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| Titel |
Attempting to link hydro-morphology, transient storage and metabolism in streams: Insights from reactive tracer experiments |
| VerfasserIn |
Marie J. Kurz, Christian Schmidt, Phillip Blaen, Julia L. A. Knapp, Jennifer D. Drummond, Eugenia Marti, Jay P. Zarnetske, Adam S. Ward, Stefan Krause |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133389
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| Publikation (Nr.) |
 EGU/EGU2016-13994.pdf |
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| Zusammenfassung |
| In-stream transient storage zones, including the hyporheic zone and vegetation beds, can be
hotspots of biogeochemical processing in streams, enhancing ecosystem functions such as
metabolism and nutrient uptake. The spatio-temporal dynamics and reactivity of these storage
zones are influenced by multiple factors, including channel geomorphology, substrate
composition and hydrology, and by anthropogenic modifications to flow regimes and nutrient
loads. Tracer injections are a commonly employed method to evaluate solute transport and
transient storage in streams; however, reactive tracers are needed to differentiate
between metabolically active and inactive transient storage zones. The reactive stream
tracer resazurin (Raz), a weakly fluorescent dye which irreversibly transforms to
resorufin (Rru) under mildly reducing conditions, provides a proxy for aerobic
respiration and an estimate of the metabolic activity associated with transient storage
zones.
Across a range of lotic ecosystems, we try to assess the influence of stream channel
hydro-morphology, morphologic heterogeneity, and substrate type on reach (103 m) and
sub-reach (102 m) scale transient storage, respiration, and nutrient uptake. To do so, we
coupled injections of Raz and conservative tracers (uranine and/or salt) at each study site. The
study sites included: vegetated mesocosms controlled for water depth; vegetated and
un-vegetated sediment-filled mesocosms fed by waste-water effluent; a contrasting sand- vs.
gravel-bedded lowland stream (Q = 0.08 m3/s); and a series of upland streams with
varying size (Q = 0.1 - 1.5 m3/s) and prevalence of morphologic features. Continuous
time-series of tracer concentrations were recorded using in-situ fluorometers and EC
loggers. At the stream sites, time-series were recorded at multiple downstream
locations in order to resolve sub-reach dynamics. Analyses yielded highly variable
transport metrics and Raz-Rru transformation between study sites and between
sub-reaches within stream sites. Higher Raz-Rru transformation rates were typically
observed in smaller streams, in sub-reaches with higher prevalence of morphologic
features known to promote hyporheic exchange, and in mesocosms with higher
water depth, vegetation density and retention time. However, relationships between
transformation rates and common metrics of transient storage were not consistent
among study cases, indicating the existence of yet unrealized complexities in the
relationships between water and solute transport and metabolism. Further insights
were also gained related to the utility of Raz and improved tracer test practices. |
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