Nitrogen, oil and grease, chemical oxygen demand, total sulfides and phosphates, 

 and benthic animal diversity and biomass. The degree of dredging was associated 

 with the degree of potential improvement in the quality of the sediments. Dredg- 

 ing to a depth of 3 meters would restore conditions for desirable benthic com- 

 munities . 



12. BENEFIELD, R.L., "Shell Dredging Sedimentations in Galveston and San An- 

 tonio Bays," Technical Series No. 19, Texas Parks and Wildlife Department, 

 Austin, Tex., 1976. 



Sedimentation on oyster reefs caused by hydraulic mudshell dredging was 

 studied at seven sites in Galveston and San Antonio Bays. Silt baskets and 

 core tubes were used to monitor rates of sedimentation. Important factors in 

 reef sedimentation were oyster reef contours, sediment composition, direction 

 of current flow, and number of shell dredges discharging sediments. Sedimenta- 

 tion was not found on a reef 0.91 to 1.22 meters above the surrounding bottom 

 during the operation of a shell dredge 91.4 meters from the reef edge. A reef 

 with a flat profile received deposits of dredged sediments when the nearest of 

 five dredges was 1798 meters away. Sediment deposits of 10.2 to 15.2 centi- 

 meters caused oyster mortalities. It was found that each dredge site contained 

 particular characteristics and that regulations requiring inflexible minimum 

 distances between dredges and reefs were not appropriate. 



13. BOEHMER, R. , et al., "Effects of Suspended Marine Sediments on Selected 

 Commercially Valuable Fish and Shellfish of Massachusetts," Froceedings of 

 the Seventh Annual Offshore Technology Conference, Vol. I, 1975, pp. 133-141, 



With various levels of suspended, fine-grained marine sediment, acute bio- 

 assays were performed on several marine fish and shellfish to determine possible 

 lethal effects of short-term exposure to levels of suspended sediments encoun- 

 tered in the dredge plume of an offshore sand and gravel mining operation. Tox- 

 icity increasing with longer term exposure was evident with coho salmon and sil- 

 verside and, to a lesser extent, with winter flounder, hake, and bay scallops. 

 Coho salmon was the most tolerant of the fish, followed by winter flounder 

 and silverside. Although initially tolerant of higher concentrations of suspend- 

 ed sediment, menhaden, yellowtail flounder, hake, and silverside were less toler- 

 ant at longer durations. This indicates that with some species the toxicity of 

 suspended fine sediment is more dependent on the length of exposure, whereas 

 with other species the toxicity is more dependent on the concentration. The 

 highest tolerance was exhibited by the adult stage of quahog, soft-shell clam, 

 and oyster. Although these three shellfish were the most tolerant, the bay 

 scallop was the most susceptible of those species tested. Bay scallop larvae 

 were more tolerant than adults. Lobsters were relatively tolerant to suspended 

 sediments, although apparently vulnerable while molting. 



14. BOUMA, A.H., "Environmental Studies Related to Shell Dredging in Gulf 

 Coast Estuaries," Proceedings of the Seventh Annual Offshore Technology 

 Conference, Vol. I, 1975, pp. 83-91. 



Although the many estuaries along the gulf coast vary significantly in 

 physical and biological aspects, the various studies on shell dredging all 

 point to the same general conclusions. The additional suspended load re- 

 sulting from dredge discharge, the oxygen budget, and the rapid salinity 

 changes is considered to be the most important environmental aspect. The 

 impact of dredging on the estuarine environmental parameters is less than 

 would be suspected. 



