SUBTIDAL RESULTS 

 Sedimentary Environment 



Quarterly mean grain size and silt/clay content of subtidal sediments from June 1979 to March 

 1986 are plotted in Figure 8. Sediments at subtidal stations ranged from fme to coarse sands and 

 contained up to 40% silt/clay. Bottom sediments at IN were composed of fine (0.125-0.25 mm) to 

 medium (0.26-0.50 mm) sands. Since December 1983, seven of ten quarterly values were lower than 

 those obtained prior to this period. At EF, sediments were composed of fine to medium sand. Coarse 

 sands only predominated in March 1981. Grain size at this station was relatively stable at this station 

 until .lune 1985; since then greater seasonal variations and a general increase in mean grain size have 

 occurred. Sediments at GN were generally composed of medium sands, although over the sampling 

 period they ranged from 0.14-0.76 mm. From March 1979 to March 1983, grain size at this station 

 gradually increased and since then, relatively larger seasonal peaks in grain size have been evident during 

 September. Sediments at JC were mostly medium sands, although coarse sands sometimes occurred 

 during winter months (i.e., December and March). Of all stations, JC sediments were among the 

 coarsest during the study. 



Silt/clay content of subtidal sediments ranged from 1.3 to 44.1%. At GN, silt/clay ranged between 

 10% and 20% and has been relatively consistent since December 1980. At IN, silt/clay ranged from 

 5.5 to 44%, although 17 of the 28 values were between 5% and 10%. Since June 1983, IN sUt/clay 

 content increased to levels higher than those previously observed. Silt/clay values at JC ranged from 3 

 to 24%; however, 23 of 28 values were less than 10%. At EF, silt-clay content ranged from 2-14%, 

 and 26 of 28 values were between 1% and 10%. 



Sedimentary characteristics of all stations, except JC, have exhibited some temporal shifts during 

 the study. Values for grain size at Giants Neck grain size have generally increased since 1982. This 

 trend is believed attributable to the increased amounts of Mytilus edulis shell found in the sediments. 

 This shell increases the overall weight of sediment retained by larger sieves during analysis and inflates 

 grain size values. At IN, higher and more variable silt/clay values have been observed since June 1983, 

 when construction activities (dredging and coffer dam removal) resulted in the deposition of fine material 



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