Preprints
https://doi.org/10.5194/egusphere-2025-642
https://doi.org/10.5194/egusphere-2025-642
21 Feb 2025
 | 21 Feb 2025

Will groundwater-borne nutrients affect river eutrophication in the future? A multi-tracer study provides evidence

Julia Zill, Axel Suckow, Ulf Mallast, Jürgen Sültenfuß, and Christian Siebert

Abstract. Groundwater can be a major source of nutrients and contaminants to river systems in agriculturally active areas with significant implications for water quality and ecosystem health. The Elbe river in eastern Germany, characterised by Cretaceous aquifers upstream and Quaternary aquifers downstream, is located in areas of intense agricultural activity and is therefore vulnerable to nutrient fluxes. This study investigates the time scales of diffuse groundwater-borne nutrients entering the river using multi-environmental tracers (³H/³He, SF₆, CFCs, ¹⁴C). By applying lumped parameter models, we concluded on time scales of groundwater flow from recharge to the river ranging from 0 to 41 years, with infiltration occurring predominantly after 1985. Our results highlight a young groundwater system with measurable denitrification and minimal to moderate admixtures of older water fractions clearly discernible with helium. This suggests that the legacy of nutrient inputs from intensive fertilisation during the GDR period (1945–1989) has already peaked, with groundwater-borne nutrient concentrations expected to decline over the coming decades. These results are crucial for informing river basin management strategies aimed at mitigating eutrophication and protecting aquatic ecosystems. It provides valuable insights into the temporal dynamics of groundwater contributions to surface waters and their regional implications for sustainable resource management.

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Julia Zill, Axel Suckow, Ulf Mallast, Jürgen Sültenfuß, and Christian Siebert

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-642', Anonymous Referee #1, 06 Apr 2025
    • AC1: 'Reply on RC1', Julia Zill, 25 Jun 2025
  • RC2: 'Comment on egusphere-2025-642', Matthew Currell, 31 May 2025
    • AC2: 'Reply on RC2', Julia Zill, 25 Jun 2025
Julia Zill, Axel Suckow, Ulf Mallast, Jürgen Sültenfuß, and Christian Siebert
Julia Zill, Axel Suckow, Ulf Mallast, Jürgen Sültenfuß, and Christian Siebert

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Short summary
Groundwater in agricultural regions can transport nutrients and contaminants into rivers, affecting water quality. This study examines nutrient flux in the german Elbe River using multi-environmental tracers. Groundwater takes a few decades to reach the river, mostly infiltrating after 1985. This means that massive nutrient inputs from past fertilization have peaked and will decline in the future. These findings guide management strategies to reduce eutrophication and protect aquatic ecosystems.
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