Provide the scientific basis for suspended and bedded sediment criteria for marine and freshwater 
systems. 
Critical Path 
A general diagram for NHEERL’s research program on suspended and bedded sediments is 
shown in Figure 7. An explanation of the figure is given below, including the logical sequence 
of information needed to develop the technical basis for deriving a criterion for suspended and 
bedded sediments. 
The major NHEERL responsibilities in Figure 7, under Goal 2, are to: review the literature and 
existing State criteria and develop a general conceptual model of sediment effects, including 
verbal descriptions of suspended and bedded sediment criteria that are explicit enough to shape 
subsequent quantitative modeling (box 0). Based on regional-scale data (box la,b), develop 
ecoregionally-specific models of the effects of suspended and bedded sediments on aquatic 
assemblages in various types of aquatic ecosystems (box 2); then explore and confirm 
mechanisms of sediment effects on assemblages and ecosystems through experimental research 
incorporating controlled conditions and restricted taxa at smaller scales (box Ic). Using these 
stressor-response relationships and models as a technical basis, develop an approach for 
establishing sediment criteria (box 3), which OW, EPA Regions, and States may use to establish 
criteria for suspended and bedded sediment (box 5). Using data from regional-scale surveys 
(e.g., EMAP, Regional EMAP [REMAP], National Water Quality Assessment [NAWQA)]) and 
more focused watershed studies, examine the stressor-response relationships between natural and 
anthropogenic controls and the levels and transport of sediment (box 8). Based on this research 
and models of the effects of sediments on aquatic biota (box 2), identify critical thresholds of 
anthropogenic disturbance that lead to biologically-relevant sediment responses (box 4). These 
ecoregionally-specific thresholds will be useful guidance to the TMDL process carried on by 
States (box 6). Finally, review and revise the stressor-response models and recommended 
sediment criteria based on feedback from monitoring data and further research (box 7). 
The first step in this process is a review of the literature on the biological effects of suspended 
and bedded sediments. The Office of Water has already begun this process. NHEERL can 
contribute to this effort and expand it to evaluate the literature for useable stressor/response 
relationships. Once the available literature has been reviewed, it will be necessary to develop a 
conceptual model or framework of the effects of suspended and bedded sediments in aquatic 
environments (box 0). This will guide the development of the remainder of our research 
activities. 
Classification of the expected response of aquatic systems to suspended solids and bedded 
sediments is a critical early phase of research. The first step in developing a classification 
scheme for sediments and suspended solids is the division of the national landscape into different 
eco-regions that are sufficiently fine-scaled to accurately represent the vegetation, climate, 
geology, and soils (box la). These factors will influence both the quantity and type of sediment 
and suspended solids that will be carried from the landscape into the receiving water body. The 
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