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plankton, marine spermatophytes, and benthic microflora are about 
equally important as primary producers. He found that the compensa- 
tion depth for phytoplankton is 5 to 7 meters, but the critical depth 
(of Sverdrup) is never less than 25 meters, and is typically much 
deeper. He concludes that the entire bay is productive throughout the 
year, with the greatest production between 1 and 7 meters depth. 
THE ROLES OF SEDIMENT IN THE WET LANDS 
The sedimentary nature of the estuaries is dependent upon complex 
interactions between the physiography and geology of the estuary and 
the watershed draining into the estuary, the circulation of the estuarine 
waters, climatic factors, and biological processes. Good detailed dis- 
cussions of the sedimentary regime can be found in Lauff.! This paper 
will consider the sediments themselves only in so far as they affect 
productivity. 
Sediment in the estuary may be suspended in the water or deposited 
on the bottom, and in either case it affects primary production. In 
addition, the active processes of sedimentation, such as erosion, de- 
position, and transportation also affect energy flow. To some extent, 
this discussion must also consider the processes taking place in the local 
environment of suspended particles, in so far as these affect produc- 
tivity. 
It seems obvious that if a large concentration of sediment particles 
(for example clay and organic detritus) is suspended in the water, then 
penetration of light will be sharply reduced. There have been numerous 
studies of the effect of suspensoids in scattering and absorbing light, 
but these results are somewhat superfluous to this paper. More to the 
point are studies which relate light penetration directly to the con- 
centration of suspended particles. A good example of this type of study 
is by Chandler,? who determined turbidity (the inverse of trans- 
parency), temperature, standing crop of phytoplankton, and quantity 
of suspended matter, both organic and inorganic, at depths from the 
surface to 10 meters over the period of a year. He found that light 
penetration varied by a factor of 10 depending on the concentration 
of suspensoids: the depths to which 1 percent of the light penetrated 
varied from 9.7 to 0.8 meters; the percentage of light reaching a 
depth of 1 meter varied by a factor of 10.8, and the maximum light 
reaching 2 meters depth was 86.6 times greater than the minimum. 
Chandler showed that these differences are caused by variations in 
turbidity, which when expressed in terms of suspended sediment 
varied from 5 to 230 parts per million, and not to changes im the 
nature of incident light. Fluctuations in turbidity took place sea- 
sonally, the water being most transparent in winter, spring, and early 
summer, and least. transparent during late summer and autumn. 
Further changes in turbidity took place weekly or daily due to changes 
in meteorological conditions. In areas where tidal currents are ex- 
ceptionally strong, such as the Bristol Channel and Severn Estuary,° 
turbidity may vary much more markedly, by a factor of 30, for 
example, between daily samples. 
Such variations in,the turbidity can be expected to have important 
effects upon photosynthesis. Pomeroy * has shown that production 
by the marine spermatophyte Thalasia showed a linear relation to 
the intensity of radiation reaching the plants. The restriction of 
‘Footnotes at end of article. 
