Subtidal Results 



Sedimentary Environment 



Sediments at subtidal stations from September 

 1985 - June 1987 were comprised of very fme to 

 coarse sands which ranged in size from 0.07 - 0.55 

 mm ana contained from < 1 - 44% silt/clay (Fig. 

 9). During this period, sediments were generally 

 coarsest at EF, where medium sands (0.31 - 0.50 

 mm in size) of low silt/clay (0.7%- 5. 17%) content 

 predominated. At tliis station, there was a trend 

 for increasing grain size and decreased sUt/clay 

 content beginning in September 1985 and contin- 

 uing through .lune 1987. 



Grain size at GN ranged from 0.21 - 0.55 mm 

 and although fme-to-medium sands predominated 

 at this station, coarse sediments were obtained in 

 September 1985. The seasonal trend of coarse 

 sediments during September also occurred in 1983 

 and 1984, but not during 1986 or 1987. SiU/clay 

 at this station ranged from 10 to 20% with no 

 consistent seasonal periodicity. During 1986-87, 

 grain size and silt/clay content at this station were 

 consistent with past results (NUSCO 1987). 



Sediments at IN ranged from 0.07 - 0.21 mm 

 (very fme - fme samd) since September 1985, and 

 were within the range of those collected in previous 

 years (NUSCO 1987). Silt/clay content at this 

 station remained high, relative to other stations, 

 and ranged from 5.8 - 44.5%. Higher and more 

 variable values were obtained during 1986 than 

 in 1987. 



Temporal fluctuations in sedimentary character- 

 istics also occurred at JC during the 1986 - 1987 

 sampling period. Quarterly mean grain size ranged 

 from 0.10 mm - 0.52 mm (very fme to coarse 

 sands) and silt/clay from 3.9 - 38%. From Sep- 

 tember 1986 through .lune 1987, values for grain 

 size at this station were lower than all previous 

 observations. Silt/clay values during 1986 were 

 consistent with those observed in past years 



(NUSCO 1987). During 1987 sampling, levels of 

 silt/clay within JC sediments generally exceeded 

 those obtained in previous years. 



During the operational period, changes in sed- 

 imentary characteristics at all stations, except GN, 

 were apparently related to start-up of Millstone 

 Unit 3. At EF, the increased grain size and de- 

 creased silt/clay content was attributable to scour- 

 ing produced by the 3-unit discharge. At JC. un- 

 usually high silt/clay content was detected in Sep- 

 tember 1986, although divers reported reduced 

 visibility and unusually turbid conditions at this 

 sampling station as early as June. Reduced silt/ 

 clay at IN also corresponded to power plant start- 

 up. There was no comparable shift at the GN 

 reference station, which might indicate that a nat- 

 ural event was responsible for the changes which 

 occurred at other stations. 



General Community Composition 



The general composition of subtidal communi- 

 ties sampled during 1986 - 1987 is presented in 

 Table 4. PolychaeteS were most abundant, and 

 during 1986 and 1987 accounted for 66 - 56% of 

 the total individuals collected at GN and JC, re- 

 spectively. Oligochaetes were the second most 

 abundant group at these stations in 1986. In 1987, 

 total arthropod abundance doubled at GN and 

 increased by an order of magnitude at JC. 

 Oligochaetes dominated at EF (46% and 50%) 

 followed by polychaetes (36% and 28%). The 

 large increase in arthropods observed at GN and 

 JC during 1987 was not evident at EF where total 

 numbers collected were near the lower end of the 

 range in both 1986 and 1987. Arthropods were 

 the major component of IN communities during 

 both 1986 and 1987, accounting for 54% and 

 67% of the total individuals, respectively. 

 Polychaetes were the second most abundant 

 group, followed by molluscs. 



Polychaetes were the most diverse group and 

 accounted for the majority of infaunal species 



86 



