apparent RPD depth. In September 1984, this station had a mean 

 apparent RPD depth of 3.2 cm. In this survey, the station had a 

 mean apparent RPD depth of 0.88 cm, most likely the result of very 

 localized erosion (this assumption is supported by the presence of 

 a thin layer of washed sand at the surface) . The mapped 

 distribution of the mean apparent RPD depth showed that the deepest 

 RPD values were located in an area extending from 4 00E southwest 

 toward stations 200S and 200SW (Figure 3-74) . 



Overall, 50% of the replicate images from the NH-74 mound 

 exhibited evidence of Stage III infauna. In September 1984, the 

 NH-74 mound exhibited a patchily distributed Stage III infauna. 

 Two stations, 200E and 200W, showed a marked decrease in 

 successional status since that survey (Figure 3-75) . This may be 

 explained by local erosion at station 200W. The sediment profile 

 images at station 200E have relict feeding structures at depth, 

 indicating that Stage III infauna were present at this station in 

 the past. All three images also showed the presence of reduced mud 

 clasts at or near the sediment-water interface; these also suggest 

 either sediment erosion or possibly megafaunal predator foraging. 

 Either of these forces could be potentially responsible for the 

 apparent loss of Stage III infauna from this station. 



The frequency distribution of Organism-Sediment Index 

 values was bimodal with peaks at the +7 and +11 class intervals 

 (Figure 3-73) . OSI values at the same two stations (200E and 200W) 

 also had decreased dramatically; station 200W had decreased from 

 +9 to +3, and station 200E had decreased from +11 to +6. As 

 described earlier, the reasons for these decreases were most likely 

 related to local erosion (due to either physical or biological 

 forces) . The patchy distribution of OSI values (Figure 3-76) 

 reflected the mosaic of Stage I and Stage III infauna present at 

 this mound. Overall, benthic conditions at the NH-74 mound had not 

 markedly changed since the 1984 survey. 



3.3.7 New Haven '83 (NH-83) 



Three previous REMOTS® surveys were conducted at this 

 disposal mound: a baseline survey in October 1983 and post-disposal 

 surveys in January 1984 and September 1984. The results of the 14 

 August 1985 survey were compared to the September 1984 survey 

 (stations 200N and 600E were not occupied in the August 1985 

 survey) . 



The major modal grain size was >4 phi (silt-clay range) 

 at all stations with subordinate modes of very fine sand (4-3 phi) . 

 The medium sand (2-1 phi) observed at station 400N in previous 

 surveys was no longer evident, probably due to both the deposition 

 of additional fine-grained sediments and the bioturbational mixing 

 of the coarse-grained material. 



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