End-member river water composition in the acidified Adirondack Region, Northern New York, USA

•Raquette River water was sampled at 17 locations during high and low flow events.•During average flow chemical variation corresponded to bedrock distribution.•During event conditions downriver hydrochemical trends were muted.•Baseflow and precipitation pH controls event hydrochemistry.•A dolostone quarry along the river alters river chemistry during stormflow.

Study regionFrom its headwaters in the Adirondacks to its confluence with the St. Lawrence River, the Raquette flows across acidic crystalline rock, a marble dominated metasedimentary sequence, and Paleozoic sedimentary rocks with increasing capacity to neutralize acidity. Although its drainage basin is largely forested and has a limited population, seventeen hydroelectric reservoirs occur along its mid to lower reaches.Study focusThe goal of the study was to document the geochemistry of Raquette River waters during discharge events. The river was sampled for 69 elements and 7 anions, along its length during stormflow associated with Tropical Storm Irene. One year later the same sites were sampled during a drought with a flow-duration percentage was 98.65.New hydrological insights for the regionSamples collected during average discharge volumes documented chemical gradients corresponding to bedrock spatial distribution. These trends were muted during both stormflow and baseflow, and imply that other factors influence water chemistry during high and low-flow events. Our study documents an example of event river chemistry responding less to extremes of flow or variation in underlying geology than anticipated. During the stormflow sampling one sample had elevated specific conductance (160.4 μS cm−1) and pH (8.21). This data, anomalous geochemistry, and images from Google Earth suggest that the river chemistry is sporadically impacted by discharge from a dolostone quarry located 6 km upstream during runoff events.