EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Reservoir water quality deterioration due to deforestation emphasizes the indirect effects of global change

Michael Rode1, Xiangzhen Kong2,3, Salman Ghaffa1, Maria Determann2, Kurt Friese2, Seifeddine Jomaa1, Chenxi Mi2, Tom Shatwell2, and Karsten Rinke2
Michael Rode et al.
  • 1Helmholtz Centre for Environmental Research - UFZ, Department of Aquatic Ecosystem Analysis and Management, Magdeburg, Germany (
  • 2Helmholtz Centre for Environmental Research-UFZ, Department of Lake Research, Magdeburg, Germany
  • 3State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China

Deforestation is currently a widespread phenomenon and a growing environmental
concern in the era of rapid climate change. In temperate regions, it is challenging to
quantify the impacts of deforestation on the catchment dynamics and downstream
aquatic ecosystems such as reservoirs and disentangle these from direct climate
change impacts, let alone project future changes to inform management. Here, we
tackled this issue by investigating a unique catchment-reservoir system with two
reservoirs in distinct trophic states (meso- and eutrophic), both of which drain into the
largest drinking water reservoir in Germany. Due to the prolonged droughts in 2015-
2018, the catchment of the mesotrophic reservoir lost an unprecedented area of forest
(exponential increase since 2015 and ca. 17.1% loss in 2020 alone). We coupled
catchment nutrient exports (HYPE) and reservoir ecosystem dynamics (GOTM-WET)
models using a process-based modelling approach. The coupled model was validated
with datasets spanning periods of rapid deforestation, which makes our future
projections highly robust. Results show that in a short-term time scale (by 2035),
increasing nutrient flux from the catchment due to vast deforestation (80% loss) can
turn the mesotrophic reservoir into a eutrophic state as its counterpart. Our results
emphasize the more prominent impacts of deforestation than the direct impact of
climate warming in impairment of water quality and ecological services to downstream
aquatic ecosystems. Therefore, we propose to evaluate the impact of climate change
on temperate reservoirs by incorporating a time scale-dependent context, highlighting
the indirect impact of deforestation in the short-term scale. In the long-term scale (e.g.
to 2100), a guiding hypothesis for future research may be that indirect effects (e.g., as
mediated by catchment dynamics) are as important as the direct effects of climate
warming on aquatic ecosystems.

How to cite: Rode, M., Kong, X., Ghaffa, S., Determann, M., Friese, K., Jomaa, S., Mi, C., Shatwell, T., and Rinke, K.: Reservoir water quality deterioration due to deforestation emphasizes the indirect effects of global change, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5239,, 2023.