Objective assessment of the effects of increased concentrations of suspended sediment caused by human activities, such as navigation dredging, on estuarine fish and shellfish requires an integration of findings from biological and engineering studies. Knowledge is needed of (1) the suspended sediment characteristics typical of both ambient and dredging-induced conditions, (2) the biological responses of aquatic organisms to these suspended sediment dosages, and (3) the likelihood that organisms of interest will encounter suspended sediment plumes. This paper synthesizes the results of studies that report biological responses to known suspended sediment concentrations and exposure durations and relates these findings to suspended sediment conditions associated with dredging projects. Biological responses of taxonomic groups and life history stages are graphed as a function of concentration and exposure duration. The quality and taxonomic breadth of studies on which resource managers must rely when...

Biological Effects of Suspended Sediments: A Review of Suspended Sediment Impacts on Fish and Shellfish with Relation to Dredging Activities in Estuaries

Sediments supplied to an estuary undergo repeated cycles of resuspension and deposition prior to permanent accumulation or transport into the sea. A review of published literature and field observations of estuarine suspended sediment in the Chesapeake Bay region, indicate that sediment is resuspended in response to fluctuating energy over a wide range of time scales. The temporal variations of resuspension, therefore, inherit a hierarchy of scales following the scales of motion.

Effects of Fine Sediment Resuspension in Estuaries

Hopper dredging operations release suspended sediment into the environment by agitation of the bed and by discharge of overflow slurries. Monitoring of turbidity and suspended sediment concentrations in central Chesapeake Bay revealed two plumes: (1) an upper plume produced by overflow discharge and (2) a near-bottom plume produced by draghead agitation and rapid settling from the upper plume. The upper plume dispersed over 5.7 km2 extending 5,200 meters form the discharge point. Redeposited sediment accumulated on channel flanks covering an area of 6.4 km2 and reached a thickness of 19 cm. Altogether dredging redistributed into the environment an estimated 100,000 tons of sediment or 12 percent of the total material removed.

Effects of hopper dredging and sediment dispersion, chesapeake bay

Two series of laboratory experiments mimicking dredging of the uppermost phosphorus (P) rich sediment layers of the shallow eutrophic L. Muggelsee were carried out to study the extent of P release from deeper sediment layers, and changes in P mobility by means of fractional P composition of the in 10 cm steps ‘dredged’ sediment cores. In the first run over 38 days, the aerated controls reached 55%, and the ‘dredged’ cores from 18.1% (−10 cm) down-core to 0.4% (−50 cm) of the non-aerated control (50.82 mg P m−2 d−1 = 100%). In the second run over one year, the fractional P composition in the revealed sediment layers changed slightly. The water-soluble P (H2O-P) increased for the respective ‘dredged’ horizon by between 1.5 and 5.6% TP. The redox-sensitive P (BD-P) increased in each horizon from the intact core to the situation following ‘dredging’, as well as with depth in each horizon from 4.9% TP (−10 cm) to 11.4% TP (−40 cm). The organic bound P portion (NaOH-NRP) decreased least (1.7% TP) in the uppermost layer and most (15.6% TP) in the deepest horizon exposed to water after ‘dredging’. Based on the changes in P pools following dredging at the future sediment–water interface, it is predictable that dredging without reduction of the external loading may give only temporary improvement followed by a slow return to the present situation.

Assessment of the long-term effectiveness of sediment dredging to reduce benthic phosphorus release in shallow Lake Müggelsee (Germany)

Abstract : Seasonal restrictions on dredging and/or disposal operations are based upon concerns about potential dredging- or disposal-induced negative impacts to biological resources. In many cases, however, information on the degree to which either naturally occurring or dredging-induced environmental alterations directly or indirectly affect organisms is poorly quantified, in which case restrictions are based upon a reason to believe notion. This report addresses the general acceptability of seasonal restrictions through a compilation of available information on physical-chemical environmental alterations associated with dredging and disposal operations, and critical information regarding the effects of these alterations on principal biological resources. Based on this information, a method for evaluating existing or proposed seasonal restrictions on dredging and/or disposal operations is presented. This framework reflects the present understanding of effects of dredging- or disposal-induced, as well as naturally occurring, environmental alterations upon biological resources. In many cases, the magnitude of dredging- or disposal-induced alterations falls well within the range of naturally occurring phenomena and imposes little or no additional stress upon resource populations. In some cases, however, the magnitude of alterations may exceed that which occurs naturally, whereby concerns about dredging- or disposal- induced alterations are justified and should be considered when planning a project.

/pdf/a-framework-for-assessing-the-need-for-seasonal-restrictions-48vsh8e4d9.pdf

A framework for assessing the need for seasonal restrictions on dredging and disposal operations

Sediment-Water Interaction during Dredging Operations

: The report presents the results of a five year, interdisciplinary study of the impacts associated with dredging operations with open water disposal in San Francisco Bay and the ocean and evaluates alternative disposal methods including land disposal and marsh development. (Author)

Dredge Disposal Study. San Francisco Bay and Estuary. Main Report.

During dredging and disposal operations, there is an increase in the suspended solids in the area of activity. These resuspended sediments can adverse impact biota. The suspended solids concentrations during various dredging and disposal operations in San Francisco Bay were monitored. The results of this monitoring were integrated with the results of a suspended solids test performed at the Bodega Marine Laboratory to develop a matrix of potential adverse effects on indigenous organisms under various suspended solids loadings. The matrix indicates that under winter condition of low temperature and high dissolved oxygen adults of most species should not be adversely influenced during periods of either dredging or disposal. However, during summer months, if temperature increases to above 18\deg C and dissolved oxygen drops below two parts per million mortality of sensitive species in the lower water column may result during disposal operations. The field investigations indicated that dredging could create a fluff zone at the sediment-water interface which because of its persistence might have adverse influence on benthic organisms.

Effects of suspended solids associated with dredging operations on estuarine organisms

Studies were conducted on San Francisco Bar in June 1971 and February 1972 to monitor dredge material disposal. The purpose of the study was to determine the effects of dredging and material disposal on the physical and biological environment and to develop dredging procedures and disposal sites to mitigate possible adverse effects.. This paper presents the results of the material dispersion portion of the study including bottom deposition, current measurements and aerial photography. The biological studies and water quality monitoring are not presented.

/pdf/san-francisco-bar-dredge-material-disposal-1rncrw4d2v.pdf

John F. Sustar

Papers

Sediment-Water Interaction during Dredging Operations

Dredge Disposal Study. San Francisco Bay and Estuary. Main Report.

Effects of suspended solids associated with dredging operations on estuarine organisms

San francisco bar dredge material disposal