based upon available knowledge is that turbidity and sediment effects on marine organisms 

 from offshore dredging of sand and gravels are to be considered generally insignificant or 

 short-term. 



Peculiar local bottom -current effects on sediment transport should be monitored on 

 individual projects. 



c. Miscellaneous Effects and Considerations. A prime concern of many authorities, 

 (for example, Loosanoff, 1962, p. 13, Thorson, 1964, p. 99, and Wilson, 1958) is the 

 effect of change in water clarity (effect of suspended solids) and the effects of bottom 

 deposits on larval development and particularly larval settlement. Larvae of 

 bottom-dwelling invertebrates have subtle requirements that must be met before the larval 

 stages will leave the water column, settle to the bottom and transform into juveniles. The 

 nature of dissolved organics in bottom deposits and other unknown conditioning factors 

 influence the settling of larvae. Conclusive evidence for or against dredging effects on larval 

 stages is not avadable. Periods of greatest larval incidences in the water column of those 

 species important in the bottom communities should be observed. Ideally, dredging periods 

 should be adjusted to allow settlement to take place with least interference. 



Other factors of concern are effects of seabed topographic changes created by dredging, 

 and other effects due to deepening areas. Both effects can be mitigated by shallow 

 stripping operations when desirable. Manmade refuges through creation of deepened areas 

 provide habitats for fish. 



d. Dredge Operation— Monitoring and Management. Although no strong basis for 

 disapproval of dredging for sands and gravels in offshore areas has been found, steps should 

 be taken to include safeguards in dredging to ensure environmental quality or to meet 

 other special conditions. 



Proper environmental dredging management should include precautions to control 

 adverse sediment effects by taking advantage of tidal currents and littoral currents to guide 

 sediments put in suspension by dredging. Use of currents to control direction of suspended 

 sediment flow could improve the environment through deposition of the sediments 

 selectively and through directed dispersal of released nutrients. 



Where green plants are present, water clarity during daylight hours is important for 

 maintenance of primary productivity, and dredging only at night may be necessary. 

 Conversely, studies of faunal day-night activity may show that dredging at night may harm 

 the animal community, and dredging may have to be restricted to daytime hours. This 

 emphasizes the need for many local studies. 



Other controls could increase benefits by retention of an agreed percentage of the sand 

 substrate, bypassing concentrations of valuable living resources, and otherwise planning 

 dredging for ecosystem protection and enhancement, with the least cost and least harm. 



Monitoring can be a positive rathern than a negative adjunct to dredge operations. As a 

 part of dredging management, monitoring can supply on-site information to aid future 

 management decisions. In a sequence of research involving before, during, and after 



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