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

## TL;DR

This study estimates carbon cycling in two subtropical estuaries using oxygen measurements, revealing similar production rates despite different environmental conditions.

## Contribution

The study provides new, long-term metabolic rate estimates for subtropical estuaries using diel oxygen measurements.

## Key findings

- Gross primary production (GPP) and ecosystem respiration (ER) nearly balance in both estuaries.
- GPP estimates in Biscayne Bay are much higher than previous measurements from the 1970s.
- GPP correlates more with water temperature in Biscayne Bay and with salinity in Tampa Bay.

## Abstract

Subtropical estuaries worldwide are facing increasing pressure from human population growth, development, and climate change. Carbon is a useful currency for understanding how estuaries respond to these pressures and yet relatively little is known about carbon cycling in subtropical estuaries. Here we compute gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) from the diurnal cycle in dissolved oxygen measured during 38 week-long individual deployments over three years in two estuaries in the southeastern United States, Biscayne Bay and Tampa Bay. On average for both estuaries, GPP and ER nearly balance, with NEP about an order of magnitude smaller. Even though production in Tampa Bay and Biscayne Bay is dominated by different primary producers and limiting nutrients, mean GPP was the same, about 190 mmol O2 m–2 d–1 (570 g C m–2 y–1). Our GPP estimates for Biscayne Bay are more than an order of magnitude greater than the only other productivity estimates available for this system, which are planktonic net primary productivity measurements from the late 1970s. GPP was strongly correlated with water temperature in Biscayne Bay (r = 0.60) but had the strongest correlation with salinity in Tampa Bay (r = 0.39). These findings highlight the importance of more frequent production measurements in these complex estuaries, especially in the face of a changing climate.

The online version contains supplementary material available at 10.1007/s12237-025-01597-y.