Section 6. 
Implementation Plan for Suspended and Bedded Sediment Research 
NHEERL's effort concerning suspended and bedded sediments has been redirected since this 
section was first written. The majority of the work in this research area will now occur under 
Goal 8 (EMAP) because EMAP design techniques will be applied to develop effect thresholds 
for suspended and bedded sediments in aquatic systems. Some of these techniques are described 
generally in the Critical Path subsection of this implementation plan. However, at this time, the 
effort under aquatic stressors will only include a literature review of suspended and bedded 
sediments research. Results from this review will be combined with EMAP app’oaches to 
synthesize and evaluate the state of the science. Once the review has been completed, data gaps 
will be identified and additional research will be conducted, if warranted. 
Probleih 
The Office of Water has identified suspended and bedded sediments as one of OW’s highest and 
most immediate priorities. The priorities within aquatic systems for developing these criteria 
were identified as: rivers and streams; followed by lakes, reservoirs, ponds, and estuaries. For 
purposes of this document, suspended sediments are those sediments that exert their negative 
impact via their suspension in the water column, such as the effect of shading induced by them 
on submerged macrophytes. Bedded sediments are those sediments that have their negative 
impact when they are actually settled out and on the bottom of the water body of interest such as 
fine sediments which smother spawning beds. Research in this section does not deal with 
contaminated sediments (those containing toxic chemicals, see Section 7). 
In streams and rivers, fine inorganic sediments, especially silts and clays, affect both the habitat 
for macroinvertebrates and fish spawning, as well as fish rearing and feeding behavior. Larger 
sands and gravels can scour diatoms and cause saltation of invertebrates, whereas suspended 
sediment affects the light available for photosynthesizing plants and visual capacity of animals 
(Waters 1995). A major problem with suspended sediment in coastal wetlands, estuaries, and 
near-shore zones is the decreased light penetration which often causes aquatic macrophytes to be 
replaced with algal communities, with resulting changes in both the invertebrate and fish 
communities (Chow-Fraser 1998). Increased sedimentation also may functionally shift the fish 
community from generalist feeding and spawning guilds to more bottom-oriented, silt tolerant 
fishes (Berkman and Rabeni 1987, Muncy et al. 1979). 
Thus suspended and bedded sediments are expected to have two major avenues of effect in 
aquatic systems: 1) direct effects on biota and 2) direct effects on physical habitat, which result in 
indirect effects on biota. Some examples of direct effects on biota include suppression of 
submersed macrophytes through reduced light attenuation, changes in benthic algal communities, 
and shifts to turbidity-tolerant fish communities. Effects of suspended and bedded sediments on 
habitat structure include changes in refligia for biota (e.g., changes in macrophyte communities), 
increased fines (and embeddedness) and scouring in streams, aggradation and destabilization of 
stream channels, and filling in of wetlands and other receiving waters (Wilcock 1998, Lisle 1982, 
Dietrich et al. 1989). Increased turbidity and concomitant changes in light regime could also be 
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