Carbonate chemistry seasonality in a tropical mangrove lagoon in La Parguera, Puerto Rico.

Erick M García-Troche,Joseph E Salisbury,Julio M Morell,Melissa Meléndez,Kay C Vopel

doi:10.1371/journal.pone.0250069

Abstract

We investigated the seasonal carbonate chemistry variability within a semi-enclosed tropical mangrove lagoon in southwestern Puerto Rico. Biweekly measurements of seawater temperature, salinity, total alkalinity (TA), and dissolved inorganic carbon (DIC) were conducted from 2014 to 2018. We describe the possible mechanisms driving the observed variability by correlating the DIC/TA ratio with pH and Ωarg, suggesting that the mean pH (7.87 ± 0.09) and aragonite saturation state (Ωarg, 2.96 ± 0.47) of the mangrove lagoon negatively affected calcification. The measured pCO2 and DIC/TA ratios indicate that heterotrophic activity was the primary driver for persistent acidification, which reached its maximum expression during the wet season. We conclude that mangrove lagoons with limited seawater exchange and high carbon input will not mitigate ocean acidification.

Highlights

There is an increasing research interest to identify ecosystems where vulnerable species could persist under foreseen future scenarios, including high atmospheric carbon dioxide (CO2) concentrations and seawater temperatures [1]
Differences in salinity and temperature variabilities between BB and SE support the contention of limited exchange between BB and outer coastal waters [27, 53]
The salinity decrease at SE after April was due to the influence of riverine water from the Amazon and Orinoco river plumes, later magnified by the maximum outflow of the Orinoco in September [29, 30] and the start of the wet season in August (Fig 3B)

Summary

Introduction

There is an increasing research interest to identify ecosystems where vulnerable species could persist under foreseen future scenarios, including high atmospheric carbon dioxide (CO2) concentrations and seawater temperatures [1]. Studies suggest that different coastal ecosystems, such as seagrass beds [6] and mangroves [7, 8], can mitigate ocean acidification (OA) driven by oceanic uptake of anthropogenic CO2. A buffering effect may occur when “alkalinity increases the CO2 uptake capacity of seawater by neutralizing H+ ions and buffering the pH change associated with CO2 inputs” [9]. Seagrass ecosystems buffer OA at shallow depths and reduced water mass turnover [10, 11] by raising the pH and calcium carbonate (CaCO3) saturation while they are in a state of net autotrophy [10]. The buffering effect may be limited to specific periods throughout the year [12] and could have the opposite effect by exacerbating OA in the future [13]

Methods

Results

Conclusion