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A) Supplies:

1) Marker Horizon - There are many materials which you can use for a marker horizon. Brick dust, Grog, Sand, Kaolin, glitter and varieties of feldspar clay are all suitable for marker horizons. We have settled on using feldspar clay. Feldspar is a brilliant white material which forms a nice cohesive layer once it gets wet and is easily distinguishable from the surrounding sediment. We used to buy a specific variety called G200 from the Feldspar Corporation but it may no longer be available. You will need to check with a local supplier to see what is available. Feldspar typically comes in 50 LB bags. From a single bag you can expect to get about 6 feldspar plots (50cm x 50 cm) established.

Feldspar G200
Feldspar G200

Feldspar clay will work in most environmental settings. As with all marker horizons you will have the most problems in high energy areas (marker gets washed away) and in very low energy areas (marker never gets buried and washes away). Bioturbation by crabs or burrowing shrimp may also be a problem. In some instances a larger grain size material like sand may work better than the smaller particles in feldspar. Trial and error will be the only way to find the best marker for a given situation. Be aware that in almost all situations, the marker horizon will disappear over time. This is about the only certainty with this technique. You may need to add additional plots in the future.

2) 1/2" PVC or fiberglass stakes - To mark the boundaries of the plot containing the marker horizon. The stakes are about 2-4' in length. You may need longer stakes if you are working in a pond.

3) Respirator - These materials should not be inhaled so a high quality respirator is recommended when establishing the marker horizons.

B) Establishing the Marker Horizons

It is VERY important that the Feldspar Plots are established when you take your first (baseline) SET readings.

Feldspar Plots 1 Feldspar Plots 2

1) Three or four feldspar plots are usually deployed on a given sampling platform. We have typically used 3 per platform. This leaves plenty of room to add additional plots in the future if the initial plots disappear.

2) Select where you want to put the feldspar plot. Don't make it too far from the platform or else it will be difficult to sample the plot in the future.

3) Make a wire (or pvc) frame to approximate the size of the feldspar plot. We typically make our plots 50 cm x 50 cm Lay the frame on the marsh. If you are laying feldspar in a pond or on a flooded marsh, we use trash cans with the bottom cut off to define the feldspar plot and aid in establishing the horizon. It helps to push the trash can into the surface a small amount to keep the feldspar from leaking out the sides.

Feldspar Diagram Closeup
Dry Surface Wet Surface

Feldspar Plot - Dry
Mudflat - Anacostia Park, DC USA.

Feldspar Plot - Pond
Pond - Delta NWR, LA, USA


Feldspar Plot Feldspar Plot - Pond
Establishing Marker Horizons on a Flooded Marsh

4) Using a small cup, sprinkle the feldspar on the marsh surface (or into the trash can). We get about 6 plots (50 cm x 50 cm) per 50 LB bag. If using a trashcan, you will need to wait at least 10-15 minutes (or longer) to allow the feldspar inside to settle to the bottom. Carefully remove the can when finished.

5) Mark the plots with 2 (or 4) pvc or fiberglass stakes. If the plot is vegetated use an extra stake to knock the feldspar off the plants.

Note: the marker horizon will hopefully get buried so you will need these stakes to find the plot in the future. If the site is periodically burned, you might want to consider using fiberglass stakes to mark the plots.

6) You are finished! Be sure to draw a detailed map in your data book showing the relative locations of the feldspar plots in case the PVC stakes are lost or buried.

 

U.S. Department of the Interior, U.S. Geological Survey, Patuxent Wildlife Research Center
URL: http://www.pwrc.usgs.gov/ | Last Updated:1 February 2010
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