Estimating ecosystem metabolism from continuous multi-sensor measurements in the Seine River

Area of Science:

• Environmental Science
• River Ecology
• Biogeochemistry

Background:

• Large rivers play a crucial role in the global carbon cycle.
• Water quality degradation in rivers is widespread, yet river metabolism dynamics remain poorly understood.
• Anthropized rivers, like the Seine, face complex environmental pressures impacting their ecological functions.

Purpose of the Study:

• To assess the temporal variability of gross primary production (GPP) and ecosystem respiration (ER) in the Seine River over an annual cycle.
• To identify the key drivers influencing river metabolism.
• To understand the impact of human pressures on riverine ecosystem processes.

Main Methods:

• Continuous multi-sensor measurements were employed to monitor GPP and ER rates.
• Multivariate statistical analyses were used to determine the factors controlling river metabolism.
• Chlorophyll a (Chla), water temperature (T), light, and rainfall data were integrated into the analysis.

Main Results:

• The Seine River exhibits net heterotrophy annually (-226 gO2 m-2 year-1) but shows net autotrophy during seasonal phytoplankton blooms.
• Daily GPP is primarily driven by Chla, water temperature, light, and rainfall.
• Ecosystem respiration (ER) is mainly controlled by water temperature and Chla.
• Combined sewer overflows, exacerbated by storm events, increase ER and net heterotrophy.

Conclusions:

• River metabolism is regulated by multiple factors across different timescales, many of which are influenced by human activities.
• Continuous monitoring is essential for understanding how river ecosystems respond to evolving human pressures and climate change.
• The study highlights the sensitivity of riverine carbon cycling to anthropogenic impacts and environmental variability.