Riparian Microtopography Affects Event‐Driven Stream DOC Concentrations and DOM Quality in a Forested Headwater Catchment

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Blaurock, Katharina ; Garthen, Phil ; da Silva, Maria P. ; Beudert, Burkhard ; Gilfedder, Benjamin Silas ; Fleckenstein, Jan ; Peiffer, Stefan ; Lechtenfeld, Oliver J. ; Hopp, Luisa:
Riparian Microtopography Affects Event‐Driven Stream DOC Concentrations and DOM Quality in a Forested Headwater Catchment.
In: Journal of Geophysical Research: Biogeosciences. Bd. 127 (2022) Heft 12 . - e2022JG006831.
ISSN 2169-8961
DOI: https://doi.org/10.1029/2022JG006831

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Abstract

The transport of dissolved organic carbon (DOC) from the soils to inland waters plays an
important role in the global carbon cycle. Widespread increases in DOC concentrations have been observed
in surface waters over the last few decades, affecting carbon balances, ecosystem functioning and drinking
water treatment. However, the primary hydrological controls on DOC mobilization are still uncertain. The aim
of this study was to investigate the role of microtopography in the riparian zone for DOC export and DOM
quality. DOC concentration and DOM quality in the shallow groundwater of a riparian zone and in streamflow
in a forested headwater catchment was investigated using fluorescence and absorbance characteristics. We
found higher DOC concentrations with a higher aromaticity in the microtopographical depressions, which
were influenced by highly dynamic shallow groundwater levels, than in the flat forest soil. As a result of the
frequent wet-dry cycles in the upper soil layers, aromatic DOC accumulated in the shallow groundwater within
and below the microtopographical depressions. Rising groundwater levels during precipitation events led to the
connection of the microtopographical depressions to the stream, resulting in a change toward more aromatic
DOC in the stream. Increasing stream DOC concentrations were accompanied by increasing concentrations
of iron and aluminum, suggesting the coupled release of these metals with DOC from the riparian zone. Our
results highlight the importance of the interplay between microtopography and groundwater level dynamics in
the riparian zone for DOC export from headwater catchments.