Abstract
Anthropogenic influence on the environment has increased carbon dioxide (CO2) in the atmosphere, and consequently in the ocean. The ocean is the largest carbon sink, sequestering one-third of carbon in the atmosphere. An increase in CO2 levels in the ocean reduces the pH of the seawater, causing ocean acidification. It is important to understand and conserve ecosystems that sequester large amounts of carbon, known as carbon sinks, in conjunction with reducing emissions. Mangrove forests are observed to have a disproportionally important role in sequestering carbon.
The purpose of this study was to observe how shallow mangrove lagoons in the lower Florida Keys change the composition of CO2 in surrounding seawater. Dissolved inorganic carbon (DIC) and total alkalinity (TA) can be used along with temperature and salinity to determine the pH and partial pressure of CO2 (pCO2) in the water. In this study, both DIC and TA of the seawater in a shallow mangrove lagoon were used to find how the levels of pH and pCO2 changed, within the lagoon, in a 24-hour sampling period. The study site was in Summerland Key at a shallow mangrove lagoon. Four sample sites were selected across the mouth of the lagoon to sample the water chemistry entering and exiting the lagoon. Three control sites were selected in the adjacent channel. Water samples were collected every three hours over a 24-hour period. Temperature, salinity, dissolved oxygen (DO), and time of collection were recorded for each water sample at the mouth of the lagoon. DO, seawater temperature, and salinity were measured along three transects within the lagoon. Water samples were also collected at peak light and dark hours. A benthic survey was conducted within the lagoon.
The results indicate the mangrove lagoon acts as a source of CO2. The results show organisms are adding both DIC and TA to the seawater, which can be explained by respiration and dissolution of sediments. The mangrove lagoon was acting as a source of pCO2 rather than a carbon sink, higher rates of respiration and slightly lower rates of dissolution are occurring.