Temporal Variation in River Nutrient Concentrations and the Impact of Storm Runoff on Hood Canal

Abstract

A year-long data set measuring dissolved nutrient, particulate nutrient, and dissolved lignin phenol concentrations in several temperate Pacific Northwest rivers, shows a strong correlation between river discharge rates and nutrient concentrations during significant storm events following a long dry period. Furthermore, dissolved lignin concentrations increase with river discharge during autumn and winter storms; systematic changes to C/V, S/V, and Ad/Al (v) ratios indicate a mobilization of relatively more woody/gymnosperm-derived and degraded material during storm events. Results from this study suggest that a shallow nutrient-rich pool of particulate matter accumulates in watersheds during long dry periods; this nutrient-rich particulate matter degrades in surface soils, creating a pool of accumulated dissolved nutrients in surface soils during periods of soil-saturation deficiency. Surface runoff during autumn and winter storms mobilizes the nutrient-rich particulate pool, whereas dissolved nutrients are mobilized from soils once the soil saturation deficiency is alleviated. This pool of shallow soil nutrients, secondary to a deep soil pool sustaining base flow conditions, is exhausted with successive winter storms; by spring there is little to no response in river nutrient concentrations and a dilution of dissolved lignin concentrations with increased rainfall and river flow.