Field Sampling Methods 



A 1/25 m^, stainless steel, Young-modified Van Veen Grab sampler was used to collect 3 replicate sediment 

 grabs for enumeration of benthic invertebrate community composition. This grab sampled an area of 413 

 cm^ with a maximum depth of penetration in the sediment of 10 cm. Each acceptable benthic grab sample 

 was rinsed into a plastic dishpan for transport to the sieving station for immediate, aboard processing. The 

 sediment from an individual grab was sieved through a 500 ^m sieve to wash away sediments and leave 

 organisms, detritus, sand and shell particles larger than 500 |am. The contents on the sieve were rinsed with 

 site water, into 500-ml wide-mouth polypropylene jar(s). The contents of each jar were preserved by the 

 addition of 100 ml of formalin:seawater (50:50) containing Rose Bengal vital stain to yield a final formalin 

 concentration of 10% by volume. 



Expected sources of error in the field sampling methods were reduced by mandatory training of all field 

 personnel in proper collection methods including determination of acceptable grabs, sieving techniques, and 

 preservation of the sample. However, slight measurement error could occur if the volume of sediment in a 

 grab was not consistent among grabs or if there was not sufficient water and formalin in the sample jars to fill 

 the jar (in order to prevent agitation of fixed organisms). Human error could occur also in the transfer of 

 samples from grab to sieve to sampling jar. These sources of measurement error were minimized by thorough 

 training of all field personnel and random quality control audits to ensure that proper sampling techniques 

 were being employed. 



The field sampling methods employed by EMAP-E are not expected to cause significant disturbance to a 

 site. The grab samples an area of 413 cm^ with a maximum penetration depth of 10 cm; this results in a 

 maximum sample volume of 4 liters. After 3 grabs were taken, whether successful or not, the anchor line 

 was let out to move the boat 5 m downstream to ensure that the exact 413 cm^ location was not sampled 

 repetitively. Because EMAP-E samples each station at a single point in time, the adverse effects of disturbance 

 at any site are minimal. There are no species of estuarine benthic macroinvertebrates currently listed as 

 endangered, threatened, or protected in the Gulf of Mexico. Although most sampling occurred in open-bay 

 bottom, occasionally a site was located in a protected submerged aquatic vegetation (SAV) habitat, in which 

 case, special care was taken not to unduly disturb SAV. 



Laboratory Processing Methods 



The samples were shipped directly from the field to the laboratory where they were again washed through 

 500 [im mesh sieves. Benthic fauna were sorted from the sediments, identified to lowest practical taxa, and 

 enumerated. Only benthic macroinvertebrates were identified. Meiofauna and taxonomic groups having 

 only planktonic forms were excluded from the identification process. At least one qualified benthic taxonomist 

 was required in order to provide authority on identification of taxa. 



Expected sources of error in laboratory processing included errors in handling of samples, inefficient sorting 

 and inaccurate identifications. These sources of error were minimized by rigorous quality control measures 

 that included random resorts and recounts and by having qualified and trained personnel performing the 

 sorting and identification of taxa. 



Data Manipulation Methods 



The benthic macrofaunal count data were sent to a data manager in dBase® format. The data manager 

 translated this data into SAS® format. The data was then checked for transcription errors, and inconsistencies 

 in taxonomic coding as well as new taxonomic codes. Detailed methods for the development and application 

 of the benthic index are found elsewhere (Engle et al. 1 994, Engle and Summers 1 998, Engle and Summers 

 1999). The benthic parameters that make up the components of the benthic index were calculated for each 

 sampling station (Table 3-1). The benthic index was calculated by combining the components in a linear 

 fashion as illustrated in Table 3-2. 



3-8 



