Synoptic Stream Water Chemistry - README

1. Overview

This dataset contains dissolved solute concentrations from synoptic stream water chemistry sampling conducted across five watersheds as part of the Quantify ecosystem exports across space and time (QuEST) project.

The five study watersheds span a range of climates, geologies, and land uses across the contiguous United States:

Grab samples were collected at up to 115 sites across the five watersheds during synoptic campaigns. This resource covers 2023–2026 published separately in water years within this same HydroShare resource.

2. Files in this resource

3. Related resources in the QuEST collection

This dataset is part of a larger collection of QuEST project data on HydroShare. Related resources include:

• Continuous and instantaneous discharge — Instantaneous discharge measurements were taken concurrently with water chemistry at a subset of sites. Full discharge records are published as a separate resource. Files can be joined to this dataset using Watershed + Site + Date.

• Continuous sensor (SCAN) data — Optical sensor data (absorbance) collected at a subset of sites. The chemistry data in this resource was used to calibrate SCAN-derived solute concentration estimates. See the SCAN resource for calibration details and cross-reference by Watershed + Site + Date.

Cross-reference note: All resources in the QuEST collection share Watershed, Site, and Date as common keys for joining across datasets.

4. Methods

Sample collection

Grab samples were collected by hand at stream sites during synoptic campaigns in which all sites within a watershed were sampled within a short time window (typically 1–2 days). Sample type is recorded in the Sample_Type column:

• stream — in-channel grab sample
• snow — snowmelt or snowpack sample
• rain — precipitation sample

At sites where duplicate samples were collected on the same date, values were averaged prior to publication. The n_reps column records how many replicates were averaged into each row.

Laboratory analysis

Samples were analyzed at the University of New Hampshire Water Quality Analysis Laboratory.

Note on NO3: Arkansas samples were analyzed using the NO3+NO2 colorimetric method (MDL = 0.010 mg N/L). All other watersheds used ion chromatography (MDL = 0.005 mg N/L). The NO3_method column records which method was applied to each row. These values are not directly comparable across watersheds without accounting for this difference.

Below-detection substitution

Values below the MDL were replaced with one-half the MDL (MDL/2), following standard practice for environmental chemistry data. The {analyte}_belowMDL flag column records which values were substituted:

• TRUE = value was below MDL and has been replaced with MDL/2
• FALSE = reported value is at or above MDL

Replicate averaging and variability

Where multiple replicates were collected at the same site on the same date, concentrations were averaged to produce one row per site × date. The n_reps column records the number of replicates averaged (value of 1 = single sample, no averaging).

The high_RPD column flags rows where replicate agreement was poor, using the relative percent difference (RPD = |A − B| / mean(A, B) × 100). A row is flagged TRUE if RPD exceeded 15% AND the mean value was above 10× the MDL for that analyte, following the UNH lab QC protocol. High RPD near the detection limit is analytically expected and is not flagged. Rows with n_reps = 1 are always FALSE.

5. Column descriptions