We will use the following procedures to help determine the health of a site. These processes involve capturing falling sediments and taking bottom samples from lakes and ponds.
- Bottom Grab
- Sediment Trap Designs
- Determining Organic Carbon based upon Loss on Ignition
How to do a Bottom Grab
A bottom grab is collected by lowering a device to collect a sample from the floor of the ocean or a lake.
- Fish Finder
- Bottom Grab
- Large open-mouth bin
- Smaller containers (e.g. Ziploc bags)
Image courtesy of University of Vermont Environmental Sampling and Monitoring Primer
- Open the bottom grab.
- Set the catches on the bottom grab to hold the bottom grab open.
- From your readings on the fish finder, determine the depth.
- Lower grab into the water and allow to slam into the bottom. This will close the trap.
- Raise the bottom grab.
- Place the sediments in a large open mouth bin. As you release the grab, take samples from this container and place them into smaller labeled containers and return with them to the lab. The labels should have location, depth and your initials on them.
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Sediment Trap Designs and Considerations
Below you will find several links that will be helpful to the construction of your sediment traps. Some of these are technical articles, where the schematics will be more helpful than the text. Others you will need to consider the text carefully as they examine the efficiency and effectiveness of different designs of sediment traps. Many of the traps in the following pages are large ocean-going traps that out in the sea for months or years. The traps you will be designing will be significantly smaller, however elements of the designs of these large traps may be incorporated into your trap design. For a size comparison, your traps will be out for two weeks and will need to be transportable by a small boat and liftable by hand.
A New Zealand site, this page offers careful consideration of the efficiency of the trap. http://www.asrltd.co.nz/trapcalib.pdf
A German site with a good explanation of how the trap works and good pictures. http://www.ugt-online.de/english/197000.htm
From the US Geologic Survey, these sites have good illustrations and diagrams of different sediment traps. http://climchange.cr.usgs.gov/info/lacs/sedtraps.htm
From the University of South Carolina, this page features a large scale ocean going sediment trap.http://www.geol.sc.edu/msrl/sediment_trap1.htm
This Japanese site has an interesting design on it. The text is not particularly useful however. http://www.nirs.go.jp/ENG/nakami2.htm
Another page featuring large oceangoing traps, this site offers a variety of design ideas. http://www.d.umn.edu/llo/Vessels/photo.html
Again large ocean traps, but lots of pictures and good design ideas. http://strata.ocean.washington.edu/STRATAFORM/field.html
More good pictures and design ideas this time from the Navy. http://www.oc.nps.navy.mil/~icon/photos/cruise_photos.html
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Carbon Analysis in a Mud Sample Based on Loss on Ignition
This process describes how to find the carbon content in a samples of mud. The samples for these experiment will come from a bottom grabs. This is the laboratory process for analyzing the bottom grabs.
- Evaporation dish
- Wax pen
- Mud samples
- Oven gloves
- Muffle Furnace
- Drying Oven
- Take your evaporation dish, make sure it is dry, and label it with the site and sample number with the wax pen. Write clearly so that if the wax begins to melt, it will remain visible.
- Weigh and record weight of evaporation dish.
- Place approximately 5 grams or 2 Tbsp of mud into the evaporation dish.
- Put on gloves, and using the tongs, place in the drying oven. The drying oven will dry at a temperature of about 105° Centigrade.
- Leave the samples in the drying oven for at least 24 hours to ensure that all of the water is out of the sample.
Doing Loss on Ignition
- Take your sample out of the drying oven. Be careful as the dishes will be hot. Use tongs and gloves.
- If you cannot use the muffle furnace right away, allow to cool in the hood and then place in the desiccator. It must be cooled some or else you will melt the desiccator. However, do not leave out for too long or the mud will begin reabsorbing moisture.
- Preheat muffle furnace to 550° Centigrade. This will take 15-30 minutes.
- Place the crucible into the muffle furnace, draw a map of where each sample is so that if the wax does melt you will not lose the sample and site numbers.
- Burn samples for exactly one hour.
- The muffle furnace will heat the mud to over 550° Centigrade, which burns off the organic carbon.
- Take the crucibles out and allow to cool under the hood. Use gloves and tongs, as the crucibles will be extremely hot.
- After the samples are cooled, weigh them again.
- Use the following equations to find the percentage of carbon.
[ Mdry weight - Mcrucible]-[Mburned weight-Mcrucible] = Morganic carbon
[Morganic carbon/(Mdry weight-Mcrucible)]x 100 = Percent Carbon
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Materials List for Benthic Sampling
- ___Sediment Trap(s)
- ___Bottom Grab
- ___Fish Finder
- ___Large open-mouth bin
- ___Smaller containers (e.g. Ziploc bags)
Loss on Ignition
- ___Evaporation dish
- ___Wax Pen
- ___Mud Sample
- ___Oven Gloves
- ___Muffle Furnace
- ___Drying Oven
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