Ecosystem Metabolic Rates Estimated from Diel Oxygen Measurements in Two Subtropical Estuaries

Area of Science:

• Estuarine Ecology
• Biogeochemical Cycling
• Climate Change Impacts

Background:

• Subtropical estuaries face increasing pressures from human activities and climate change.
• Carbon cycling in these ecosystems is not well understood, hindering effective management.
• Accurate measurements of ecosystem metabolism are needed to assess estuarine health.

Purpose of the Study:

• To compute gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) in Biscayne Bay and Tampa Bay.
• To understand the factors influencing carbon cycling in these subtropical estuaries.
• To provide updated productivity estimates for Biscayne Bay.

Main Methods:

• Dissolved oxygen diurnal cycles were measured over three years using 38 week-long deployments.
• Calculations of GPP, ER, and NEP were performed based on oxygen flux.
• Statistical analyses were used to identify correlations between production and environmental factors.

Main Results:

• On average, GPP and ER nearly balanced in both estuaries, with NEP being an order of magnitude smaller.
• Mean GPP was consistent across both bays (approx. 190 mmol O2 m-2 d-1), despite different dominant producers and nutrients.
• GPP correlated with temperature in Biscayne Bay and salinity in Tampa Bay.

Conclusions:

• Subtropical estuaries exhibit near-balanced production and respiration, indicating a sensitive carbon balance.
• Environmental factors like temperature and salinity significantly influence estuarine productivity.
• Frequent production measurements are essential for monitoring these dynamic ecosystems, especially under climate change.