TY  - JOUR
A1  - Sarrazin, Fanny J.
A1  - Kumar, Rohini
A1  - Basu, Nandita B.
A1  - Musolff, Andreas
A1  - Weber, Michael
A1  - Van Meter, Kimberly J.
A1  - Attinger, Sabine
T1  - Characterizing catchment-scale nitrogen legacies and constraining their uncertainties
T2  - Water resources research
N2  - Improving nitrogen (N) status in European water bodies is a pressing issue. N levels depend not only on current but also past N inputs to the landscape, that have accumulated through time in legacy stores (e.g., soil, groundwater). 
Catchment-scale N models, that are commonly used to investigate in-stream N levels, rarely examine the magnitude and dynamics of legacy components. 

This study aims to gain a better understanding of the long-term fate of the N inputs and its uncertainties, using a legacy-driven N model (ELEMeNT) in Germany's largest national river basin (Weser; 38,450 km(2)) over the period 1960-2015. 
We estimate the nine model parameters based on a progressive constraining strategy, to assess the value of different observational data sets. 
We demonstrate that beyond in-stream N loading, soil N content and in-stream N concentration allow to reduce the equifinality in model parameterizations. 
We find that more than 50% of the N surplus denitrifies (1480-2210 kg ha(-1)) and the stream export amounts to around 18% (410-640 kg ha(-1)), leaving behind as much as around 230-780 kg ha(-1) of N in the (soil) source zone and 10-105 kg ha(-1) in the subsurface. 

A sensitivity analysis reveals the importance of different factors affecting the residual uncertainties in simulated N legacies, namely hydrologic travel time, denitrification rates, a coefficient characterizing the protection of organic N in source zone and N surplus input. 

Our study calls for proper consideration of uncertainties in N legacy characterization, and discusses possible avenues to further reduce the equifinality in water quality modeling.
KW  - nitrogen legacies
KW  - water quality modeling
KW  - equifinality
KW  - parameter
KW  - estimation
KW  - sensitivity analysis
Y1  - 2022
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/63886
SN  - 0043-1397
SN  - 1944-7973
VL  - 58
IS  - 4
PB  - American Geophysical Union
CY  - Washington
ER  -