micrometers Si02 for the other two species (Figs. 7 and 8) . _ The carbon 

 uptake curves for M. lutheri^ Chlorella sp., and Nannochlovis sp. were 

 practically the same shape (Fig. 8) and were not linear. The peculiar 

 shape of the Stichocoaous sp. curve (Fig. 8) supports the idea that 

 photosynthesis for this species was light-limited even before exposure 

 to concentrations of solids. 



These changes in carbon uptake support the relationships reported 

 by Biggs (1970) for increasing suspended particle concentration and 

 decreasing transmission of light in water determined with increasing 

 concentrations of kaolinite (median size = 4.0 micrometers). The 

 kaolinite concentrations decreased the light less than the same concen- 

 trations of particles occurring in a natural water sample (median size 

 = 1.9 micrometers). 



The effects of Si02 on M. lutheri were less than for either 

 Nannoohloris sp. or Chlorella sp. (Figs. 5, 6, and 7). However, M. 

 lutheri was exposed to a median particle size of 17 micrometers, as 

 opposed to 6.2 micrometers for the other two species. Evidently, 

 greater carbon uptake by M. lutheri was partly due to increased light 

 transmission through the larger particles, although concentrations were 

 identical for all species. A concentration of 2,250 milligrams 1"^ Si02 

 caused an 80-percent reduction in carbon uptake by M. lutheri. At 1,000 

 milligrams l"l this reduction was approximateTy 50 percent. For the 

 other three test species in the finer SiOg, at 1,000 milligrams 1"^, the 

 the reduction was almost 90 percent. 



The motility of M. lutheri must also be considered. As light inten- 

 sity attenuated, this species could have moved toward the sides of the 

 incubation bottles, i.e., nearer to the source of incident light. This 

 movement might have contributed substantially to improved carbon uptake, 

 although it was still much reduced at higher concentrations of Si02. 



Regardless of particle-size distribution relationships, the reduc- 

 tions in carbon uptake demonstrated for concentrations between 100 and 

 500 milligrams l-i are biologically significant with respect to the 

 reduced energy available to filter-feeding organisms (see Section II). 

 Concentrations of particles with similar size distributions are typical 

 of those occurring during dredging and disposal operations (May, 1973; 

 Masch and Espey, 1967) (see Table A-3, App.), resuspensions during 

 storms, or as normal "high" background values in Galveston Bay (Masch 

 and Espey, 1967) and Louisiana marshes (Mackin, 1961) . 



An additional factor associated with dredging may be the release of 

 organic matter and minerals into the water column which may be either 

 beneficial and stimulate growth (Odum, 1973; Flemer, 1970) or detri- 

 mental. The amount T)f material released (May, 1973) and the dilution 

 rate is unknown. Nutrients, heavy metals, and pesticides can be 

 released into biological pathways and be magnified in the trophic 



15 



