE LAKE SYSTEM OF THE WATER QUALITY MANA GE ME NT PROJECT AT MICHIGAN STATE UNIVERSITY By Thomas Charles Young The lake system of the Mi ch ig an State University Water Quality Management Project received secondary effluent from the wastewater treatment plant in East Lansing. Phosphorus dynamics in the sediments of Lakes 1 and 4 of the system were investigated in terms of transport of phosphorus to the sedi­ ments by sedimentation of seston, accumulation of phosphorus in the sediments, and partitioning of phosphorus in seston and sediments. Lake 1 had higher phosphorus loadings than Lake 4 and was dominated by phytoplankton, while Lake 4 was dominated by macrophytes. The absence of macrophytes in Lake 1 permitted resuspension of particulates from the lake bottom and resulted in rates of sedimentation of seston which were six times greater than those in Lake 4. Resuspension affected the pattern of phosphorus accumula­ tion in sediments. In Lake 4, phosphorus accumulation was greatest in shallow water since macrophytes minimized Thomas Charles Young resuspension. In Lake 1, accumulation was greatest in deep water and areas of eddy formation where less resuspension occurred. Phosphorus content of seston from Lake 4 averaged l,8l mg P/g and varied by insignificant amounts. Phosphorus in seston from Lake 1 was 3.49 mg P/g prior to and 20,27 mg P/g after a permanent increase in the phosphorus concentration of secondary effluent from an average of 1.4 to 4.1 mg P/1 which occurred as a result of a change in wastewater plant operation. Rate of sedimentation of phosphorus by seston was greater than the rate of phosphorus loading in both lakes. Most of the phosphorus transported to the sediments by seston in both lakes was bound to organic matter by adsorption. In sediments from Lake 1, most of the phosphorus was parti­ tioned by adsorption to organic matter which occurred predom­ inantly as an iron-organic complex. In sediments from Lake 4, most of the phosphorus was partitioned by adsorption to inor­ ganic iron colloids. Accumulation of phosphorus In sediments was greater at higher loading rates than lower rates, but growth of macrophytes permitted greater accumulation of phosphorus in sediments than phytoplankton at the loading rates observed In Lake 1. Macro­ phytes reduced oxygen demand on the sediments which permitted accumulation of iron-bound phosphorus. Loss of phosphorus from sediments of Lake 1 was associated with resuspension, while macrophyte growth accompanied losses from the sediments in Lake 4. Thomas Charles Young At the stage of development of the lake system at the time of this investigation, permanent accumulation of phosphorus in the sediments was 6.6 and 10.5 percent of incoming phosphorus to each lake. On the basis of these values, it is postulated that permanent accumulation of phosphorus by the sediments of this lake system will not be effective for withdrawing phos­ phorus from secondary effluent. ACKNOWLEDGMENTS I wish to thank Dr. Robert C. Ball, the chairman of my guidance committee, for the freedom to pursue my own course of study and for his guidance during the preparation of this manuscript. I wish to thank the other members of my guidance commit­ tee, Drs. Mackenzie L. Davis, Niles R. Kevern, Darrell L, King, and Clarence D. McNabb, of this manuscript. for their suggestions and criticisms A special expression of gratitude is due Dr, King for countless discussions of matters pertaining to limnology as a science and a career. I thank my wife, Suella, for her patience, perseverance, understanding, and participation during the period of our lives required for this work. I wish to thank the Institute of Water Research for sup­ porting this investigation by providing financial assistance, equipment, and personnel when required during certain phases of field and laboratory a ct i v i t i e s . ii TABLE OP CONTENTS Page INTRODUCTION ............................................. METHODS AND MATERIALS 1 .................................. 8 Description of the Study A r e a .................... Wastewater Plow History ........................... Primary Production ............................... S e d i m e n t s ........................................... S e s t o n ............................................. Methods of Chemical Analysis .................... Statistical M e t h o d s ............................... Loading Estimates .................................. 8 11 16 16 28 31 3** 35 RESULTS AND DISCUSSION .................................. ^2 Phosphorus Loading ............................... Primary Production ............................... S e s t o n ............................................. S e d i m e n t s ........................................... Process of Phosphorus Accumulation in S e d i m e n t s .................................... ^2 ^7 50 67 SUMMARY AND CONCLUSIONS 75 ............................... A P P E N D I X .................................................. 89 LITERATURE CITED 90 ......................................... iii LIST OF TABLES TABLES 1. Page Characteristics of East Lansing and MSU secondary effluent, April 1975 to October 1976 .................................................... 15 2. Sediment core sampling dates for Lake 1, 2, 3, and 4 of the Water Quality Management P r o j e c t , 1975-1976 ....................... 3. Loading of phosphorus to lake system May 1975 to October 1976 (g P / m 2-yr) .................. 4. Changes in dominant algal group, rate of sedi­ mentation of seston and seston content of phosphorus and organic carbon following introduction of unmodified secondary effluent, 1975-1976 64 Phosphorus accumulation in the sediments of the lake system, 1975-1976 ......................... 68 Phosphorus bound by iron and organic matter in sediment samples from Lake 1, May and September 1975 ....................................... 77 Phosphorus bound by iron and organic matter in sediment samples from Lake 4, April and June 1976 79 56. 7. 8. Accumulation, loading and sedimentation of phosphorus in Lakes 1 and 4 .......................... °0 Al. Monthly phosphorus loading to lake system, Michigan State University Water Quality Management Project, g P/ m 2 and kg P / l a k e ............ 89 Iv LIST OP FIGURES FIGURE 1. Page Lake System, Michigan State University Water Quality Management Project ........................ 10 2. Weekly volumes of secondary effluent introduced to the lake system and pumped to the spray irrigation site, Michigan State University Water Quality Management Project, from January 1975 through November 1976 ...........................13 3. Device used to obtain cores of lake sediment . . . 18 4. Location of sampling stations for sediment cores and sediment traps, Lake 1, Michigan State University Water Quality Management Project ... 20 Location of sampling stations for sediment cores and sediment traps, Lake 4, Michigan State University Water Quality Management Project ... 22 Location of sampling stations for sediment cores, Lake 2, Michigan State University Water Quality Management Project . . . . . ............. 24 Location of sampling stations for sediment cores, Lake 3> Michigan State Univeristy Water Quality Management Project ........................ 26 Sediment Trap, drawn in plan and side views, details in t e x t ........... : . . . . ............ '. 30 Comparison of measured and predicted monthly discharges of water from Lake 4, Michigan State University Water Quality Management Project ... 39 5. 6. 7- 8. 9. 10. Comparison of measured chloride concentrations with concentrations estimated by hydraulic bal­ ance, lake system, Michigan State University Water Quality Management Project, 1975 and 1976 ................................................ v FIGURE 11. Concentrations of total phosphorus in East Lansing effluent pumped to lake system, May 1975 through October 1976 . ...................... 12. Monthly loading of phosphorus to the lakes of the Michigan State University Water Quality Management Project, April 1975 through October 1976.. ............................................... 13- Concentration of total phosphorus in East Lansing effluent and lakes of the lake system, Michigan State University Water Quality Manage­ ment Project, May 1975 through October 1976 . . . 14. Average rates of sedimentation of seston, Lake 1, Michigan State University Water Quality Management Project, May 1975 through October ............................................... 1976 15* Average rates of sedimentation of seston, Lake 4, Michigan State Univeristy Water Quality Management Project, May 1975 through October 1976 ............................................... 16. Average rates of sedimentation of seston as a function of depth at Station 1 (near inlet), Station 2 (mid-lake), and Station 3 (near outlet), Lake 1, Michigan State University Water Quality Management Project ................ 17* Average rates of sedimentation of seston as a function of depth at Station 1 (near inlet), Station 2 (mid-lake), and Station 3 (near outlet), Lake 4, Michigan State University Water Quality Management Project ............... 18. Phosphorus partitioning in seston from Lake 1 and 4, Michigan State University Water Quality Management Projectj circle sections propor­ tional to percent and phosphorus bound by iron (Fe), calcium (Ca), organic carbon (OC), and unidentified (U) ................................. 19. Pattern of phosphorus accumulation in sediments of Lakes 1 and 4, Michigan State University Water Quality Management Project ............... Page FIGURE 20. Phosphorus partitioning in sediment samples from Lakes 1 and Michigan State University Water Quality Management Project; circle sections are proportional to percent of phos­ phorus bound by iron (Fe)» calcium (Ca), organic carbon (0C), and unidentified (U) . . . • vii 74 INTRODUCTION The Michigan State University Water Quality Management Project is a pioneering effort in wastewater recycling. Through application of scientific understanding of aquatic and terres­ trial ecosystems, the project strives to meet societal needs for wastewater disposal and desires for clean water. However, achievement of these goals requires a realistic management plan which cannot be derived from current knowledge of these systems. Mechanisms which bring about renovation of waste­ water in natural systems must be defined and assessed for inclusion in such a plan. Phosphorus is a wastewater component of concern, since it promotes aquatic plant growth. Thus, a major goal for the project is reduction of phosphorus concentrations by the system. In the lake system, biological uptake of phosphorus represents a temporary storage compartment, the size of which depends on standing crop. In contrast, permanent phosphorus removal can occur in lake sediments. Phosphorus in sediments has been studied by limnologlsts for the past 40 y e a r s . According to Hutchinson (1957), Einsele (1936, 1938) was the first to suggest the existance of a rela­ tionship between iron and dissolved phosphorus in hypolimnetic 1 2 waters. Mortimer (19^1, 19^2) observed release of phosphorus and iron when anaerobic conditions developed in sealed watersediment systems. Early interpretations of the iron-phosphorus association (Hutchinson, 1957; Ruttner, 1963) described a cycle of p r ec ip i­ tation and dissolution involving an hypothesized insoluble ferric phosphate and a soluble ferrous phosphate. The ferric compound was said to be formed under aerobic conditions and displaced to the sediments where reduction of the iron occurred, allowing loss of phosphorus by dissolution and diffusion. No direct evidence has been given for the formation of discrete ferric or ferrous phosphate compounds during annual phosphorus cycles in lakes (Armstrong et_ a l . , 1971). Golterman (1975) reported that Thomas (1965) demonstrated that ferric phosphate in activated sludge was not solubilized in passage through anaerobic digestion. Still, the ferric phosphate model has formed the basis for design of phosphorus removal facilities in wastewater treatment and has worked in practice (EPA, 1976). Currently, the lron-phosphorus relationship is thought to involve adsorption of inorganic phosphorus to oxides and hydrated oxides of iron in the water column (Stumm and Morgan, 1970; Stumm and Leckie, 1971; Golterman, 1975) as has been de mon­ strated under laboratory conditons (Gastauche et, a l . , 1963; from Syers et^ a^L., 1973). After reaching the sediments, two mechanisms have been postulated for the relationship between iron and phosphorus. Inorganic phosphorus was shown to be bound by amorphous iron 3 oxides and hydroxides in calcareous and non-calcareous lake sediments using analytically defined phosphorus fractionation procedures (Williams et al,, 1971a; Williams et al., 1971b; Williams et^ a l ,, 1971c; Shukla et^ a l ,, 1971)* The second mechanism involved formation of a humic-iron-phosphorus complex, wherein iron was bound to phosphorus and this complex was bound secondarily to a decay-resistant organic molecule (Golterman, 1975). Binding of phosphorus by calcium has been shown to depend on the amount of calcium in the lake water. Golterman (1973) presented evidence for hydroxyapatite control of phosphorus concentrations in Lake Geneva. Stumm and Morgan (1970) and Stumm and Leckie (1971), based on solubility, considered hydroxy­ apatite to control the distribution of phosphorus between water and sediments in most natural lakes. Lee (1970), however, did not believe that hydroxyapatite played a major role in the chemistry of phosphorus in water or sediments (from Syers et, a l ., 1973). Williams et al, (1976) presented evidence that apatite phosphorus was an important contributor to the sedimen­ tary phosphorus of surficial sediments of Lake Erie, but con­ cluded that it was due to erosion from terrestrial sources. Stumm and Leckie (1971) demonstrated the conversion of calcite to hydroxyapatite slow. but indicated the process was very Williams and Mayer (1972) presented evidence that dia- genic formation of hydroxyapatite in deep sediments of Lake Ontario was widespread in that lake. Williams et aJ. (1971a) found little evidence for apatite in non-calcareous sediments, but gave evidence that it formed a major portion of inorganic phosphorus in calcareous sediments (Williams et a l ., 1971b). White and Wetzel (1975) showed a direct relationship between phosphorus and calcium carbonate in seston from a hardwater lake. In this same lake, Otsuki and Wetzel (1972) demonstrated coprecipitation of phosphorus with calcium carbonate using radioisotope methods. Zoltek (1976) analyzed data concerning pH and phosphorus concentration in wastewater treated with lime for phosphorus removal. He interpreted his results to mean octacalcium phos­ phate solubility controlled phosphorus concentration rather than that of hydroxyapatite or co-precipitation with calcium carbonate. Adsorption of dissolved phosphorus by sediment samples taken from the Roanoke River and Chesapeake Bay was studied by Carritt and Goodgal (195*0* Their results suggested phosphorus sorption reduced regeneration of phosphorus under anaerobic conditions. Harter (1968) studied phosphorus adsorption by eutrophic lake sediments and concluded that two mechanisms were involved: one involved a tightly bound aluminum phosphate, and a second involved a more loosely bound iron phosphate. Williams et al. (1970) found non-calcareous lake sediments adsorbed and retained more added organic phosphorus than 5 calcareous sediments, and that the adsorption reactions were not reversible over the period of observation. Shukla et al. (1971) confirmed these results and found that chemical removal of the hydrated iron oxide gel from the sediments eliminated the phosphorus adsorption capacity of both calcareous and noncalcareous sediments, They stated that the adsorption capacity was inversely related to the calcium carbonate content of the calcareous sediments, Patrick and Khalid (197*0 studied adsorption of phosphorus by terrestrial soils under aerobic and anaerobic conditions. Their results showed anaerobic conditions permitted greater adsorption from solutions higher in phosphorus, and greater desorption to solutions lower in phosphorus than occurred unden aerobic conditions. They interpreted their results as meaning the hydrated iron oxide gel gained in surface area during anaerobic periods .as a result of chemical reduction of iron. Adsorption of phosphorus to aluminum clays in natural systems was considered important by Stumm and Leckie (1971). However, a study of phosphorus adsorption by standard clay minerals (Edzwald et a l . , 1976) demonstrated that acid extrac- table iron and calcium content of clays was more closely related to phosphorus adsorption capacity than acid extractable alumnium or the aluminum:silicon atomic ratio. After sophisticated statistical manipulation, phosphorus fractions in sediment samples taken from several lake types (Williams et a l ., 1971c) showed no relationship between total 6 phosphorus and any alumninum fraction. However, extractable aluminum was related to organic phosphorus, Williams et^ al. (1971c) found no relationship between organic carbon and total phosphorus in sediments, but found that organic phosphorus was closely related to organic carbon. A similar finding was made by Sommers et al. (1972) who con­ cluded that organic phosphorus levels in sediments were related to organic matter dynamics, rather than differences in the kinds of organic phosphorus present, Golterman (1975) believed that phosphorus reaching the sediments by particulate sedimentation was organic-bound and that mineralization resulted in secondary binding by a mineral component, probably iron hydroxide. However, he presented no data to substantiate this hypothesis. Based on radioisotope studies, Hutchinson and Bowen (1950) concluded that sedimenta­ tion of phytoplankton was responsible for vertical displacement of phosphorus in stratified l a k e s . Autolytic release of phosphorus by sinking phytoplankton was shown to recycle up to 80 percent of algal phosphorus prior to cell movement out of the epillmnion (Golterman, However, the phosphorus 1973)* content of growing algae was shown to depend on that of the growth medium and percent losses would reflect these conditions (Sievers, et al. (1971) 1972; Young, 1972). Foree showed losses of 50 to 60 percent of cell phos­ phorus under prolonged aerobic and anaerobic conditions. They concluded that the extent of phosphorus loss was dependent on 7 the length of degradation period and the initial nutrient concentration of the algal culture. Thus, there is less autolytic regeneration of phosphorus from cells grown in lakes under low phosphorus concentrations that in lakes with high phosphorus concentrations. Phosphorus in lake sediments occurs as a result of inter­ actions between the biology, physics, and chemistry of the lake and its watershed. The current state of understanding of sedimentary processes involving phosphorus permit qualitative prediction of phosphorus binding mechanisms in sediments. How­ ever, these mechanisms lack quantitative details which relate them to interactions with lake biota and phosphorus loading. Consequently, prediction of permanent losses of phosphorus to the sediments is unreliable wit h present knowledge. This investigation endeavors to characterize and quantify the mechanisms involved in permanent and temporary storage of phosphorus in the sediments of the lakes of the Water Quality Management Project. The approach employed to meet these objectives involved consideration of levels of phosphorus loading, and growth and decay of dominant aquatic plants as influences on (1) sedimentation of seston as a means for trans­ porting phosphorus to the sediments, phorus in the sediments, (2) accumulation of ph os ­ (3) partitioning of phosphorus in seston and sediments, and (4) the dynamics of the sediments of the lake system as a compartment for phosphorus. METHODS AND MATERIALS Description of the Study Area The Michigan State University Water Quality Management Project provided the field setting for this investigation. A detailed description of the project plan, facilities, and objectives can be found elsewhere (Institute of Water Research, 1976). A brief description is given here. The facility con­ sists of an activated sludge wastewater treatment plant, which is part of the East Lansing municipal treatment works; a trans­ mission line, for transport of treated wastewater; four lakes in series, for detention of the treated wastewater; and a spray Irrigation area, consisting of a woodlot and open fields. The lake system, illustrated in Figure 1, has a combined surface area of 16 ha, and each lake has a mean depth of 1.8 m. The lakes are unprotected from wind due to the lack of surrounding trees and terrain contour, with the exception of the west end of Lake which is protected by a road grade. Fluorescent dye studies of water movement in these lakes during May, 1976, showed each lake was well mixed with mixing times of 10 to 20 percent of detention time. The circulation pattern of each lake depended on wind direction and had the following characteristics: (1) wind shear produced a surface current 8 Figure 1: Lake System, Michigan State University Water Quality Management Project FIGURE 1 JOLLY (meters) LAKE 2 INFLOW 3-31 ha T OUTFLOW LAKE 4 LAKE 3 INTERSTATE 11 which ran in the same direction as the wind; (2) at the lee shore, a subsurface return current formed which ran windward; (3) the subsurface return current originated at lee shoreline ang ul ar it i es . Wastewater Flow History The lake system was filled first during the fall of 1973, and this water was allowed to stand until the summer of 197^. Pumping was resumed for a short period during the fall of 197^ at the nominal rate of 1.9 X 103 m 3/day in April, (0.5 M G D ) . Beginning 1975, the lake and spray systems were ready for con­ tinuous operation, and water was taken from the East Lansing Wastewater Treatment Plant at a rate of approximately 1.9 X 103 m 3/day (0.5 MGD). Hydraulic loading to the first lake was greater than that to the other lakes during this period, since water for irrigation was taken from the outlet of Lake 1, during 1975Lake system inflow and irrigation volumes for 1975 and 1976 are shown in Figure 2. Flow to the lake system was inter­ rupted for approximately two weeks beginning about the end of June, 1975, to permit a change in pump location from the old to a new clarifler at the wastewater treatment plant. then resumed and continued through October, In December, Pumping 1975* 1975, East Lansing began operation of a new wastewater treatment facility; and from April to about mid-May, 1976, water from the new facility was pumped to the lake system. All of the secondary effluent pumped to the lake system from Figure 2: Weekly volumes of secondary effluent introduced to the lake system and pumped to the spray irrigation site, Michigan State University Water Quality Management Project, from January 1975 through November 1976 FIGURE 2 t— • i— i— i— i— i— i— i— i i i— r LAKE I INFLOW ▼ SPRAY IRRIGATION * t j J F MAMJ i:;i( J A S O N D 1975 J F M A M J J A S O N 1976 in the fall of 1973 to mid-May of 1976, had been treated with ferric chloride and organic polymer to remove phosphorus. By that time part of the old East Lansing wastewater facility had been put into operation by Michigan State University, and it was operated without a phosphorus removal step. Beginning about mid-May, water coming to the lake system was secondary effluent with its normal complement of phosphorus, and for the remainder of this investigation, sufficient secondary effluent was pumped to provide approximately 1,9 X 10 3 m 3/day (0.5 MGD) of water to the lake system exclusive of water for spray irrigation. During 1976, irrigation water was taken from the transmission line, upstream from the inlet to Lake 1 which resulted in occasional back-siphoning of water from Lake 1. Given in Table 1 are mean values and coefficients of vari­ ation (CV) for selected water quality parameters for the secon­ dary effluent pumped to the lake system, during periods of flow. While these data do not indicate it directly, the raw wastewater treated at the East Lansing facility is relatively weak. East Lansing has no industry besides small retail businesses, and wastewater from Michigan State University receives treatment from the East Lansing plant. As a result, the East Lansing plant treats wastewater consisting, principally, of sanitary domestic waste and urban runoff. A detailed characterization of East Lansing municipal wastewater, before, during, and after treatment, can be found in other sources (Institute of Water Research, 1976). Table 1. Characteristics of East Lansing and and MSU secondary effluent, April 1975 to October 1976 Time Period 1975 1-30 Apr* mean CV 1 May to 5 Jul* mean CV 13 Jul to 26 Oct* mean CV 1976 12 Apr to 18 May* mean CV 27 May to 31 Oct** mean CV Total Phosphorus (mg P/1) Total Iron (mg Fe/1) Total Calcium (mg Ca/1) 1.05 0.11 65 4 0.48 0.29 0 38 1.28 0.04 1.38 0,85 0.14 0.92 49 97 0 21 24.6 2.18 7.68 0.03 1.58 0.49 0.25 0.67 74 82 0 19 18.4 1.64 8.00 0.04 1.38 0.37 0.34 0.92 85 8 0 04 12.0 — 7-97 0.07 4.22 0.29 0.30 0.42 73 87 0 07 * East Lansing Secondary Effluent ** Michigan State University Secondary Effluent Filterable Residue (mg/1) 47.3 6.6 0.59 pH 7-32 7.41 0.03 16 Primary Prod uc ti on Studies of primary prod uc ti on in Lake 1 and 4 were made concurrently with this invest ig a ti on (Schloesser, duction by phytoplankton, macrophytes, 1975)* Pro­ and asso ci at ed epiphytes was estim at ed by oxygen me as urements taken at dawn, dusk, and daw n in p l e x i gl as s enclosures. I d e nt if ic at i on and counting of p h y t o p l a n k t o n were p e rf o rm ed u sing mem br an e filtration t e c h ­ niques, and c h l o r o ph yl l- a was me asured by acetone extraction, corrected for p h a e o p h y t i n s . Macrophyte s t a n d i n g crop was esti­ mated in all lakes by McNabb e £ al. (1975, 1 9 7 6 ). Sediments Sediment cores were obtained in plastic tubes with the device i l lu st ra te d in Figure 3 w h i ch was built from a prototype designed by Robert P. Glandon, a graduate student in Fisheries and Wildlife at Michgan State University. S ediment cores were obtained f r o m Lake 1 and 4 at the p er ma ne nt ly marked sampling stations s hown in Figures 4 and 5* Sediment cores from Lakes 2 and 3 w e r e taken from the locations shown In Figures 6 and 7• Dates for core sampling are given In Table 2. Cores w er e returned to the laboratory intact, and the w at er o ve r l y i n g each was aspirated to w i t h i n 1 cm of the s ed im en t - w a t e r interface. Eac h core was e x a m in ed visually and depth of ac cu m u l a t i o n of sediment over the na ti ve determined. clay seal was Coring tubes were marked with a felt tipped pen Indicate d e m a r c a t i o n of the core into three or more strata: (1 ) an u pp er stratum, the ac cu mu l a t i o n zone; (2 ) a middle to Figure 3: Device used to obtain cores of lake sediment 18 51 X 51 cm pine shaft eye , bolt 1*3 cm dowel ' e eye vbolt No. 10 rubber stopper hose ^ c la rn p g x ^ me plexiglass * i E o O to coring tube 4 * 4 cm ID FIGURE 3- Figure 4: Location of sampling stations for sediment cores and sediment traps, Lake 1, Michigan State University Water Quality Management Project 20 INFLOW FROM EAST LANSING LAKE I 1*8 m CONTOUR (Mean Depth) OUTFLOW to Lake 2 FIGURE H 0 ■ 25 50 75 ■_____________________«_____________________ i — METERS 100 i Figure 5: Location of sampling stations for sediment cores and sediment traps, Lake 4, Michigan State University Water Quality Management Proj ect LAKE 4 OUTFLOW INFLOW l-8-m CONTOUR (Mean Depth) 0 50 100 * ■ — 1 METERS 150 - ■ ■ 200 — 1 figure 5 Figure 6 Location of sampling stations for sediment cores, Lake 2, M i c h ig an State University Water Quality Management Project LAKE 2 INFLOW ro I* 8 m CONTOUR (Mean D ep th ) 25 50 METERS OUTFLOW to Lake 3 FIGURE 6 75 100 Figure 7 Location of sampling stations for sediment cores, Lake 3, Michigan State University Water Quality Management Project N LAKE 3 INFLOW i OUTFLOW to Lake 1- 8m CONTOUR (M ean Depth) FIGURE 7 4 rv> cr> Table 2. Sediment core sampling dates for Lake 1, 2, 3, and M of the Water Quality Management Project, 1975-1976 Lake 1 Lake 2 Lake 3 Lake 4 2, 3 May 1975 9, 19 May 1975 16 September 1975 9 October 1975 10 January 1976 1 April 1976 2 June 1976 30 June 1976 30 June 1976 11 June 1976 25 October 1976 25 October 1976 25 October 1976 2 September 1976 25 October 1976 28 stratum, a transition zone, which often contained small amounts of upper stratum material carried down by the shearing action of coring; and (3 ) a lower stratum, which was clay from the lake seal. The cores were frozen and sectioned with a metal saw. The sections were dried for approximately 48 hours at 110°C, cooled, and weighed. Dried sections were hand ground by mortar and pestle to pass a Number 35 Standard Sieve (maximum diameter 0.5 mm), and stored in glass containers. Ground sections of sediment cores were chemically analyzed and accumulation of phosphorus was determined by the amount of phosphorus in the sectioned cores. For each sampling station the value for accumulation was calculated as the difference between the total phosphorus in the core and the total which would have been present had the levels of phosphorus in upper and transition strata been equal to that of the underlying clay seal. Seston Seston was collected in sediment traps, one of which is illustrated in Figure 8 . Six 50 ml glass centrifuge tubes were held upright by means of an inverted plastic bucket which had holes drilled in the bottom to hold the tubes securely. The buckets were fitted with lead weights at the open end to pro­ vide negative buoyancy. An inverted bucket assembly was sus­ pended at depths of 0 .5 , 1 .0 , and 1.5 m from eyebolts at the corners of a 2 m equilateral wooden triangle which was anchored Figure 8 : Sediment Trap, drawn in plan and side views, details in text 30 Ptan .Yis-M PLASTIC BUCKET (Submerged) CENTRIFUGE TUBES 51X10 2 CM ANCHOR ROPE PINE BOARDS WATER LEVEL 2 M EYE BOLT ANCHOR ROPE JOXUJ CENTRIFUGE PLASTIC TUBES BUCKET Side View FIGURE 8 31 from two sides and allowed to float on the surface. These triangles plus bucket assemblies were positioned in Lakes 1 and 4 in open water at the locations indicated in Figures 4 and 5. The tubes of each bucket were assigned to one of three replicate groups for sampling. For each s a m p l i n g * two tubes of a specified replicate group at each depth were removed and replaced w i t h fresh tubes. Replicate groups were sampled in order which allowed estimation of sedimentation of seston over long overlapping periods. The long periods were found neces­ sary to provide sufficient material in a manageable number of samples. Seston samples were returned to the laboratory and examined qualitatively for algae, macrophyte fragments, macroinvertebrates, and detritus. zooplankton, Volume measurements after c entrifugation at 1000 g for 10 minutes were taken. The solids from both replicates were combined and dried for 48 hours at 1 1 0 ° C , cooled, and weighed. Samples were ground by hand using a mortar and pestle and stored in glass containers. Methods of Chemical Analysis Standard analytical methods were employed for the d eter­ mination of phosphorus, seston samples. iron, calcium, and carbon in core and Total carbon and carbonate carbon were deter­ mined gravimetrically by the wet oxidation and acid extraction procedures described by Allison et al. Moodie (1965). (1965), and Allison and The digestion reagent used in the carbonate digestion was modified to 0.5 N HC1 from 2 N H2 S0i,, and the 32 FeSOi, • 7 H 20 recommended as a reductant was not included. A paired data analysis showed no significant difference between the results obtained by the two methods (P > 0.1), for esti­ mating inorganic carbon. Total elemental analyses for phosphorus, iron, and calcium involved acid decomposition of the sample using a HNO3-H2SO1* digestion, as described in Standard Methods (APHA, 1971) for heavy metals in polluted waters. Care was taken to avoid excessive fuming of S03 during digestion to avoid volatiliza­ tion of phosphorus (Maxwell, 1968). The digestate was diluted to approximately 50 ml with H 20, boiled, and filtered through Number 3 Whatman filter paper, supported by a Buchner funnel. Digestates from the carbonate carbon analysis were filtered in a similar manner for determination of acid extractable phos­ phorus, iron, and calcium, The total element digestions render a near complete decom­ position of the samples, leaving a residue consisting chiefly of quartz sand and some occluded metal oxides, including iron (Maxwell, 1968). Percent recoveries of incremental additions of phosphorus, iron, and calcium, and their standard errors were 101.4 ± 0.7, 100.9 ± 9 .6 , and 99*9 ± 2.7* respectively, for the total element analysis. The results of recovery trials for iron and calcium using the acid extraction procedure were 97.9 ± 2.6 and 101.9 ± 1.6 percent, respectively. Recovery of phosphorus by the acid extraction procedure was not performed. Wentz and Lee (1969) and later, Cowen and Lee (1976) described an acid extraction procedure for "plant available" 33 phosphorus, similar to that used here, with the exception of the heating step. The latter authors suggested that their procedure extracted calcium-bound phosphorus, much of the iron and aluminum-bound phosphorus, surface-bound or adsorbed phos­ phorus, but not phosphorus occluded in oxides of iron, or appreciable phosphorus from hydrolysis of carbon-oxygenphosphorus linkages of organic phosphorus. Further, Cowen and Lee (1976) failed to show effective acid hydrolysis of inosi­ tol (phytic acid) phosphate, after boiling for 1 hour at 100°C with 0.09 N H 2S O4 . Wentz and Lee (1969) found their cold extraction had no hydrolytic action on adenosine monophosphate and minimal hydrolysis of calcium phytate. Sommers et a l . (1972) found that extraction with 1 N HC1 (no time or tempera­ ture given) removed both in calcareous and non-calcareous sedi­ ments. Mehta et al. (195*0 found no hydrolysis of organic phosphorus in terrestrial soil samples extracted with 12 N HC1 after heating for 10 minutes on a steam table. While no recovery experiments with organic phosphorus were conducted in the present investigation, the results reported by others indicate that most of the phosphorus in the acid extractable fraction was physically or chemically bound inorganic phos­ phorus and that discrete organic phosphorus contributed little to this fraction. A colorimetric finish was used for both total and extractable phosphorus determinations. The procedure employed the Automated Colorimetric Ascorbic Acid Method (EPA, 197**)• These analyses were performed by the technical staff of the Michigan 34 State University Institute of Water Research Water Quality Laboratory using a Technicon Auto-Analyzer, All iron and calcium final determinations were obtained by atomic absorption spectroscopy according to standard procedures (EPA, 1974). Virtually all physical and chemical data for lake water and secondary effluent were furnished by the Water Quality Laboratory, Institute of Water Research. Statistical Methods Statistical reduction of data was by analysis of variance. Univariate split-plot designs were employed for analysis of phosphorus accumulation and seston sedimentation to remove correlations resulting from sequential sampling of the same locati on s. Phosphorus partitioning in sediment and seston samples was estimated by multiple regression analysis. It was assumed that the phosphorus in these samples was bound to either iron, calcium, or organic matter by physical mechanisms occlusion or adsorption, or by chemical mechanisms ionic or covalent bonding or chemisorption. regression, such as such as By multiple the amount of phosphorus In sediments and seston was compared to amounts of Iron, calcium and organic carbon. When phosphorus levels were related to levels of these other elements, it was concluded that a causal relationship existed and was a result of binding of phosphorus by the related ele­ ments . 35 Amounts of phosphorus which we re shown by the analysis to be bound by either iron, calcium or organic carbon in samples of sediment and seston were calculated from the regression equation. Average amounts of phosphorus bound by each element were expressed as percentages of total phosphorus or extractable phosphorus in the samples. Phosphorus not bound by any of these elements was assumed to be equal to the constant te rm In the regression equation, and where signifi­ cant (P < 0.05), this term was included as an unidentified form of p h o s p h o r u s . Loading Estimates Hydraulic loading during the period 1 May 1975 to 31 October 1976 was estimated for each lake by stepwise applica­ tion of the hydrologic balance given by the following equa­ tion. V in + ^a tm ” V out + V exf Where: V in = Volume of w at er flov/ing to a lake, m 3 V atm = Volume of w a te r gained or lost to the atmosphere, m 3 V Qut ” Volume of w a t e r flowing from a lake, m3 V r = Volume of water lost through exfil­ tration, m 3 36 Recorded volumes of flow to the lake system from East Lansing were used as inflow volume ) for Lake 1. Outflow volume (Vout)» calculated from the balance equation, was used as V in for Lake 2 on the next step. Water for spray irriga­ tion was taken from the outflow of Lake 1 in 1975, and from the inlet pipe to Lake 1 in 1976. In either case, the calcu­ lation was modified for the irrigation volume for Lake 1 cal­ culations. Atmospheric gains and losses (Va^ ) were estimated from data reported by the U.S. Weather Bureau, Capitol City Airport, Lansing, Michigan. Precipitation was taken directly from monthly totals, and evaporation was estimated after an empirical method suggested by Pair and Geyer (1963). Exfll- tration volume (Vexf) was calculated as the difference between estimated and measured total discharge from the lake system for 1976. The estimate of V exf for the system was 0.11 to 0.22 cm/day; and for loading calculations, a median of 0.165 cm/day was used. The results of a direct estimate of lake seal exfiltration gave a value of 0.18 cm/day (Bahr et a l ., 1977). Assumptions required for use of the hydrologic balance equation were: (1 ) exfiltration was constant and uniform; (2) meterologic data from the U.S. Weather Bureau, Capitol City Airport, Lansing, Michigan, represented conditions at the Water Quality Management Project site; and (3) lakes were always full. Hydraulic loading was verified two ways. The first method was a comparison of estimated and measured volumes of discharge from the lake system. The results of this comparison 37 are illustrated in Figure 9* The mean difference between measured and calculated values was not significant (P > 0.5), indicating a strong relationship, and that calculated flows closely predict field measurements. The second verification involved use of the hydraulic loadings in a chloride mass balance for each lake, and com­ parison of predicted chloride concentrations with those obtained by analysis of water samples. gave the results shown in Figure 10. The chloride balance The hydrologic balance permitted prediction of chloride concentration with a stand­ ard error of estimation of 9 percent of the mean measured concentration for 1975 data, and of 5 percent for 1976 data. Additional assumptions required for the chloride balance were: (1 ) the lakes were completely and instantaneously mixed; chloride was conservative; (2 ) (3 ) irrigation water taken upstream from Lake 1 was secondary effluent, with no back siphoning; and (4) the volume and chloride content of runoff entering the lakes were neglegible. Phosphorus loading was estimated as the product of flow estimates and measured concentrations of phosphorus in East Lansing effluent and the lake system. Figure 9: Comparison of measured and predicted monthly discharges of water from Lake M, Michigan State University Water Quality Management Project FIGURE 9 7 6 MONTHLY DISCHARGE VOLUME MEASURED 5 m3 XIO4 4 3 2 r = 0 -9 3 7 p < 0-01 \ 0 I 2 3 4 PREDICTED m3 X I 0 4 5 6 7 Figure 10: Comparison of m e a s u r e d chloride concentrations wit h c o n ce nt ra ti on s e s t i m a t e d by hydraulic balance, lake system, M i c h i g a n State Univ e rs it y Water Quality M a n a g e m e n t Project, 1976 1975 and 1975 r= 0 - 7 4 130 120 m MEASURED mg Cr/I 100 90 80 70 80 90 100 PREDICTED, 110 mg FIGURE 10 A 1975 • 1976 120 CP/I 130 140 RESULTS AND DISCUSSION Phosphorus Loading Phosphorus concentrations in East Lansing effluent are shown in Figure 11. From May, 1975, through May, 1976, concen­ trations averaged 1.45 mg P/1. During this period iron chloride was used for phosphorus removal in the East Lansing plant. Iron additions were discontinued after May, and from June through October, 1976, phosphorus concentrations averaged 4.09 mg P/1. Phosphorus loadings to individual lakes are summarized in the Appendix and illustrated In Figure 12. Time intervals for these values are approximately one month, either 4 or 5 weeks, since East Lansing flow data were in weekly summaries. Down­ stream lakes received less phosphorus than lakes immediately upstream in the system due to phosphorus retention by succeed­ ing lakes, and loss of volume from exfiltration and evapora­ tion. Annual loadings for each lake of the system are summar­ ized in Table 3• Loading values for the lakes of the Water Quality Manage­ ment Project can be compared with those which Vollenwieder C1968 ) recommended to avoid eutrophic conditions. As a guide­ line, Vollenwieder set the critical level at 0.10 g P / m 2-year for lakes with a mean depth less than 2 m. 42 This value is less Figure 11: Concentrations of total phosphorus in'East Lansing effluent pumped to lake system, May 1975 through October 1976 FIGURE 11 60 with phosphorus I no phosphorus removal removal EAST LANSING 5 0 PHOSPHORUS, mg P / I EFFLUENT 40 New Plant Old Plant 30 20 No Flow 00 O 1975 N D J F M A ----------------- +------------------ M J 1976 J A S O Figure 12: Monthly loading of phosphorus to the lakes of the Michigan State University Water Quality Management Project, April 1975 through October 1976 FIGURE 12 I Lake I H Lake 2 mmm Lake o v.v m W.'.W.W mm Isiilisii oJ m m •mmm .W.! mm Q. wm m m m o> .v.v. LOADING IM iriV IH V W I -Cr MONTHLY o\ 0*021 Table 3. Loading of phosphorus to lake system May 1975 to October 1976 (g P / m 2-yr) 1976 1 17.4 •=r -=r • 1975 00 Lake 2 6.45 20.37 3 1.94 6.93 4 0.89 0.98 than the annual loading received by any lake in the system during this investigation. The lakes in this study each received sufficient phosphorus to be classed as eutrophic by V o l l e n w i e d e r 's criteria. Phosphorus concentrations in successive lakes were less as loading diminished as shown in Figure 13. in Lake 1 averaged 0.86 mg P/1 from May, Total phosphorus 1975, through July, 1976, and 2.68 from August through October, 1976. the average for the entire per io d was 0.05 mg P/1. In Lake 4 Lakes 2 and 3 showed concentrations intermediate to those of Lakes 1 and 4. Primary Production The primary producer communities of Lakes 1 and 4 were dissimilar. Lake 1 was dominated by phytoplankton (diatoms, unicellular green algae, cryptomonads, and filamentous green algae. and blue-green algae), Macrophytes (Elodea canadensis and Potamogeton f o l lo su s) were present in significant numbers in Lake 1 only during late summer, 1975, when a combined Figure 13: Concentration of total phosphorus in East Lansing effluent and lakes of the lake system, M i c h i g a n State University Water Quality M a n agement Project, May 1975 through October 1976 ^9 FIGURE 13 60 EAST LANSING LAKE I LAKE 40 2 LAKE 3 LAKE 4 30 20 TOTAL PHOSPHORUS, mg P / I 50 EFFLUENT 00 M J J A S O N D J F M A M J J A S O 1975 1976 50 standing crop of 54 g dry w e i g h t/ m2 was observed (McNabb et_ al*» 1975). In contrast, Lake 4 was dominated by macrophytes (principally El o d e a ) in 1975* and 1976, with maximum standing crops of 208 and 499 dry w eight/m2 , in each year, respectively (McNabb et a l ., 1975, 1976). Phytoplankton chlorophyll-a was higher in Lake 1 than In Lake 4. During the period 5 May to 1 October 1975, chlorophyll-a ranged between 2.7 and 52.1 m g / m 3 in Lake 1, with an average value of 17.4 m g / m 3. In Lake 4 values ranged from 0.0 to 5-9 m g / m 3, with an average of 2.5 m g / m 3 (Schloesser, 1975). Gross primary production by phytoplankton as determined by oxygen measurements was higher in Lake 1 than in Lake 4 during this period. Lake 1 averaged 1.97 g C/m2-day, while Lake 4 averaged 0.69 g C/m2-day (Schloesser, 1975). Seston Microscopic examination of seston from Lake 1 revealed the presence of phytoplankton and zooplankton. However, seston from Lake 1 showed more decomposition than that from Lake 4, and the predominant component was unidentifiable detrital material. Lake 4 seston contained detritus as well, usually fecal pellets. Seston from Lake 4 predominantly contained macrophyte fragments and identifiable phytoplankton, which included: Cosmarium sp., Scenedesmus sp., Chlorella sp., Spirogyra sp., Mougeotia sp., Gomphosphaerium sp., Chroococcus « sp., Merismopaedla sp., Splrulina sp., Oscillatorla sp. 51 Clay and other inorganic materials, which were scoured from the lake edge and bot to m by wind-driven currents, were present in greater amounts in seston from Lake 1 than Lake 4. Analysis of the relationship between the volume and dry weight of seston showed that the weight of a volume of wet seston from Lake 1 was twice that of an equal volume from Lake 4. Regression coefficients relating seston dry-weight to volume were O . M ± 0.02 g/ml g/ml ( P <0.001) ( P <0.001) for Lake 4. for Lake 1 and 0.22 ± 0.03 Organic content of seston from the two lakes was similar, because production and sedimenta­ tion of phytoplankton in Lake 1 tended to balance clay from resuspension. Average content of organic carbon in seston from Lakes 1 and 4 was 72.8 and 79-7 m g C/g. Relative differences in amount of resuspension between Lakes 1 and 4 were estimated by assuming that the principal source of organic carbon in seston was sinking or resuspended phytoplankton in both lakes. The ratio of phytoplankton production to sedimentation of organic carbon in seston averaged 0.85 in Lake 1 and 1.71 in Lake A value less than 1.0 for this ratio indicates either phytoplankton were not the source of organic carbon in seston, organic material was occurring. or resuspension of settled Since phytoplankton were the dominant primary p roducer group in Lake 1, and a major contri­ butor to seston in Lake M, these values indicate resuspension was at least twice as extensive in Lake 1 as in Lake 4. Movement of fluorescent dye showed the extent to which macrophytes reduced current velocities and resuspension in 52 the lakes of the Project. A standing crop of 150 g dry w e i g h t / m 2 of macrophytes, which were 98 percent Elodea, plus 200 g dry w e i g h t / m 2 of filamentous algae (McNabb et aJL. 4 1976), reduced current velocities in Lake 2 to one-half of those observed in Lake 1 under similar wind conditions but with no macrophytes. Prom differences in macrophyte abundance between Lakes 1 and 4, It is concluded that the greater resuspension measured in Lake 1 was due to greater current velocities resulting from low macrophyte density as compared to Lake 4. Rates of sedimentation of seston were higher in Lake 1 than Lake 4, due to greater resuspension and production of phytoplankton in Lake 1, and suspended solids in water e n te r­ ing Lake 1 from East Lansing. The average value for all samples was 31-8 g / m 2-day for Lake 1 and 4,9 g / m2-day for Lake 4. Low standing crop of macrophytes during the spring of 1975 in Lake 4 as well as Lake 1 permitted edge erosion and resuspension in both lakes. Erosion and resuspension during that period resulted in the highest rates of sedimentation observed. Rates of sedimentation of seston averaged for all depths and locations are given in Figures 14 apd 15 and il lus­ trate the high rates of sedimentation which occurred that spring. In April of that year, the standing crop of m a c r o ­ phytes in Lake 1 was too low to quantify, while Lake 4 had a combined macrophyte-filamentous algae biomass of 31 g dry weight/m2 . Figure 1*1: Average rates of sedimentation of seston, Lake 1, Michigan State University Water Quality Management Project, May 1975 through October 1976 RATE - day g/ m SEDIMENTATION SESTON LAKE I 50 40 95 % Confidence Interval 20 M J J A S O N D J F M A M J 1976 1975 FIGURE 14 J A S O Figure 15: Average rates of sedimentation of seston, Lake Michigan State University Water Quality Management Project, May 1975 through October 1976 RATE g / m2 - day 95% 4 Confidence Interval SESTON SEDIMENTATION LAKE M J J A S O N D J F M A M 1976 1975 FIGURE 15 J J A S O 57 S us pe nd ed solids in East Lansing effluent entering Lake 1 i nc reased sedime nt at io n throughout Lake 1 be tween April and June of 1975. Peak effluent residue coincided with peak sedi­ me nt at io n in Lake 1, d u r i n g June of that year and occurred w h e n the East Lansing effluent had a filterable residue as hi gh as 305 m g / 1 . S ed im e n t a t i o n rates were greater near the inlet of Lake 1 (Figure 4) and the outlet to Lake 4 (Figure 5) than at other locations w i t h i n each lake. Figures 16 and 17 illustrate v e r ­ tical prof il es of average rate of sedimentation at different locations in each lake. In Lake 1 near the inlet, Station 1, rates of sedimentation at 1.5 m averaged 250 percent more than those at any other location. In Lake 4 near the outlet, S t a ­ tion 3 , r ates of se dimentation were 30 pe rcent greater at all depths than those m e a su r ed at other locations. The h i g h e r values found near the inlet to Lake from s us p e n d e d solids in East Lansing effluent, 1 resulted and the cir­ culation p a t t e r n which depe nd ed on wind direction. Dye trac­ ing studies revealed f o rm at io n of an eddy in the inlet of Lake 1 (Figure 4) during periods w h e n wind was fro m the west or northwest. Suspended solids In the East L a n s i n g effluent entered this eddy and settled to the bottom, w h i ch resulted in higher s e d i m en ta ti on rates near the inlet. H i g h e r rates of se dimentation of seston at of Lake 4 (Figure 5) r e s u l t e d from deeper w a t e r w ater c i r c u l a ti on at that location. the outlet and greater M a c r o ph yt es did not grow to the s ur face in deeper water near the outlet, and it is Figure 1 6 : Average rates of sedimentation of seston on a function of depth at Station 1 (near inlet), Station 2 (mid-lake), and Station 3 (near outlet), Lake 1, Michigan State University Water Quality Management Project FIGURE 16 LAKE I • Station ■ Station A Station 95% Confidence Interval 1-5 10 DEPTH, m Figure 17: Average rates of sedimentation of seston a function of depth at Station 1 (near inlet), Station 2 (mid-lake), Station 3 (near outlet), Lake H t Michigan State University Water Quality Management Project FIGURE 17 95% Confidence Interval >» 0 T> 1 5 CM E s C7> LAKE 4 SESTON SEDIMENTATION RATE 8 • Station ■ Station 2 A Station 3 05 DEPTH, m I 62 presumed that this resulted in reduced competition and per­ mitted more phytoplankton production and sinking. Additionally, winds from the prevailing west and southwest set up windward subsurface currents, which caused resuspension of bottom deposits. Resuspended material was carried to the sampling location, since macrophytes were not present to retard water movement. Transport of phosphorus to sediments by sedimentation of seston was greater in Lake 1 than Lake , Average rates of transport by seston were 0,171 g P/m2-day in Lake 1 and 0.005 g P/m2-day in Lake H. The difference between rates in Lake 1 and Lake 4 resulted from greater sedimentation of seston and greater amounts of phosphorus in seston in Lake 1 than Lake 4. The phosphorus content of seston averaged 1.81 mg P/g in Lake ^ and did not change proportionately to changes in phosphorus concentration of lake water which occurred between sampling periods. Prior to the flow of unmodified secondary effluent in May, 1976 (Figure 12) phosphorus content of seston from Lake 1 did not change between sampling periods in proportion to changes in lake concentration. However, after the flow from East Lansing began, the concentration of phosphorus and phosphorus content of seston increased in Lake 1. Phosphorus content in seston from Lake 1 averaged 3*^9 mg P/g prior to the flow of unmodified secondary effluent and 20.27 mg P/g after the flow began. Phosphorus content of samples taken from different depths was similar within both lakes. 63 Increased phosphorus content of seston in Lake 1 resulted in part from greater amounts of phytoplankton in seston, as shown by changes in the organic carbon content of seston after the flow began. Presented in Table 4 are data concerning dominant algal type, rate of sedimentation of seston, and phosphorus and organic carbon content of seston, during the period after the flow began, As diatoms replaced filamentous algae, sedimentation of seston increased, as did the phosphorus and organic carbon content of seston. When diatoms gave way to other phytoplankton, sedimentation of seston decreased, but phosphorus and organic carbon content continued to increase. These data indicate phytoplankton quality as well as quantity influenced levels of phosphorus in seston, and modified rates of transport of phosphorus to sediments. Most of the phosphorus transported to the sediments of Lakes 1 and 4 by sedimentation of seston was bound by organic matter, and the principal binding mechanism was adsorption. Partitioning of total and the extractable fraction of phos­ phorus by iron, calcium, and organic matter is illustrated in Figure 18 for seston samples from the two lakes. The importance of adsorption as a mechanism for binding phosphorus to settleable particulate matter is shown by the amounts of extractable phosphorus in seston from both lakes. Extractable phosphorus, which was mostly adsorbed to organic matter averaged 92 percent of all the phosphorus in seston from Lake 1 and 74 percent of that in samples from Lake 4. Table 4. Changes in dominant algal group, rate of sedimentation of seston and seston content of phosphorus and organic carbon following introduction of unmodified secondary effluent, 1975-1976 Period Apri1-May June July-August ■SeptemberOctober Dominant Algal Group Filamentous Algae Diatoms Unicellular Green and Cryptomonads Green and Blue-Green Rate of Seston Sedimentation g/m2-day Seston Phosphorus mg P/g Organic Carbon mg C/g 12.8 3.17 75.9 20.8 15-34 91.7 17.5 17.42 121.3 16.1 26.1 144.9 Figure 18: Phosphorus partitioning In seston from Lake 1 and M ichigan State University Water Quality Management Project; circle sections proportional to percent and phosphorus bound by iron (Fe), calcium (Ca), organic carbon (OC), and unidentified (U) 66 FIGURE 18 TOTAL EXTRACTABLE PHOSPHORUS PHOSPHORUS oc OC 66 % 5*69 mg P/g 6*16 mg P /g LAKE I oc Ca 25% OC 75% 1*34 mg P/g 1*82 mg P/g LAKE 4 67 Total phosphorus in seston from Lake 4 occurred predom­ inantly In an unidentified form, while extractable phosphorus was bound predominantly by organic matter. Considering the small number of samples of seston which were analyzed from Lake 4 (20), this discrepancy Indicates total phosphorus was bound predominantly by organic matter, but that the variability in the amount of non-extractable phosphorus which was bound by organic matter, relative to the amount of organic matter pre­ sent, was too great to allow resolution of the state of total phosphorus as efficiently as that of extractable phosphorus alone. Sediments Measurements of amounts of phosphorus which accumulated in sediments of the lake system showed a gradient of declin­ ing accumulation through the sequence of lakes (Table 5)• Lake 1 had the greatest amount of accumulated phosphorus, Lake 4 had the least, and Lakes 2 and 3 were intermediate to these. The effects of lake inlet location, macrophyte beds, currents, and depth of water resulted in the patterns of accumulation of phosphorus illustrated in Figure 19 for Lakes 1 and 4. While Lakes 2 and 3 were as essential to the results of this investigation as Lakes 1 and 4, time requirements did not permit a detailed study of all lakes. Lakes 2 and 3 were sampled to determine amounts of phosphorus which accumulated in sediments, but the sample size was not sufficient to describe patterns of accumulation in these lakes. Table 5. Lake Phosphorus accumulation in the sediments of the lake system, 1975-1976 Date of Sampling Number of Samples Phosphorus Accumulation g P/m2 ± S-* kg P/lake V 1 3 16 10 2 2 25 1975 1975 1976 1976 1976 1976 15 17 17 17 5 5 2 30 Jun 1976 25 Oct 1976 3 30 Jun 1976 25 Oct 1976 4 9 9 1 11 25 May Sep Jan Jun Sep Oct May Oct Apr Jun Oct 1975 1975 1976 1976 1976 * Standard error of mean ± 1.63 ± 2.04 ± 1.79 ± 1.36 ± 1.41 ± 2.82 349.87 598.15 584.07 433.35 563.50 482.16 4 4 8.30 ± 3.81 10.13 ±2,69 275.44 336.00 3 3 6.93 ±1.51 4.73 ± 2.80 303.04 206.88 4.3 4.5 4.3 5.9 4,5 214.14 222.41 213.65 294.24 224.10 15 17 17 17 5 10.67 18.25 17.82 13.21 17.18 14.70 ± ± ± ± ± 0.41 0.41 0.41 0.41 0.62 Figure 19: Pattern of phosphorus accumulation in sediments of Lakes 1 and *1, Michigan State University Water Quality Manage­ ment Project 70 LAKE LAKE I 4 ■ 18-7 gP/m2 5*6 gP/m1 H 14-0 gP/m2 3 0 gP/m2 ■ 12-9 gP/m2 11 II '8 gP/m2 INLET LAKE I INLET ^ LAKE 0 L. 4 100 _l__ 200 i_ METERS FIGURE 19 300 71 In Lake 1, more phosphorus accumulated in shallow-water sediments near the inlet than in other, areas. The accumula­ tion near the inlet was greater due to the combined effects of suspended solids entering in the East Lansing effluent, and the eddy which formed in the inlet cove. As discussed earlier, these factors allowed greater amounts of phosphorus to be carried to the bottom by sedimentation of seston near the inlet than at other locations. Accumulation of phosphorus in Lake 1 was least in shallow water around the southern two-thirds of the lake due to the scouring action of subsurface, wind-driven currents. Resus­ pended phosphorus from shallow-water sediments was deposited in deep water, where resuspension was less effective. As Indicated earlier, rooted macrophytes were not abundant in Lake 1, which resulted in more resuspension in Lake 1 than in Lake 4 with its heavy aquatic weed b e d s . In Lake 4, more phosphorus accumulated in shallow rather than deep-water sediments. This pattern resulted from the occurrence of heavy beds of macrophytes which grew to the surface in shallow areas before doing so in deeper water. The effect of these plants was to reduce water movement, which hindered resuspension and allowed deposition in shallow areas. Phosphorus partitioning occurred by different mechanisms in the sediments of the two lakes. In Lake 1, organic-bound phosphorus was the main form retained in sediments and occurred as phosphorus adsorbed to organic matter. In Lake **, inorganic phosphorus predominated and occurred as phosphorus adsorbed to 72 inorganic iron. Partitioning of phosphorus by iron, calcium, and organic matter in sediment illustrated in Figure samples from Lakes 1 and 4 are 20. Phosphorus in sediment samples from Lake 1 was bound predominantly by organic matter which occurred as an ironorganic complex. Partitioning of the total phosphorus in sediments of Lake 1 showed most of the phosphorus as an organic bound form. However, partitioning of the extractable phos­ phorus, which was 88 percent of the total, indicated most of the phosphorus was bound by iron by adsorption. Based on the occurrence of high amounts of iron and organic matter with high levels of phosphorus and the degree of relationship found between iron and organic matter ( P < 0.001) in sediment samples from Lake 1, it is concluded that most of the phosphorus retained by the sediments of Lake 1 was bound by adsorption to an iron-organic complex. The predominant form of phosphorus retained by sediments in Lake 4 was iron-bound. cent of the total and iron colloids. matter. Extractable phosphorus was 66 per­ occurred mainly adsorbed to inorganic Little phosphorus was found adsorbed to organic However, some phosphorus was present as discrete organic compounds as shown by the occurrence of organic-bound phosphorus in the partitioning of total phosphorus. From this analysis, it is concluded that phosphorus adsorbed to inorganic iron colloids was the predominant form of phosphorus in sedi­ ments of Lake 4. Figure 20: Phosphorus partitioning in sediment samples from Lakes 1 and Mi chigan State University Water Quality Management Project; circle sections are proportional to percent of phosphorus bound by iron (Fe), calcium (Ca), organic carbon (OC), and unidentified (U) 74 FIGURE 20 TOTAL EXTRACTABLE PHOSPHORUS PHOSPHORUS oc Ca OC Fe 137. 0*92 mg P/g 1*04 mg P/g LAKE I OC 57o oc 68 7o 61 7o 0*50 mg P/g 0*33 mg P/g LAKE 75 Process of Phosphorus Accumulation in Sediments Data concerning sedimentation and accumulation of phos­ phorus in sediments, phosphorus components of seston and sedi­ ments, and composition of primary producer communities provide a mechanism to account for the presence and state of phosphorus in sediments of the lakes of the Water Quality Management Project. When phytoplankton dominate primary production, algal biomass sinks to the sediments and decomposes by the activi­ ties of bacteria and macroinvertebrates. When oxygen levels in accumulated sediments become insufficient to satisfy aerobic decomposition, anaerobic conditions and lower pH values occur. Autolysis, bacterial action, and ingestion by macroinvertebrates release phosphorus from phytoplankton and detritus. Organic material produced by algal decay and resistant to further decomposition adsorbs the phosphorus released by decomposers. Phosphorus in sediments under these conditions exists as organic phosphorus of undecayed organic matter and is also bound to organic and inorganic detritus by adsorption. At pH values less than 6-7, organic matter adsorbs iron as well as phosphorus (Koenigs, 1976). When the sediment surface is aerobic and pH is greater than 7, iron, bound to decayresistant organic matter, desorbs to form hydrated ferric oxides. These inorganic iron colloids adsorb phosphorus and increase the capacity of the sediments to bind phosphorus. The pH dependent adsorption of iron to organic matter is a mechan­ ism by which sediments are buffered against loss of iron as 76 conditions change from aerobic to anaerobic, thus retaining phosphorus binding capacity if aerobic conditions return. By retaining biomass in the water column, macrophytes reduce oxygen demand in sediments and assist in creatine con­ ditions which favor accumulation of phosphorus by adsorption to inorganic iron. However, dur in g periods of macrophyte decomposition, the amount of organic material in sediments increases. If sufficient oxygen is not available for decom­ position, anaerobic conditions occur and result in loss of iron-bound phosphorus and an increase in phosphorus bound to organic matter by adsorption. Examples from Lake 1 and 4 illustrate the mechanisms of phosphorus accumulation In sediments. From May to September, 1975, a change occurred in the primary producer community of Lake 1. In May, macrophytes were too sparse for quantifica­ tion, but developed a standing crop of 56 g dry weig ht /m 2 between late July and mid-August. The lowest of daily oxygen measurements during this period was 2.2 mg 0 2/l and occurred during July. Oxygen was not found lower than 5.2 mg 0 2/l during August or lower than 9-4 m g 0 2/l during September. Accumulation of phosphorus Increased by 7.6 g P / m 2 during this period. Data concerning phosphorus partitioning in sediment samples taken during May and September are given in Table 6. Phosphorus in the sediments changed from an organic-bound to an iron-bound form, and some of the phosphorus adsorbed to organic ma tt e r was lost, presumably resorbed by inorganic iron. These data support the hypothesis that growth of macrophytes Table 6. Sample Date May September Phosphorus bound by Iron and organic matter In sediment samples from Lake 1, May and September 1975 Phosphorus Fraction Phosphorus Content (mg P/g) Iron-Bound (?) Organic-Bound (?) Total 0.93 4.2 74.4 Extractable 0.76 0.0 89.4 Total 1.13 71.1 28.9 Extractable 0.87 100.0 — 78 V assists accumulation of phosphorus by reducing oxygen demand on sediments, which allows accumulation of phosphorus by inor­ ganic iron. In Lake 4, a period of declining macrophyte biomass occurred between April and June, 1976. During the decline, daily measurements of dissolved oxygen averaged 10.8 mg 02/1 * Sediments accumulated 1.6 g P / m 2 of new phosphorus between early April and mid-June, Phosphorus forms, given in Table 7* showed an increase in organic phosphorus re' ■'tive to other components, no change in phosphorus adsorbed to organic matter, and a gain in inorganic iron-bound phosphorus. These observa­ tions support the hypothesis that aerobic decomposition of macrophytes assists accumulation of phosphorus as organic phosphorus in decay-resistant organic matter and phosphorus adsorbed to inorganic iron colloids. With reduced concentrations of phosphorus in downstream lakes, total loadings of phosphorus decreased (Figure 12) and less phosphorus accumulated In sediments (Table 5) through the lake sequence. The correlation between phosphorus loading and accumulation indicates the lake system responded to higher loading rates by increased accumulation in sediments. However, measurements of accumulation of phosphorus in the sediments of Lake 1, taken after the lake system began to receive unmodified secondary effluent, showed accumulation of phosphorus did not increase in proportion to the Increased loading. Phosphorus accumulation, loading and sedimentation of phosphorus by seston are summarized in Table 8. Accumulation of phosphorus in Table 7• Sample Date April June Phosphorus bound by Iron and organic matter in sediment samples from Lake 4, April and June 1976 Phosphorus Fraction Phosphorus Content (mg P/g) Iron-Bound (58) Organic-Bound (58) Total 0.51 72.3 20.5 Extractable 0.34 60.9 12.2 Total 0.48 66.7 28.5 Extractable 0.30 88.2 11.8 Table 8. Accumulation, loading, and sedimentation of phosphorus in Lakes 1 and 4 Sediment Sampling Date Phosphorus Accumulation (g P/m2) Change in Accumulation (g P/m2 ) Phosphorus Loading Average Daily (g P/m2-day) Total (g P/m2) Total Phosphorus Sedimentation by Seston (g P/m2) Lake 1 May, 1975 10.7 +7.6 0.09 11.7 30.2 September, 1975 18.2 -0.4 0.05 5.5 4.9 January, 1976 17.8 -4.6 0.02 3.1 6.2 June, 1976 13.2 +4.0 0.22 20.1 26.6 September, 1976 17.2 -2.5 0.36 21.7 25*1 October, 1976 14.7 +4.1 0.12 62.1 93.0 May, 1975 to October, 1976 Lake 2 May, 1975 4.3 +0.2 0.005 0.7 0.37 October, 1975 4.5 -0.2 0.001 0.2 0.84 April, 1976 4.3 +1.6 0.002 0.1 0.45 June, 1976 5.9 -1.4 0.008 0.9 1.97 October, 1976 4.5 +0.2 0.004 1.9 3.55 May, 1975 to October, 1976 81 sediments Increased periodically rather than continuously and alternated with periods of loss. The intervals of gain and loss correspond to activities in the aquatic plant community and not to changes in phosphorus loading. In Lake 1, increased accumulation in sediments was found only during summer months. A greater increase occurred during the summer of 1975, at a lower rate of phosphorus loading, than the summer of 1976. The increase of 1975 was in an iron- bound form and was associated with growing macrophytes as dis­ cussed earlier. During the following summer, phosphorus load­ ing increased over two-fold, with the flow of unmodified secondary effluent, but the increase in accumulation of phos­ phorus in sediments was half as great as that which occurred the previous summer. The smaller increase in accumulation occurred as organic-bound phosphorus, was associated with pro­ duction of phytoplankton, and was less than that of 1975 pre­ sumably because of decay of algae and release of phosphorus. A comparison of phosphorus loading, accumulation in sediments, and primary producers for 1975 and 1976 indicates that quality of primary production had a greater effect on accumulation of phosphorus in sediments than level of loading. Increased accumulation of phosphorus in the sediments of Lake k occurred only during the spring of 1976 and was not related to increased loading. From April to June of that year, phosphorus was stored in sediments as inorganic iron-bound phosphorus and organic phosphorus, and coincided with aerobic decay of macrophytes. 82 Periods of loss of phosphorus accumulation were associated with aquatic plant activities in both lakes. The greatest of three periods of loss in Lake 1 (Table 8) occurred during the spring of 1976. At mid-winter, filamentous green algae were present at the sediment-water interface. After the ice left the lake at the end of February and water temperatures began to rise, these algae began to increase and float to the surface in mats. Based on high ash and phosphorus content found in samples of algae taken during this period (McNabb et al., 1976; King, personal communication), it is hypothesized that mats of filamentous algae trapped resuspended particles which con­ tained phosphorus, and thus, were indirectly responsible for the loss of phosphorus from sediments. The greater loss of phosphorus from sediments of Lake 4 occurred during the summer of 1976 and was associated with an increase in standing crop of E l o d e a . Phosphorus loading during the period was insufficient to provide more than 55 percent of phosphorus present in plant biomass, based on analysis of samples of plant tissue taken during the period (King, personal communication). Accordingly, it is concluded that the remain­ der of the plant phosphorus was derived from phosphorus accumu­ lation in sediments and was a major cause of loss of accumulation of phosphorus from sediments in Lake 4. Transport of phosphorus to the sediments by sedimentation of seston increased as loading increased. As shown in Table 8, sedimentation of sestonic phosphorus was greater than phos­ phorus loading for most periods in Lakes 1 and Thus, loss of phosphorus from sediments,as a result of resuspension, 83 decomposition of organic matter, and aquatic plant production reduced the capacity of Lakes 1 and 4 to store phosphorus in sediments, rather than insufficient rates of transport in particulate form. During the first year of this investigation, iron was added for phosphorus removal at the East Lansing wastewater treatment plant. Increased accumulation of phosphorus in the sediments of Lake 1 during the summer of 1975 in an iron-bound form indicates the iron in East Lansing effluent enhanced the pro­ cess of phosphorus accumulation In sediments during that summer. However, this investigation has shown the mechanism of phos­ phorus accumulation in sediments in the lake system to be dependent on the composition of the primary producer community. Accordingly, it is concluded that the macrophyte production which occurred in Lake 1 during 1975 resulted in conditions which permitted utilization of iron in East Lansing effluent for retaining phosphorus in the sediments of Lake 1. SUMMARY AND CONCLUSIONS The lake system of the Water Quality Management Project showed an Impressive capacity to reduce aquatic plant nutrients In wastewater during this Investigation, Secondary effluent entering the lake system contained 3 to 4 milliequivalents of carbonate-bicarbonate alkalinity and was super-saturated with carbon dioxide; 20 to 25 mg/1 total nitrogen, mostly as nitrate; and 1 to 5 mg/1 total phosphorus. Plant utilization of these nutrients had a broad impact on water quality. R educ­ tion of carbon dioxide concentration, as a result of photo­ synthesis and atmospheric loss, caused pH to increase from an average of 7,5 in East Lansing effluent to values exceeding 10.5 occasionally. Increased pH resulted In higher carbonate concentrations which precipitated with calcium and caused a loss of Inorganic carbon from the water. As nitrogen was converted from the nitrate form in the East Lansing effluent to proteins and amino acids by the aquatic plants, and finally to ammonia through decomposition of these plants, elevated pH shifted the ammonia-ammonium equilbrium toward ammonia and resulted in the loss of large quantities of ammonia nitrogen to the atmosphere. Phytoplankton and macrophytes removed phosphorus from the water through uptake and growth and transported It to 84 85 lake sediments. In the sediments phosphorus was released through d e c o m po si ti on and returned to the w a t e r or accumulated as ads o rb ed or organic phosphorus. By fa ci litating ecological interactions be t w e e n biology, physics, and chemistry, the lake t system r e d u c e d phosphorus and nitrogen concentrations to less than 5 p e rc en t of those in East Lansing effluent. This in v es ti ga ti on was conducted w hi le the lake system was m a t u r i n g ecologically. As the in ve s ti ga ti on progressed, aquatic p lant communities evolved and e stablished dominance, deposition of sediments occurred and covered the native clay bottoms, and a pool of organic detritus formed w h i c h did not consolidate wi th sediments, but was resusp en de d frequently as seston. As phosphorus was channeled from East Lansing efflu­ ent into these compartments, phosphorus was retained by the lake system. This in ve s t i g a t i o n has attempted to clarify the mechanisms u n d e rl yi ng the dynamics of phosphorus In the sediments of the lake system by r e l at in g levels of phosphorus loading and dominant aquatic plant growth and decay to (1) sedimentation of seston as a means for transporting phosphorus to the sedi­ ments, (2) a c cu mu l a t i o n of phosphorus in the sediments, and (3) p a r t i t i o n i n g of phosphorus in sediments and seston. The pres en c e or absence of m acrophytes a ffected the rate of se di m e n t a t i o n of seston and the p at tern of a cc um ulation of phosphorus in lake sediments. Sedimen ta ti on of seston was greater in Lake 1, which was dominated by phytoplankton, b ecause w i n d - d r i v e n currents had the capacity to resuspend 86 and redistribute particulate matter from lake bottoms, in the absence of macrophytes. In Lake 1, phosphorus accumulated in sediments in greater amounts near the outlet and near the inlet since resuspension of phosphorus was less effective in deeper t water and in the inlet eddy. In Lake 4, where macrophytes were abundant, resuspension was reduced and greater amounts of phosphorus accumulated in the sediments of areas with heaviest beds of macrophytes. The phosphorus content of seston was higher at the higher levels of phosphorus loading in Lake 1 than in Lake 4. How­ ever, in Lake 1, the phosphorus content and rate of sedimenta­ tion of seston increased or decreased as changes in phytoplank­ ton dominance occurred with diatoms resulting in greater rates of sedimentation and lower phosphorus content of seston than other groups of algae. Rates of phosphorus loading to both lakes were less than the rates of transport of phosphorus to lake sediments by sedimentation of seston. Amounts of phosphorus which had accumulated in the sedi­ ments of the lake system were greater at higher levels of phosphorus loading than at lower levels. However, accumulation of phosphorus In sediments at the higher loading levels of Lake 1 was greater when macrophytes were part of the aquatic plant community than when they were absent. Growth of macrophytes rather than phytoplankton increased amounts of phosphorus accumulation in sediments by reducing the demand for oxygen in sediments and allowing accumulation of iron-bound phosphorus. 87 Transport of phosphorus to the sediments of Lakes 1 and 4 occurred principally through partitioning of phosphorus by organic matter, either as phytoplankton or organic detritus, while phosphorus in the sediments was partitioned to either * organic or inorganic matter. In Lake 1, where phytoplankton dominated primary production, adsorption of phosphorus to organic matter predominated in sediments, while In Lake 4, with abundant macrophytes, adsorption of phosphorus to inorganic iron was the principal form. Storage of phosphorus In sediments was seasonal and largely temporary in Lakes 1 and 4, whether storage occurred by parti­ tioning to either an organic or an inorganic form. loss alternated with periods of gain in both lakes. Periods of Resuspen­ sion resulted In the greatest loss of phosphorus from the sedi­ ments of Lake 1, while direct uptake by growing macrophytes resulted in the greater loss of phosphorus from the sediments of Lake 4. At the stage of ecological development attained in Lakes 1 and 4 at the time of this Investigation, amounts of phosphorus permanently retained by sediments were small compared to total amounts entering the lakes. Prom May, 1975* to October, 1976, accumulation of phosphorus in the sediments of Lakes 1 and 4 amounted to 6,6 and 10,5 percent of phosphorus loading to each lake (Table 8), On the basis of data collected during this investigation, It is postulated that retention of phosphorus by the sediments of the lake system of the Water Quality 88 Management Project Is not an effective means for permanently withdrawing phosphorus from secondary effluent. « APPENDIX APPENDIX Al. M onthly phosphorus loading to lake system, M i ch i g a n State University W a ter Quality Ma na g e m e nt Project, g P/m2 and kg P/lake Time Interval* Lake 1 g P/m2 kg P/lake Lake 2 g P/m2 kg P/lake Lake 3 g P/m2 kg P/lake Lake 4 g P/m2 kg P/lake 1975 13 4 1 29 3 31 28 Apr May Jun Jun Aug Aug Sep 1 10 31 28 2 30 4 Apr May May Jun Aug Aug Oct 3 31 28 2 30 27 25 May May Jun Aug Aug Sep Oct 0.2 2.5 2.3 1.8 5.1 3 -3 2.2 1976 to 9 t o 30 t o 27 to 1 to 29 to 3 t o 31 May May Jun Aug Aug Oct Oct 1 .4 1.7 7.2 5.0 7.9 12.8 8.9 to to to to to to to 7.8 83.0 75.6 58.6 4.2 45.0 0.04 0.19 0.12 0.14 0.7 0.5 0.3 1. 9 8.9 5.1 6.0 29.3 21.4 13-0 0.03 0.13 0.07 0.04 0.19 0.27 0.15 1. 6 6.5 3 -7 2.0 9.3 13.6 7.6 25.5 24.8 43.2 55.6 196.2 178.7 150.2 0.2 0.07 0.25 0.28 2.0 3.1 1.0 8.9 0.05 0.02 o ’.06 0.05 0.13 0.41 0.26 2.4 1.2 3.1 2.3 6.5 20.4 12.7 26.6 11.0 45.8 73-7 0.1 0.9 0.8 0.3 1. 4 1.5 1.4 47.4 55.3 237.5 164.5 257.7 418.7 293.2 0.8 0.7 1. 3 1. 7 5.9 5- 4 4 .5 166.1 108.1 ■ F o u r o r f i v e c o n t i n u o u s w e e k s , d i s c u s s e d I n t e xt . 30.2 50.6 3.3 11.1 12.2 85-7 136.3 45.2 LITERATURE CITED LITERATURE CITED Allison, L.E., W.B. 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