was minimized by rigorous training of the field crew prior to initiation of ttie sampling season and QC audits 

 of the field crew that were performed throughout the sampling season. Although the magnitude of variability 

 in the indicator that is associated with these sources of measurement error were not quantified, field crews 

 consistently scored >95% efficiency in all field activities. We believe that measurement errors were minimal 

 due to the standardized methods employed and the thorough training and QC requirements imposed on the 

 personnel. 



As detailed in Guideline 6: Quality Assurance, quality control measures were employed in the laboratory to 

 minimize the variability in the benthic data resulting from potential human processing error. In addition to the 

 QC requirements of 10% resorts and reidentifications, QC audits were performed on the laboratory as well. 

 The results of the QC for the benthic laboratory are listed in Table 3-5. 



Guideline 9: Temporal Variability - Within the Field Season 



\t is unlikely in a monitoring program that data can be collected simultaneously from a large number of 

 sites. Instead, sampling may require several days, weeks, or months to complete, even though the data 

 are ultimately to be consolidated into a single reporting period. Thus, within-field season variability should 

 be estimated and evaluated. For some monitoring programs, indicators are applied only within a particular 

 season, time of day, or other window of opportunity when their signals are determined to be strong, stable, 

 and reliable, or when stressor influences are expected to be greatest. This optimal time frame, or index 

 period, reduces temporal variability considered irrelevant to program objectives. The use of an index 

 period should be defended and the variability within the index period should be estimated and evaluated. 



EMAP-E chose to implement sampling during the summer (July to September) because this was the period 

 during which the stressors of concern {i.e., contaminants and DO) would most severely impact the biota. 

 During the summer index period, benthic organisms are most active, temperatures are highest, hypoxia 

 occurs more frequently, and predation is at its peak. In estuaries especially, the added pressures attributed 

 to human populations (e.g. , recreational boating, fishing, increased water usage and municipal effluent, nonpoint 

 source runoff of nutrients from agricultural lands) are at their highest during the summer. It is during this index 

 period that we are most likely to detect impacts of stressors on benthic communities. 



The benthic index was computed for all sites sampled by EMAP-E in the Louisianian Province from 1991 to 

 1 994. Because the index was developed from a subset of sites sampled in 1 991 and 1 992, validation of the 

 benthic index was accomplished by using an independent set of data from two subsequent years, 1993 and 

 1 994, as well as data from special study sites representing between-year and within-year replicates. Validation 

 of the benthic index consisted of three steps: assessment of the correct classification by the index of an 

 independent set of degraded and undegraded sites, comparison of the cumulative distribution function of the 

 index among four years, and correct classification of replicate sites by the index. 



Within each year (excluding 1 991 ), 1 3 estuaries were visited more than once in order to evaluate spatial and 

 temporal replication. These sites were used to validate the consistency of classification of the benthic index. 

 The same classification by the benthic index should be given to a single site on replicate visits within a 

 sampling season. The distribution of benthic index values between the first and second visits to a site within 

 the same sampling period was compared (Fig. 3-4). The shaded areas indicate the marginal zone between 

 the threshold values of 3.0 for degraded sites and 5.0 for undegraded sites. Ideally, all of the points should fall 

 in quadrants 2 and 4 where sites were classified as degraded on both visits or as undegraded on both visits. 

 However, although several points fall within the lightly shaded area, indicating that the site classification 



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