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The Propagation of Sunlight And THE PROPAGATION OF SUNLIGHT AND THE SIZE DISTRIBUTION OF SUSPENDED PARTICLES IN A MUNICIPALLY POLLUTED OCEAN WATER Thesis by Lee Louis Peterson In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology Pasadena, California 1974 (Submitted January 15, 1974) TO BLAINE iii ACKNOWLEDGMENTS This study was performed under the direction and inspiration of Professor Wheeler North. He taught me to work in the ocean, monitored my research and provided crucial guidance in writing my thesis. Timely criticism and technical advice from Professor Sheldon Friedlander is deeply appreciated. His support and encouragement during my years at Caltech provided incentive for successful completion of my work. Professor James Morgan reviewed my research and suggested valuable improvements in presentation of the results. I am especially grateful for his interest and participation in student life. Professor Bruce Murray patiently served on all of my examining committees. Professor Norman Brooks encouraged my work and progress. Professor Seibert Duntley, from the Scripps Institution of Oceanography, graciously consented to participate in the final dissertation exam. A computer program for calculating the propagation of sunlight in ocean water was written by Dr. Warren White. Ed Myers filtered and analyzed suspended ocean particulates for carbon isotope ratios and percent organic carbon. A computer program, written by Arthur Jensen, was used to lV calculate statistical parameters. Joe Devinny, Peter Kirkwood, and Ed Myers at times arranged their schedules so that their work and mine could be performed on the same field trip. Steve Heisler and George Jackson provided helpful criticism and comment. Elton Daly and Tom Stephan were responsible for the very difficult task of maintaining the boats and other marine equipment. I am grateful to Bob Douglas and Gerald Johnson of TRW Systems, Redondo Beach,for their hospitality in offering the use of their laboratory, Coulter Counter, transmissometer, and water sampling equipment. It has been a privilege to be one of Marjorie Connely's "boys". A heartfelt thanks for her expert typing of the text and figures of my thesis. Kind assistance was received from Angela Bressan in the Registrar's Office, Rod Casper in the Library, and Ruth Toy in the Graduate Office. Whit and Judy Howland were especially kind and helpful through difficult times. Andrea Muir, a very lovely lady, provided many helpful suggestions regarding style and content of the thesis. Constant support and encouragement were received from my parents, Louis and Marie, during all of my years at Caltech. The research and the student's livelihood were supported by grants from the United States Public Health Service and TRH Systems. v ABSTRACT Waste discharge by the Los Angeles County Sanitation District (LACSD) affects sunlight in the ocean. Increased sunlight attenuance affects productivity and changes in ocean surface color could be useful for monitoring dispersal. Temperature, sunlight irradiance in five colors, light beam attenuance, and particle size distributions were simul~ taneously measured as a function of water depth. A limited number of samples were analyzed by a co~worker for particu­ late percent organic carbon and particulate carbon isotope ratio. Background field stations included Catalina, Dana Point, and Rocky Point. Stations in the vicinity of the LACSD outfall at Whites Point represented a dispersing sewage field. The most significant result was that pollutants decreased the optical albedo of ocean water, increasing the extinction of sunlight irradiance as a function of optical depth. Additional findings were that 1) pollutants decreased euphotic zone depths by as much as 60 percent (depending upon particle concentrations), 2) water surface color spectra indicated that pollutants increased light absorption at short wavelengths (violet, blue and green), 3) the average particle concentration in polluted waters was twice that of background waters, 4) the LACSD discharge caused a bimodal increase in vi particle numbers as a function of particle size: there was a dramatic increase for particles less than 1.5 microns and a secondary increase at 8 microns, 5) assuming real particle refractive indices (no light absorption by particles), scattering by natural and sewage particles was maximum be­ tween particle diameters 3 and 8 microns, 6) calculations assuming complex refractive indices (absorbing particles) indicated that light absorption by sewage particles was maximum for particles less than 1.5 microns in diameter, and 7) heavy (high specific gravity) particles had lower percent organic carbon and a lower carbon isotope ratio. vii TABLE OF CONTENTS Title 1. Introduction 1 2 . Background and Theoretical Development 10 2.1 Introduction 10 2.2 Sunlight Propagation 12 2.2.1 Downwelling Irradiance Data 12 2.2.2 The Euphotic Zone 22 2.2.3 Surface Ocean Color 28 2.3 Particle Properties 39 2.3. 1 Scattering and Absorption 39 2.3.2 Size Distributions 46 2.3.3 Carbon Isotope Composition 50 3. Procedures and Apparatus 53 3.1 Field Work 53 3.2 Laboratory Work 56 viii Chapter Title 4 . Experimental Results 62 4.1 Introduction 62 4.2 ~unlight Propagation in Polluted 64 and Natural Waters 4.2.1 Field Station Locations 64 4.2.2 Sunlight Irradiance Data 66 4.2.3 Depth of the Euphotic Zone 86 4.2.4 Surface Ocean Color 91 4.2.5 Sunlight Irradiance as a Function 94 of Ocean Optical Depth 4.3 Particle Properties in Polluted and 99 Natural Waters 4.3.1 Size Distributions 99 4.3.2 Vertical Distributions 109 4.3.3 Optical Densities 109 4.3.4 Scattering and Absorption 112 4.3.5 Physical Density, Percent 118 Organic Carbon, and Carbon Isotope Ratio 5 • Summary 124 Appendix A. Sunlight Propagation Model-­ 130 Preliminary Results Appendix B. Particle Size Distributions 144 (Tables) Notation 164 References 167 ix LIST OF FIGURES Figure Title Page 1-1 Photo-mosaic of sewage field from the 3 Los Angeles County outfall. Along~ shore drift. Infrared color by Wheeler North. December 30, 1972. 1-2 Photo-mosaic of sewage field from the 4 Los Angeles-County outfall. Seaward drift. Infrared color by Wheeler North. January 6, 1973 Historical charts of the Palos Verdes 6 coastline, showing gradual disappearance of kelp beds. Kelp areas drawn in black. Only two adult plants could be found here in summer, 1967. Average sewage dis­ charge rate for each year given in MGD (32,42). 2-1 Downwelling irradiance profiles (previous 13 measurements) 2-2 Downwelling irradiance in the Bay of Biscay 17 2-3 Temperature profile for Bay of Biscay 17 Station 2-4 Spectral effects of chlorophyll pigments 19 Effect of chlorophyll concentration on color 21 of downwelling irradiance x LIST OF FIGURES (continued) Figure Title 2-6 Photosynthesis vs light intensity for 24 three classes of phytoplankton. 2-7 Stratification of chlorophyll as reported 26 by Strickland (1968) La Jolla, California (summer) . 2-8 Euphotic depth (1 percent of surface 27 irradiance) as a function of wavelength. 2-9 Relationship between beam attenuation 33 per meter, wavelength of maximum light transmission and apparent water color. 2-10 Comparison between optical effects of 36 water and optical effects of suspended material. 2-11 Spectra of backscattered light measured 38 from an aircraft at an altitude of 305 meters (varying chlorophyll concentration). 2-12 Scattering efficiency vs particle diameter 40 for four values of refractive index, n 2-13 Extinction efficiency (Kext ) and absorp­ 45 tion efficiency (K~bs) for three values of complex refractlve index, m = n + in' xi LIST OF FIGURES (continued) Figure Title < < 2-14 Particle size distribution (A) and 47 relative particle scattering (B) for an ocean water sample from Saanich Inlet taken in June 1966 2-15 Contrasting ocean particle size 49 distributions 3-1 Transmissometer spectral responses 55 3-2 Spectral response of irradiance meter 57 filters 4-1 Data station locations 65 4-2 Downwelling and upwelling irradiance 68 profiles (Station 1) 4-3 Temperature, transmissibility and 69 particulate volume profiles (Station 1) 4-4 Downwelling and upwelling irradiance 71 profiles (Station 2) 4-5 Temperature, transmissibility and 72 particulate volume profiles (Station 2) 4-6 Downwelling and upwelling irradiance 74 profiles (Station 3 ) 4-7 Temperature~ transmissibility and 75 particulate volume profiles (Station 3 ) xii LIST OF FIGURES (continued) Figure 4-8 Downwelling and upwelling irradiance 77 profiles (Station 4) 4-9 Temperature, transmissibility and 78 particulate volume profiles (Station 4) 4-10 Downwelling and upwelling irradiance 80 profiles (Station 5) 4-11 Temperature, transmissibility and 81 particulate volume profiles (Station 5) 4-12 Downwelling and upwelling irradiance 83 profiles (Station 6) 4-13 Temperature, transmissibility and 84 particulate volume profiles (Station 6) 4-14 Depth at which the downwelling 87 irradiance was one percent of surface values 4-15 Diffuse attenuance and equivalent 89 euphotic zone depths vs particle concentration 4-16 Ratio between upwelling and downwelling 92 irradiance measured just below the water surface 4-17 Beam attenuation profiles for polluted 93 and natural water stations 4-18 Downwelling and upwelling irradiance as 97 a function of optical depth xiii LIST OF FIGURES (continued) Figure Title 4-19 Particle size distributions--environ­ mental range 100 4-20 Particle size distributions by volume, 102 V: environmental range for polluted and natural waters 4-21 Particle size
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