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.