Climate Change Drove the Decline in Yangtze Estuary Net Primary Production Over the Past Two Decades

Area of Science:

• Marine ecology
• Climate change research
• Carbon cycle studies

Background:

• Net primary productivity (NPP) is crucial for estuarine carbon budgets and is sensitive to climate change and human impacts.
• Understanding the spatiotemporal dynamics of NPP in the Yangtze Estuarine-offshore continuum (YEOC) is vital for regional carbon assessments.

Purpose of the Study:

• To quantify NPP trends and identify driving factors in the YEOC over the past two decades.
• To assess the impact of climate change and anthropogenic disturbances on YEOC's carbon sequestration capacity.

Main Methods:

• Combined remote sensing and machine learning (ML) approach to measure NPP.
• Analysis of temporal NPP trends (2002-2022) and correlation with climate and anthropogenic factors.

Main Results:

• Average NPP in YEOC was 273.19 ± 21.26 mgC m^-2 day^-1, showing a significant downward trend from 2002 to 2022.
• Climate factors (fluctuations, sea level rise, discharge) explained 65% of NPP variation by influencing phytoplankton biomass and photosynthesis rates.
• Anthropogenic disturbances (damming, nutrient emissions) showed no significant impact on NPP.

Conclusions:

• Climate change is the primary driver of NPP spatiotemporal transformation in the YEOC.
• Decreased NPP has reduced the estuary's carbon sink capacity, impacting biological carbon fixation.
• Findings enhance understanding of estuarine carbon budget responses to environmental changes.