TY  - JOUR
A1  - Nguyen, Tam
A1  - Kumar, Rohini
A1  - Musolff, Andreas
A1  - Lutz, Stefanie R.
A1  - Sarrazin, Fanny
A1  - Attinger, Sabine
A1  - Fleckenstein, Jan H.
T1  - Disparate Seasonal Nitrate Export From Nested Heterogeneous Subcatchments Revealed With StorAge Selection Functions
JF  - Water resources research
N2  - Understanding catchment controls on catchment solute export is a prerequisite for water quality management. StorAge Selection (SAS) functions encapsulate essential information about catchment functioning in terms of discharge selection preference and solute export dynamics. However, they lack information on the spatial origin of solutes when applied at the catchment scale, thereby limiting our understanding of the internal (subcatchment) functioning. Here, we parameterized SAS functions in a spatially explicit way to understand the internal catchment responses and transport dynamics of reactive dissolved nitrate (N-NO3). The model was applied in a nested mesoscale catchment (457 km(2)), consisting of a mountainous partly forested, partly agricultural subcatchment, a middle-reach forested subcatchment, and a lowland agricultural subcatchment. The model captured flow and nitrate concentration dynamics not only at the catchment outlet but also at internal gauging stations. Results reveal disparate subsurface mixing dynamics and nitrate export among headwater and lowland subcatchments. The headwater subcatchment has high seasonal variation in subsurface mixing schemes and younger water in discharge, while the lowland subcatchment has less pronounced seasonality in subsurface mixing and much older water in discharge. Consequently, nitrate concentration in discharge from the headwater subcatchment shows strong seasonality, whereas that from the lowland subcatchment is stable in time. The temporally varying responses of headwater and lowland subcatchments alternate the dominant contribution to nitrate export in high and low-flow periods between subcatchments. Overall, our results demonstrate that the spatially explicit SAS modeling provides useful information about internal catchment functioning, helping to develop or evaluate spatial management practices.
KW  - catchment nitrate export
KW  - StorAge Selection function
KW  - travel time distribution
KW  - mesoscale heterogeneous catchment
KW  - subcatchment response
Y1  - 2022
U6  - https://doi.org/10.1029/2021WR030797
SN  - 0043-1397
SN  - 1944-7973
VL  - 58
IS  - 3
PB  - American Geophysical Union
CY  - Washington
ER  -