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Metabolism and soil water viscosity control diel patterns of nitrate and DOC in a low order temperate stream

350 210 Stroud Water Research Center

Oviedo-Vargas, D., M. Peipoch, and C. Dow. 2022. Journal of Geophysical Research: Biogeosciences 127(5), e2021JG006640.

https://doi.org/10.1029/2021JG006640

Abstract

Dissolved organic carbon (DOC) and nitrate are key components of natural waters. Nitrate is an essential nutrient and DOC a major source of energy for aquatic microorganisms. Current field sensor technologies allow us to examine how these substances change temporally in streams and rivers at much greater resolution than manually-collected samples. Using field sensors we measured DOC and nitrate concentrations in White Clay Creek at high frequency (5-min intervals) during 2018. Our focus was to investigate how these solutes behaved at baseflow conditions, when the influence of storm events is minimal. We found that both DOC and nitrate concentrations showed diel (24-hr periods) oscillations with patterns that varied across seasons. In the spring, the diel changes were largely the result of the metabolic activity of stream microorganisms. However, in winter, daily changes in air temperature modulated the movement of DOC-rich and nitrate-poor soil water to the stream through a process known as “viscosity effect.” Results from our work contribute to our understanding of how stream ecosystems function, and are among the first to document the viscosity effect as a major driver of DOC and nitrate dynamics in streams.