Toward Understanding of Long‐Term Nitrogen Transport and Retention Dynamics Across German Catchments. Issue 24 (14th December 2022)

• Record Type: Journal Article
• Authors: Nguyen, Tam V.; Sarrazin, Fanny J.; Ebeling, Pia; Musolff, Andreas; Fleckenstein, Jan H.; Kumar, Rohini
• Is Part Of: Geophysical research letters. Volume 49:Issue 24(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-14
• Subjects: nitrogen legacies -- large‐sample assessment -- nitrogen transport and retention; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL100278
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Long‐term nitrogen (N) transport and retention dynamics across catchments are not well understood. Using a process‐based model for 89 German catchments, results across study catchments reveal that most N surplus (during 1950–2014) was removed by denitrification (mean ± standard deviation: 58 ± 15%) while the remaining fraction was mostly stored in the soil (14% ± 11%). The mean groundwater transit times in these catchments varied from 3.2 to 20.3 years. These results indicate that past N inputs could continue to affect surface and groundwater quality in the coming years. We identified four catchment groups with distinct archetypal N transport and retention dynamics, which are linked to the catchments' climate, topographic, and geological conditions. Overall, our results shed light on long‐term N dynamics in German catchments and how they are linked to catchment characteristics, emphasizing the role of long‐term N accumulation and transport for water quality management and evaluation programs. Plain Language Summary: High nitrate concentrations in German water bodies are quite common. It is unclear to what degree current nitrogen levels in water bodies are due to current or past nitrogen (N) application on agricultural fields. What happened to excess N (N was not taken up by plants) in catchments has not been fully understood. In this study, we modeled the fate of excess N in 89 German catchments during the period 1950–2014. Our results suggest that most of the excess N was removed from the catchment in gaseous form (denitrification), and a substantial portion of the remaining excess N was stored in the soil zone. This soil N can leach into the deeper zone (groundwater) where it may travel for 3–20 years to reach the catchment outlet. We also identified four distinct groups of catchments with different behavior in terms of N transport and storage, which further exhibited different climatic, topographic, and subsurface conditions, suggesting that these factors could play a role in catchment N transport and retention. Overall, our results show that there could be a substantial delay between implemented management practices and resulting changes in surface or groundwater quality, which should be considered in water quality management. Key Points: We provided insights into the long‐term (1950–2014) nitrogen (N) transport and retention across various German catchments Large‐sample assessment shows that 57% of N surplus was removed by denitrification and 15% of N surplus was accumulated in the soil zone Four catchment clusters with distinct nitrogen transport and retention dynamics were linked to climatic, topographic, and geological factors