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Abstract
We conducted a high-resolution observational study of nutrient dynamics in the Columbia River estuary using autonomous sensors measuring nitrate + nitrite, ammonium, phosphate, silicic acid, and nitrite across seasons in 2010. Large salinity gradients enabled calculation of river and ocean end members, revealing the estuary’s role as a “bioreactor” for inorganic nutrients despite short residence times. Elevated ammonium and phosphorus during late summer indicate localized remineralization in turbidity zones and lateral bays. Additionally, synchronous pulses of silicic acid and ammonium during spring tides suggest benthic diatom dissolution. These findings underscore estuarine biogeochemical complexity and its influence on nutrient cycling.