Dredge and fill activities in estuaries have many environmental effects, most, although not all, of them deleterious. These effects include reduced light penetration by increased turbidity; altered tidal exchange, mixing, and circulation; reduced nutrient outflow from marshes and swamps; increased saltwater intrusion; and creation of an environment highly susceptible to recurrent low dissolved oxygen levels. Coral, oysters, and barnacles are particularly vulnerable to the effects of siltation. Both estuarine flora and fauna may be harmed by contaminants released into the water column by dredging operations. Ways to mitigate the effects of dredge and fill operations include careful pre- and post-construction environmental studies; use of bridging to create roadbeds where coastal wetlands cannot be avoided; use of a turbidity diaper and other means to control turbidity; dredging during periods of low benthic populations or during tides that would carry coarser sediments away from productive areas such as oyster reefs; and thoughtful disposal of spoil, such as locating spoil sites on the uplands with proper diking.

Estuarine dredge and fill activities: A review of impacts

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.

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

The macrobenthic fauna in the tidal freshwater James River, Virginia, USA, exhibited a high degree of resilience and limited temporal response to sediment disturbance caused by large quantities of low bulk density (> 1.3 g cm-3) fluid mud. The fluid mud was produced by hydraulic dredge deepening of a ship channel with disposal of dredged sediments onto a nearby shoal. The response of tidal freshwater communities to fluid mud was limited to mainly quantitative changes in abundance of dominant taxa (Limnodrilus spp., L. hoffmeisteri, Ilyodrilus templetoni, Corbicula fluminea, Coelotanypus scapularis) and was directly related to the thickness of fluid mud layers. Disturbance effects were short lived and for tubificids most obvious in areas with 0.3 m fluid mud, acute effects were limited to chironomids and small (< 10 mm) C. fluminea. The fauna colonizing the areas disturbed by fluid mud was the same as that inhabiting the shoal prior to disturbance. There was no indication of a successional sequence, as reported for other freshwater and marine habitats. Three weeks after the disturbance ended, all but a few insect taxa had recolonized. Changes in community structure from fluid mud disturbance were slight with total taxa best characterizing the disturbance. The insensitivity of community structure measures reflects the high resiliency of macrobenthic communities to physical stresses in tidal freshwater systems.

Response of tidal freshwater macrobenthos to sediment disturbance

Effects of dredging on filter feeder communities, with a focus on sponges: Final Report

: The U. S. Army Corps of Engineers (USACE) is faced with increasing numbers of requests to dredge shallow, unvegetated estuarine waters. Most of those proposals involve tidal waters ranging in depth from man low water (MLW) to 1.2 m (4 ft) below MLW, with projected post-dredging depths if 1.8 m (6 ft) below MLW. This technical note summarizes what is known about the ecological functions of these habitats and the potential impacts of dredging.

Pine Re

Papers

Environmental effects of dredging and spoil disposal.