Environmental Engineering Reference
In-Depth Information
surface of the tile; the sediment is collected, dried, and weighed to produce a mass
estimate. Ceramic tiles produced for home use (e.g., glazed kitchen tiles) are
appropriate. Ceramic tiles placed on the soil surface will suffice for wetlands
subject to low energy flooding. For high energy floodplains or tidal marshes, the
sediment collection tile should be anchored to the soil. For sites that are subject to
relatively deep flooding such as tidal marshes, tiles may be placed at several
elevations relative to the soil surface to determine sediment availability within
the water column. This is particularly important if the goal is to separate
re-suspended sediments (defined as the amount of sediments lifted 6 cm or more
above the sediment surface) from unsuspended, shifting surface material. Tiles may
be easily positioned at specific heights relative to the soil surface by attaching PVC
pipe to the base of the tile and inserting the pipe into the soil. Tiles are retrieved
when the soil surface is exposed to air, usually at 2 week or 1 month intervals.
Plant tissue is first removed from each tile. Sediment is scraped and rinsed off the
tiles and into sample cups using a rubber scraper and deionized water. Samples are
returned to the lab, filtered through pre-weighed paper filters, dried and weighed.
Sediment deposition is commonly reported as g dry weight/m
2
. Organic matter is an
important constituent of sediment in many depositional settings; its content in a
sediment sample can be determined by measuring weight loss in subsamples after
burning at selected temperatures (see
Soil Organic Matter: Loss on Ignition
above).
The following approach was presented by Pasternack and Brush (
1998
) and at
http://pasternack.ucdavis.edu/sedtiles.htm
.
The major advantages of this sturdier
design is that it lends itself to high energy tidal marshes and can be used to assess
erosion as well as accretion. It utilizes an aluminum pipe (1 m long
2 cm dia.)
'anchor' sunk into the ground and capped with a detachable ceramic tile flush with
the marsh surface. A plastic tube is attached to the bottom of each tile; the tube
drops over the anchor pipe. This provides a stable tile surface that is not susceptible
to motion unless subjected to extreme lift forces. Therefore, it is conducive to high
energy tidal marshes. They constructed the tile and tube assembly by attaching
(with plastic cement) a 7.5 cm long hard plastic pipe with an inner diameter of 2 cm
to the center of a plastic square with plastic cement. Schedule 77 plastic is
appropriate for the pipe and the square. The other side of the plastic square was
attached to the bottom of a 20 cm
20 cm glazed-ceramic tile with silicone glue.
Each sampling point should be marked by GPS. Even so, it may be difficult to
find the anchor in subsequent visits. One approach is to mark each anchor with a
second anchor as follows: Lay a meter stick on the ground with one end on the
anchor and the other pointing to a pre-determined compass direction (e.g., due east)
and hammer a second anchor ~0.5 m down into the ground at the east end of the
meter stick. Flag the top of this second anchor (marker anchor) with a long strip of
flagging attached with duct tape. Attach the tile assembly over the sunken auger by
placing the plastic pipe over the metal pipe. The metal pipe may need to be filed to
accommodate the plastic pipe.
The most appropriate sampling interval for sediment tiles depends on the
hydrodynamics and sediment loading rate of the system in question. Extra care is
needed when sampling very small or very large amounts of deposition. Pasternack
