Field and Laboratory Methods
Stream samples were collected manually for weekly, quarterly and decadal
sampling. Episodic high-flow samples were collected bi-hourly by
automated samplers when flows were equal to or above the 5% exceedance
for the respective season (high-flow season: Nov 15-May 14 and low-flow
season: May 15-Nov. 14). A subset of the collected automated event
samples were analyzed: all samples on the rising hydrograph limb and
20% selected from the falling hydrograph limb. Samples were analyzed
for acid neutralizing capacity (ANC), pH, calcium ion
(Ca2+), magnesium ion (Mg2+),
potassium ion (K+ ), sodium ion
(Na+) ammonium ion (NH+), sulfate
ion (SO42-), nitrate ion
(NO3-), chloride ion
(Cl-), silica (SiO2), and specific
conductance. A subset of samples were also evaluated for total monomeric
aluminum (AlTM), organic monomeric aluminum
(AlOM) and dissolved organic carbon (DOC). During the
analysis period, laboratory instrumentation was upgraded, and in some
cases, methods changed. The analytical methods and correction factors
used to align the older results with current instrumentation are
available at
https://swas.evsc.virginia.edu/POST/assets/docs/Methods.pdf.
Stream stage was measured hourly within a stilling well by an automated
system and was verified by staff readings during weekly site visits.
Routine manual discharge measurements were made with automated flow
meters and salt dilution gaging methods (low flow conditions), and
calculated with the Manning’s equation (high flow conditions). Measured
and calculated discharge were used to establish and maintain a rating
curve, updated annually, for calculation of continuous discharge.