Water table wells (four per plot) constructed of 3.8 cm perforated PVC
pipe were installed to 1.0 m below the ground surface in pairs
perpendicular to the stream, each approximately five meters from the
thalweg. The paired well transects are between 200 and 800 meters
apart along the stream. Wells were installed by hand auguring to the
desired depth, inserting the well casing, backfilling with clean sand
to the top of the slots, then backfilling to within 15 cm of the
surface with native fill, and filling the remaining hole with
bentonite pellets. The wells were capped.
In October 2010, the Oregon Ridge site wells were replaced with larger
diameter 5.0 cm perforated PVC pipe installed to a depth of between
1.5 and 2 meters. There are now four wells at each transect at Oregon
Ridge for a total of eight wells at that site.
Water table levels are measured at one to four week intervals using a
flashlight and folding rule. When wells were dry the maximum
measurable depth (~1000 cm) was recorded. The well is first drained of
standing water. Recharge time of a minimum of 10 minutes is given
before collecting samples. The new deeper, larger diameter, wells at
Oregon Ridge do not drain with the pump as the recharge is too strong
so we instead draw off three liters of water from these wells before
sampling.
Samples for chemical analysis are pumped into a stoppered flask. The
stopper of the flask is fitted with an attachment for a 60 ml HDPE
bottle such that sample fills the bottle and then overflows into the
flask. The sample in the bottle is used for chemical analyses while
the overflow in the flask is measured for total volume. After one well
has been sampled, the tubing through which the sample is pumped is
rinsed with deionized water before the next bottle is attached for
sampling for chemical analysis at the next well.
Samples are stored with freezer packs while in the field. At the BES
laboratory samples are syringe filtered using 25mm Whatman GF/F
filters. Samples are refrigerated at 4 deg C and sent regularly to
Cary Institute of Ecosystem Studies in Millbrook, NY for colormetric
analysis of nitrate, ammonium and phosphate.
