Wastewater inputs reduce the CO₂ uptake by coastal oceans

Area of Science:

• Marine chemistry
• Oceanography
• Environmental science

Background:

• Coastal oceans play a crucial role in global carbon dioxide (CO2) uptake.
• The impact of wastewater on the CO2 balance of coastal ecosystems remains poorly understood.
• Jiaozhou Bay (JZB) is a temperate coastal bay significantly influenced by wastewater inputs.

Purpose of the Study:

• To investigate the sea surface CO2 partial pressure (pCO2) and air-sea CO2 flux in Jiaozhou Bay.
• To understand the influence of wastewater on CO2 dynamics in a temperate coastal bay.
• To determine whether Jiaozhou Bay acts as a CO2 source or sink.

Main Methods:

• Monthly surveys of sea surface pCO2 and related parameters were conducted over one year (April 2014-March 2015).
• Spatial and temporal variations in surface pCO2 were analyzed.
• Air-sea CO2 flux was calculated to assess the bay's net CO2 exchange with the atmosphere.

Main Results:

• Surface pCO2 in JZB exhibited significant temporal and spatial variability (163–1222 μatm, annual average 573 μatm).
• The bay was oversaturated with CO2 from April to December, particularly in the northeast where wastewater diluted salinity.
• JZB acted as a net CO2 source to the atmosphere (9.6 ± 10.8 mmol C m⁻² d⁻¹).

Conclusions:

• Wastewater inputs, direct CO2 addition, and organic matter degradation contribute to high pCO2 in JZB.
• Sea surface temperature influences monthly pCO2 variations, while wastewater and biological activity drive spatial differences.
• Reducing wastewater discharge is crucial for enhancing CO2 uptake in coastal oceans.