High flow and flood events are important components of natural river flow regimes, as they maintain healthy aquatic habitats and riparian ecosystems. However, human alteration of rivers for flood control, including dam construction, modifies and homogenizes downstream hydrological patterns by moderating extreme high and low flows. In this study, we evaluate the biogeochemical fluxes stemming from the first experimental spring flood (i.e., pulse event) on the Allegheny River (Pennsylvania, USA) conducted by the United States Army Corps of Engineers as part of the Sustainable Rivers Project. The pulse event was initiated on March 30, 2023, by a sustained release of 451 cms from the Kinzua Dam for 21 hours. We hypothesized that this experimental spring pulse would initially lead to the release of organic-rich sediment and nutrients stored behind the Kinzua Dam. We also expected the "geochemical fingerprint" of downstream water to change over the duration of the pulse event due to the released flood water interacting with hyporheic water, scouring the channel and riparian areas, and then ultimately receding. To quantify the impact of the pulse on downstream biogeochemistry, we collected hourly water grab samples over a 48-hour period that spanned pre- and post-pulse conditions from multiple locations downstream of the Kinzua Dam. We evaluated the water chemistry of grab samples for multiple parameters, including concentrations of dissolved metals, nutrients, total suspended solids, and nitrate isotopes. Our results indicate that variable water chemistries can be linked to the timing and flushing of different portions of the river channel and floodplain across the span of the pulse event. These results demonstrate the value of downstream monitoring during pulse events for tracing flow dynamics, quantifying material fluxes, and documenting the impact of similar experimental spring floods on downstream river ecosystems.

This resource includes the data files of: environmental measurements (including but not limited to water temperature, pH, conductivity); hourly grab sample concentrations of dissolved metals, nutrients, total suspended solids, and nitrate isotopes; United States Geological Survey gage streamflow during the pulse event; and code associated with organizing data and calculations.