136 



The result of the surface sediment winnowing process includes six characteristics in 

 REMOTS® images: shell lag, winnowed surfaces, disturbed amphipod tube mats, physical 

 boundary roughness, and sand-over-mud stratigraphy. There are three potential causes for 

 surface disturbance of tube mats: 1) predator foraging; 2) microbial decomposition 

 following the abandonment of the tubes; and 3) disturbance from either trawling or a 

 temporary increase in near-bottom turbulence or current velocity. When tubes are 

 abandoned they are much more susceptible to physical transport by currents. 



Surface sediment reworking at NLDS appears to be limited to winnowing of fines 

 accumulated during the summer in areas where shell lag armors the surface. The shell lag 

 may form in the fall and winter during periodic storms, then again be covered with tube 

 mats that bind finer sediments in the spring and summer. This seasonal response is 

 observed to be consistent between reference areas and disposal areas, and results in a 

 fluctuation between seafloor surfaces covered with muddy tubes to surfaces with clean shell 

 and fine sand. This seasonal cycle may open opportunities for settlement of recolonizing 

 benthic organisms and explain their patchy distribution at reference areas. Any deposition 

 of fresh dredged material will begin to be exposed to this cycle and will eventually acquire 

 tubes or attached organisms depending on grain size. In general, there is evidence of fall- 

 winter winnowing in many areas of NLDS and spring-summer deposition of finer 

 materials. As shown by the long-term stability of mounds at the site (see above), this cycle 

 does not appear to result in any significant net loss or gain of sediment. 



4.2.1 Evidence of Low Dissolved Oxygen 



In some years (1995, 1997), NLDS appears to have experienced a seasonal or 

 annual environmental stress or disturbance that has affected apparent reduction-oxidation 

 conditions within the sediments across some of the disposal mounds and nearby reference 

 areas. In other years (1992, 1998) there is no evidence of such disturbance. Dissolved 

 oxygen concentrations measured in August 1992 approximately 1 m above the bottom at 

 the disposal site and reference stations ranged from 7.3 mgT 1 to 7.8 mgT 1 , while surface 

 water oxygen concentrations ranged from 7.7 mgT 1 to 8.1 mgT 1 . These results are 

 comparable to results for August 5, 1992 (7.05 mgT 1 ) from the Connecticut Department of 

 Environmental Protection Hypoxia Monitoring Program (CT DEP) measured at Station M3 

 (Kaputa and Olsen 2000). Station M3 is located at the west end of Fisher's Island, 2 nmi 

 SE of NLDS in greater than 35-m water depth (water depths at NLDS range from 14 m to 

 24 m). 



The monitoring surveys conducted in early August 1992, late August 1995, early 

 September 1997 and late July 1998 all revealed the presence of widespread tube-building 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 





