Establishing Marker Horizons

This page provides detailed instructions for installing the marker horizons used in conjunction with the SET.

Delta NWR, LA USA

Big Thicket NP, TX USA

Tijuana Slough NWR, CA USA

Marker horizons are used to quantify surface deposition and erosion on a marsh surface or pond bottom (more information)

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. For most situations, we have settled on using G-200 feldspar clay from the Feldspar Corporation. It comes in 50 LB bags and we typically get about 6 feldspar plots (50cm x 50 cm) from a single bag. This is a brilliant white material which forms a nice cohesive layer once it gets wet and is easily distinguishable from the surrounding sediment.

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 stakes - To mark the boundaries of the plot containing the marker horizon. The stakes are about 3' 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 plot locations with an SET pipe.

Feldspar - No SET pipe

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. This is very difficult if you are working on a flooded marsh surface. Regardless, try to minimize leaking of the feldspar.

Dry Surface Anacostia Park NPS, DC USA. Fire Island NS, NY USA	Wet Surface Delta NWR, LA USA Delta NWR, LA USA Fire Island NS, NY USA

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 stakes. If the plot is vegetated use the PVC 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 rebar or fireproof PVC to mark the plots.

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