Publication Details

Category Text Publication
Reference Category Journals
DOI 10.5194/hess-26-5817-2022
Licence creative commons licence
Title (Primary) How do inorganic nitrogen processing pathways change quantitatively at daily, seasonal and multi-annual scales in a large agricultural stream?
Author Huang, J.; Borchardt, D.; Rode, M.
Source Titel Hydrology and Earth System Sciences
Year 2022
Department ASAM
Volume 26
Issue 22
Page From 5817
Page To 5833
Language englisch
Topic T5 Future Landscapes
Abstract Instream nitrogen (N) processing consists of complex interacting and highly time-varying pathways. To understand the role of a large agricultural stream river reaches in processing N thoroughly, it is urgently needed to continuously quantify high temporal resolution N processing pathways, reflecting seasonal shifts and multi-annual overarching effects. To this end, the hydrodynamic and river water quality model WASP 7.5.2 was applied in the 27.4-km reach of the 6th order agricultural stream Lower Bode (central Germany) for 5 years (2014–2018). Paired high-frequency data (15-min interval) of discharge (Q), nitrate (NO3), dissolved oxygen (DO), and Chlorophyll-a at upstream and downstream stations were used as model boundaries and for model constraints. The WASP model simulated 15-minute intervals of Q, NO3 and DO with Nash-Sutcliffe-Efficiency values higher than 0.9 for calibration and validation, enabling the calculation of gross and net dissolved inorganic N (DIN) uptake and pathway rates on a daily, seasonal and multi-annual scale. Results showed daily DIN net uptake rate ranged from −17.4 mg N m−2 d−1 to 553.9 mg N m−2 d−1. The highest daily net uptake could reach almost 30 % of total input loading, which occurred at extreme low flow in summer 2018. The growing season (spring and summer) accounted for 91 % of the average net annual DIN uptake in the measured period. In spring, both the DIN gross and net uptake were dominated by the phytoplankton uptake pathway. In summer, benthic algae assimilation dominated the gross DIN uptake. Conversely, the reach became a DIN net source with negative daily net uptake values in autumn and winter, mainly because the release from benthic algae surpassed uptake processes. Over the five years, average DIN gross and net uptake rates were 124.1 and 56.8 mg N m−2 d−1, which accounted for only 2.7 % and 1.2 % of the total loadings the study reach in the Lower Bode, respectively. 5-year average gross DIN uptake decreased from assimilation by benthic algae through assimilation by phytoplankton to denitrification. Our study highlights the value of combining river water quality modelling with high-frequency data in obtaining reliable instream DIN-budget, which facilitates our ability to manage N in aquatic systems. This study provides a methodology that can be applied to any large stream to quantify N processing pathway dynamics and complete our understanding of N cycling.
Persistent UFZ Identifier
Huang, J., Borchardt, D., Rode, M. (2022):
How do inorganic nitrogen processing pathways change quantitatively at daily, seasonal and multi-annual scales in a large agricultural stream?
Hydrol. Earth Syst. Sci. 26 (22), 5817 - 5833 10.5194/hess-26-5817-2022