Sediment communities from the hyporheic zone of the Columbia River along the Hanford Reach were sampled from April 30, 2014 to November 25, 2014, using sand packs deployed at three equivalent hyporheic zone locations approximately 100m apart along the river (T2, T3, and T4) for six weeks at a time [22]. Water chemistry data taken in parallel at the three sites showed similar, yet not identical temporal patterns. A mid-year shift in hydraulic regime was observed, with higher influx of surface water in the spring resulting in higher levels of dissolved organic carbon (measured as non-purgeable organic carbon) (NPOC) (0.8–1.0 mg/L) (Fig 2A) and low levels of nitrate (10–15 μM) (Fig 2B), transitioning to a more groundwater-influenced condition in the fall, increasing the nitrate concentrations (up to 300 μM) and decreasing NPOC concentration (down to <0.4 mg/L). Because the groundwater in this system is oxic, the DO concentration was fairly constant for the duration of sampling, ranging from ~60–100% saturation (Fig 2C). The water temperature followed expected seasonal trends, warming in the summer and cooling in the fall (Fig 2D). Sampling times were categorized as early (Apr 30 through Jul 22) or late (Sep 2 through Nov 30), based on these observations.
