Journal
WATER
Volume 11, Issue 11, Pages -Publisher
MDPI
DOI: 10.3390/w11112208
Keywords
unsteady-state discharge; solute transport; intermittent stream; diurnal discharge fluctuations; reactive tracers; headwaters; river corridor; hyporheic; resazurin
Categories
Funding
- Leverhulme Trust
- UK Natural Environment Research Council [NERC NE/L003872/1]
- European Commission [734317]
- National Science Foundation [DEB-1440409]
- National Science Foundation (NSF) awards [EAR 1652293, EAR 1417603, EAR 1846855, EAR 1446328]
- Department of Energy (DOE) award [DE-SC0019377]
- DOE's Office of Biological and Environmental Research via the Mercury Scientific Focus Area at Oak Ridge National Laboratory
- U.S. Department of Energy (DOE) [DE-SC0019377] Funding Source: U.S. Department of Energy (DOE)
- NERC [NE/L003872/1] Funding Source: UKRI
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Time-variable discharge is known to control both transport and transformation of solutes in the river corridor. Still, few studies consider the interactions of transport and transformation together. Here, we consider how diurnal discharge fluctuations in an intermittent, headwater stream control reach-scale solute transport and transformation as measured with conservative and reactive tracers during a period of no precipitation. One common conceptual model is that extended contact times with hyporheic zones during low discharge conditions allows for increased transformation of reactive solutes. Instead, we found tracer timescales within the reach were related to discharge, described by a single discharge-variable StorAge Selection function. We found that Resazurin to Resorufin (Raz-to-Rru) transformation is static in time, and apparent differences in reactive tracer were due to interactions with different ages of storage, not with time-variable reactivity. Overall we found reactivity was highest in youngest storage locations, with minimal Raz-to-Rru conversion in waters older than about 20 h of storage in our study reach. Therefore, not all storage in the study reach has the same potential biogeochemical function and increasing residence time of solute storage does not necessarily increase reaction potential of that solute, contrary to prevailing expectations.
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