Details zur Publikation

Referenztyp Zeitschriften
DOI / URL Link
Titel (primär) Trajectories of nitrate input and output in three nested catchments along a land use gradient
Autor Ehrhardt, S.; Kumar, R.; Fleckenstein, J.H.; Attinger, S.; Musolff, A.;
Journal / Serie Hydrology and Earth System Sciences
Erscheinungsjahr 2019
Department CHS; HDG;
Band/Volume 23
Heft 9
Sprache englisch;
POF III (gesamt) T31;
Datenlinks https://doi.org/10.4211/hs.9c57af9b5c1343bb840ba198a49ace1c
Supplements https://www.hydrol-earth-syst-sci.net/23/3503/2019/hess-23-3503-2019-supplement.pdf
Abstract

Increased anthropogenic inputs of nitrogen (N) to the biosphere during the last few decades have resulted in increased groundwater and surface water concentrations of N (primarily as nitrate), posing a global problem. Although measures have been implemented to reduce N inputs, they have not always led to decreasing riverine nitrate concentrations and loads. This limited response to the measures can either be caused by the accumulation of organic N in the soils (biogeochemical legacy) – or by long travel times (TTs) of inorganic N to the streams (hydrological legacy). Here, we compare atmospheric and agricultural N inputs with long-term observations (1970–2016) of riverine nitrate concentrations and loads in a central German mesoscale catchment with three nested subcatchments of increasing agricultural land use. Based on a data-driven approach, we assess jointly the N budget and the effective TTs of N through the soil and groundwater compartments. In combination with long-term trajectories of the CQ relationships, we evaluate the potential for and the characteristics of an N legacy.

We show that in the 40-year-long observation period, the catchment (270 km2) with 60 % agricultural area received an N input of 53 437 t, while it exported 6592 t, indicating an overall retention of 88 %. Removal of N by denitrification could not sufficiently explain this imbalance. Log-normal travel time distributions (TTDs) that link the N input history to the riverine export differed seasonally, with modes spanning 7–22 years and the mean TTs being systematically shorter during the high-flow season as compared to low-flow conditions. Systematic shifts in the CQ relationships were noticed over time that could be attributed to strong changes in N inputs resulting from agricultural intensification before 1989, the break-down of East German agriculture after 1989 and the seasonal differences in TTs. A chemostatic export regime of nitrate was only found after several years of stabilized N inputs. The changes in CQ relationships suggest a dominance of the hydrological N legacy over the biogeochemical N fixation in the soils, as we expected to observe a stronger and even increasing dampening of the riverine N concentrations after sustained high N inputs. Our analyses reveal an imbalance between N input and output, long time-lags and a lack of significant denitrification in the catchment. All these suggest that catchment management needs to address both a longer-term reduction of N inputs and shorter-term mitigation of today's high N loads. The latter may be covered by interventions triggering denitrification, such as hedgerows around agricultural fields, riparian buffers zones or constructed wetlands. Further joint analyses of N budgets and TTs covering a higher variety of catchments will provide a deeper insight into N trajectories and their controlling parameters.

ID 22215
dauerhafte UFZ-Verlinkung http://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=22215
Ehrhardt, S., Kumar, R., Fleckenstein, J.H., Attinger, S., Musolff, A. (2019):
Trajectories of nitrate input and output in three nested catchments along a land use gradient
Hydrol. Earth Syst. Sci. 23 (9), 3503 - 3524