|
Last updated:
January 15, 2013
|
Ecosystem History of South Florida Estuaries Data
Sampling Procedures and Methods
[Return to data]
Core Collection. Core collection sites are determined on the basis of examination of digital orthophotoquadrangles, aerial photos, maps, reconnaissance, and discussion with land managers. Collecting cores is essential to the purpose of this project - to reconstruct the history of the ecosystem over biologically significant periods of time (decades to centuries) and to determine what the system looked like prior to significant human alteration. The sediments, faunal and floral remains in the cores retain this record.
All cores are collected via the "piston" coring method. This provides a minimum of disruption to the sediments. The technique of obtaining the piston core varies somewhat from site to site depending on water depth and accessibility. Following are the general procedures:
- Marking the site: Specific core site is selected in advance by snorkeling before the boat or equipment is brought up to the site. The chosen site is marked with a float.
- Set up: If the water depth allows, the boat is floated up to the site, anchored on at least two sides, and coring conducted through a "moon pool" (hatched hole in the bottom or back of the boat). If water depth does not allow us to float the boat over the site, we place the coring equipment on a raft or rubber dinghy, snorkel and float to the site, and proceed with coring. A tripod may be set up and utilized to assist in extracting the core. This is especially useful if the cores are long (>1.5 m) and/or if the substrate is very firm. If used, the tripod is set up prior to starting the actual coring. The purpose of the tripod is to keep tension on the piston while the core is being pushed down into the substrate.
- Inserting the core barrels:
- The piston (a hard rubber plug with 2 O-rings) is inserted into the bottom of a 4" outside-diameter clear acrylic tube, and a rope attached to an eye-ring in the top of the piston is threaded back through the core barrel.
- The core barrel is lowered to just above the substrate and any air trapped in the space between the piston and the bottom of the barrel is removed and filled with water. Tension is then placed on the line attached to the piston, so when the core barrel penetrates the sediment the piston remains in a fixed position a few cm above the sediment surface; this produces a vacuum that retards compaction.
- When the barrel is set in position it is forced down into the sediments (via muscle power) until we hit bedrock or until we cannot push the core any further. If a replicate core is being taken (side by side cores), the second core is pushed in place at this time, before the first core is extracted so that no disruption of the sediments for the second core will occur due to sediment movement during the extraction process. An aluminum clamp device with handles is usually placed around the barrel to provide a good grip for pushing.
- Extracting the core barrels:
- If a tripod was not set up, the aluminum clamp handles are used to extract the cores via muscle power. If a tripod is used, a cable and pulley system can be used to lift the core via a hand winch. With either method, it is critical to keep tension on the piston, because the piston provides the vacuum to retain the sediments in the core barrel as it is lifted. A benefit of the clear core barrel is that it allows us to determine if the piston is moving or if any leakage around the piston's O-ring seal occurs during the extraction process.
- As soon as the core barrel clears the sediment surface, a person standing in the water quickly places a plastic cap over the bottom of the barrel. The barrel is hoisted vertically onto the boat and the bottom cap secured via waterproof tape.
- Excess tubing is cut off just above the sediment surface using a large pipe cutter, and any space between the sediment surface and the top of the barrel is filled with water to prevent sloshing and disruption of the surface during transport. A top cap is placed on the barrel and sealed with waterproof tape.
- If a replicate core is taken, the replicate also is extracted following the same procedures in a-c above.
During the coring process we are very careful to not stand on or damage any organisms (coral, sponges, etc.) or to damage the substrate other than the actual hole from the coring. In many areas, the mud is so soft that the hole caves in/collapses immediately after extraction, and no visible sign of the core is left.
Data recorded at the time of coring include: 1) GPS location (recorded on at least two instruments); 2) water depth to the substrate; 3) water depth to the sediment in the barrel (items 2 & 3 allow calculation of compaction during the coring process); 4) water properties including salinity, temperature, dissolved oxygen, and pH.
Core processing:
Cores are transported vertically and most are x-rayed as soon as possible (sometimes in the field at local hospitals). Cores are extruded vertically using the piston in reverse to push the sediment out of the barrel into one or two centimeter slices (resembling hockey pucks). The slices are trimmed around the edges to remove any contaminants due to contact with the barrel, bagged and weighed. Wet and dry weights are obtained for each sample.
Processing procedures may vary slightly for each core, depending on the different analyses being conducted and these procedures are reported with results for individual cores. In general, all material is retained. Small (1 cm3) plugs of sediment are removed for palynological analyses and for archival purposes. The remainder of the sample is washed with distilled and deionized water through 63 and 850 micron nylon mesh sieves and all material passing through the sieves is trapped in buckets and allowed to settle out for a period of days or weeks. The water is then siphoned off and the fine (<63 micron) fraction is air dried on filter paper under a hood, then distributed for geochemical and geochronological analyses. The 63 and 850 micron fractions are dried in a 50 degree C oven and distributed for faunal analyses.
Modern Samples: Monitoring the modern environment serves two important purposes for our research in South Florida's estuaries. First, the data we obtain in the modern environment provide the proxy information to interpret our downcore/historical data. The more modern sites we observe over the widest possible range of environmental variables (eg. salinity, temperature, post-storm, etc.), the more accurately we can interpret the historical information in the cores. Second, observing changes in the present day ecosystem over the seasons, and as conditions vary from year to year (for example rainfall), provides a basis for predicting how the system will respond to the changes implemented by CERP. For these reasons, we have established a number of monitoring sites through out the estuaries.
Actual sampling methods and frequencies vary from site to site, depending on the substrate, water depth, and conditions, and the specific purpose of the sampling. In some cases we have collected small push core samples (10 cm deep by 2"diameter); in others, small samples of vegetation, scoops of sediment, or petite ponar grab samples. At every site we record information on water properties including salinity, temperature, dissolved oxygen, and pH, and where ever possible, we conduct a snorkel survey of the site listing presence/absence of various indicator macrofauna and flora.
Processing of modern samples follows procedures similar to the core samples, except the <63 micron fraction is rarely retained.
|
