A conditional probability approach also will be explored to determine possible effects of 
suspended sediments on the biotic condition of streams. Data from the ORD/EMAP Mid- 
Atlantic Highlands Assessment (MAHA) streams program (EMAP indicators and design), 
reported in the MAHA streams report (EPA 2000), will be used in this application. The 
approach uses survey data (sites selected with a probability design) and determines the likelihood 
of impaired biological conditions for varying threshold levels of exposure or stressor variable(s) 
(in this case, some form of suspended sediment concentration, possibly normalized for an 
expectation level). The use of survey data permits an unbiased extrapolation of results to the 
statistical population that the probability sample was drawn from. For example, the results 
would be applicable to all of the wadeable streams in a state if the sample was drawn from all 
wadeable streams in the state. 
This approach is different from typical association approaches that relate exposure or stressor 
conditions with impaired biological conditions, for example, water quality levels associated with 
impaired fish communities (fish IBI values less than 3). The approach here “stratifies” the 
resource for exceedance of a specified exposure or stressor value and then determines the fraction 
of that strata with impaired biological conditions. Since the sites were selected with a probability 
design, the fraction of the resource that is impaired is the probability of observing impaired 
biological conditions in the resource for exceedance of the threshold value. This stratification is 
then done for all values of the exposure or stressor variable. The result is a relationship for 
probability of impaired biological conditions for exceedance of the exposure or stressor values. 
This result is not a cumulative distribution function of the biological conditions since it relates 
the conditions to a threshold level of another variable, and it is more than a simple scatter 
diagram of biological condition with the exposure or stressor variable (the resource is 
incrementally integrated or summed for second variable). 
Issues associated with suspended and bedded sediments may be approached in a slightly different 
manner in estuaries. One of the primary research needs is to determine whether sea grass decline 
is correlated with the presence of increased suspended sediments. A combination of laboratory 
and field work derived under natural (box lb) and controlled conditions (box Ic) is needed to 
derive protective water clarity criteria or to set management goals to maintain existing sea grass 
coverage and community composition. This would be accomplished by the collection of 
descriptive data (mapping and field data) at a variety of sampling sites. This research would 
include monitoring basic characteristics of sea grass communities in reference areas and areas 
which historically receive high levels of suspended solids using fixed transects or experimental 
plots. Response parameters would include, but not be limited to, photosynthetic activity, 
standing crop, root/shoot ratios, epiphytic coverage, blade characteristics, sea grass cover, and 
density. Extensive water and sediment quality monitoring would be combined with this effort. 
There are a variety of experimental designs available to determine, under controlled conditions, 
the effects of suspended and bedded sediments on sea grass and other important submerged 
aquatic vegetation. The determination of sensitive species, sensitive response parameters, and 
modifying environmental factors are the objectives of these studies. The experimental designs 
include exposing different species in laboratory tests to different levels and types of suspended 
solids alone and in combination with other factors (such as salinity and nutrients) to determine 
effects on light reduction and accompanying effects on biomass, pigment content, and other 
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