because o£ the interactions of depth, the light attenuating proper- 

 ties of seawater, and the conditions of the sky. Light of wavelengths 

 greater than 6,500 angstroms or less than 4,000 angstroms may be miss- 

 ing even in moderately clear coastal waters (Jitts, et al., 1964). 

 No form of submarine light resembles the spectral distribution of un- 

 filtered sunlight or the illumination from cool white fluorescent 

 lamps. 



Light attenuation by the use of successive layers of black plastic 

 screen provides a rough geometrical decrease in intensity. One 

 screen layer approximately reduced the intensity to 59 percent of the 

 experimental incident radiation with no screen, two layers approxi- 

 mately attenuated the intensity to 40 percent, three layers to 28 

 percent, four layers to 17 percent, and eight layers to 7 percent. 



The low light intensities used in culturing the phytoplankton 

 experimentally are thought to be typical of upper to middle turbid 

 areas of Chesapeake Bay tributaries at depths greater than 0.5 meter. 

 These intensities were calculated roughly from our own water surface 

 insolation measurements with the Y.S.I, radiometer and Flemer's 

 extinction coefficients; conversion factors were according to 

 Strickland (1958). 



Under the experimental conditions, a light intensity of 1.45 x 

 10 ergs provided nearly optimal photosynthesis by M. lutheri 

 (Fig. 1). This value is approximately 41 percent of that reported 

 by Craigie (1969) for this species. Our value is approximately 14 

 percent of that reported by Jitts, et al., (1964) for optimal erowth 

 of this species at 19° Celsius, although their preconditioning 

 intensity was roughly 4.55 x 10*+ ergs cm sec~l versus 0.8 x lO"^ 

 ergs cm-2 sec^^ in our project. They also used enriched synthetic 

 seawater with a salinity of about 29 parts per thousand compared to 

 our filtered, natural Patuxent River water enriched with f/2 medium 

 (salinity 5.5 to 7.5 parts per thousand). These data show that.M, 

 lutheri can be acclimated to grow optimally under different labora- 

 tory conditions. 



The saturation curves for Chlorella sp. (Fig. 2) and Nannoohlovis 

 sp. (Fig. 3) indicate that these species were close to light satura- 

 tion also. StichoooGous sp. is farthest from the light saturation 

 plateau (Fig. 4). 



b. Effects of Suspended Solids . Carbon uptake of M. lutheri 

 (Fig. 5) progressively decreased with increasing concentrations of 

 Si02. Nearly an 80-percent reduction in uptake occurred at 2,250 

 milligrams 1~ Si02 (median size = 17 micrometers), Chlorella sp. ^ 

 (Fig. 6) showed a 90-Dercent, decrease in carbon uptake at concentra'-U<5»i4 



of 1,000 milligrams 1 ^ of <15 micrometers Si02 (median size = 6.2 

 micrometers). Practically the same magnitude of reduction in carbon 

 uptake occurred at concentrations of 1,000 milligrams l-^ of 15 



