In:
Biogeosciences, Copernicus GmbH, Vol. 16, No. 22 ( 2019-11-28), p. 4497-4516
Abstract:
Abstract. Increasing dissolved organic carbon (DOC) concentrations
and exports from headwater catchments impact the quality of downstream
waters and pose challenges to water supply. The importance of riparian zones
for DOC export from catchments in humid, temperate climates has generally
been acknowledged, but the hydrological controls and biogeochemical factors
that govern mobilization of DOC from riparian zones remain elusive. A
high-frequency dataset (15 min resolution for over 1 year) from a
headwater catchment in the Harz Mountains (Germany) was analyzed for
dominant patterns in DOC concentration (CDOC) and optical DOC quality
parameters SUVA254 and S275−295 (spectral slope between 275 and
295 nm) on event and seasonal scales. Quality parameters and CDOC
systematically changed with increasing fractions of high-frequency quick
flow (Qhf) and antecedent hydroclimatic conditions, defined by the
following metrics: aridity index (AI60) of the preceding 60 d and the
quotient of mean temperature (T30) and mean discharge (Q30) of the
preceding 30 d, which we refer to as discharge-normalized temperature
(DNT30). Selected statistical multiple linear regression models for the
complete time series (R2=0.72, 0.64 and 0.65 for
CDOC, SUVA254 and S275−295, resp.) captured DOC dynamics based on
event (Qhf and baseflow) and seasonal-scale predictors (AI60,
DNT30). The relative importance of seasonal-scale predictors allowed for
the separation of three hydroclimatic states (warm and dry, cold and wet,
and intermediate). The specific DOC quality for each state indicates a shift
in the activated source zones and highlights the importance of antecedent
conditions and their impact on DOC accumulation and mobilization in the
riparian zone. The warm and dry state results in high DOC concentrations
during events and low concentrations between events and thus can be seen as
mobilization limited, whereas the cold and wet state results in low
concentration between and during events due to limited DOC accumulation in
the riparian zone. The study demonstrates the considerable value of
continuous high-frequency measurements of DOC quality and quantity and its
(hydroclimatic) key controlling variables in quantitatively unraveling DOC
mobilization in the riparian zone. These variables can be linked to DOC
source activation by discharge events and the more seasonal control of DOC
production in riparian soils.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-16-4497-2019
DOI:
10.5194/bg-16-4497-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2158181-2
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