Sediment sampling

Written by Dana Davis

On September 29, 2009, our class went into the marsh at low tide behind Savannah State University's marine science building and collected sediment samples. Push corers were used to collect sediment from 5 different sites. The push corers used were clear, hard plastic tubes that opened on each end, similar to a paper towel roll. By pressing the push corer straight into the ground until sediments reached a marked line of 10 cm, the sediments were collected with little disturbance of the environment. The sample sites began at the outer edge of the marsh and continued towards the creek at intervals of about 3-5 m apart. Next, the sediment samples were taken back to the lab to be sieved and weighed. A sieve consists of several plates with different sizes of mesh in between in order to separate the different sized sediment particles. For each sample, the sediment was placed on the top of a sieve beginning with 500 micrometers, then 250, 125, and ending with 63 micrometers. Tap water was used to help transfer the sediment through to each plate. This was a time-consuming task, and 4 of the 5 samples were separated out. Next, the sediments were placed into the dryer on pre-measured tins for 24-48 hrs. The sediments were then re-measured when completely dry.

The 500 micrometer sieve was not included in further calculations due to the large amounts of plant matter, debris, and rocks in all samples. The largest percent of sediment for all 4 samples was deposited in the 125 micrometer sieve consisting of fine sand. For sites 1 and 3, the samples collected farthest from the creek, the majority of sediment was composed of fine sand particles followed by medium sand particles. Sites 4 and 5 were collected closer to the creek and were comprised of mostly fine sand particles with very fine sand being the next abundant sediment.

The picture above shows a sediment sample after sieving and drying. The top left is the 500 micrometer collection then going clockwise to the 250, 125, and 63 micrometer samples.

The figure above shows the percentage of different sized sediments (250, 125, and 63 micrometers) for each site.