2:40 PM - 2:55 PM
[ACG38-04] Evaluation of nutrient absorption and release characteristics of seagrass beds in subtropical waters
Global warming and various local anthropogenic pollutions have been reported to have caused the decline of coral communities in tropical and subtropical regions. On the other hand, on the landward side of the coral reef, seagrass beds and mangrove forests absorb high concentrations nutrients, trap suspended solids, and release decomposed organic matter as nutrients again. These functions of seagrass beds are expected to reduce pollution load to coral communities spreading offshore and provide a favorable environment, but quantitative knowledge is lacking. This study aims to evaluate the time-varying nutrient fluxes at the sediment-water interface in the seagrass bed in response to nutrient loading due to submerged groundwater discharge.
Chamber experiments were conducted at Bise Coral reef, Okinawa, in July 2023 and Nagura Bay, Ishigaki Island, in September. Two dominant seagrass species, Thalassia hemprichii and Cymodocea serrulata, were incubated in light and dark conditions in a closed system. After adding nutrients at concentrations that assumed groundwater discharge, water samples for the analyses of nutrients, DIC, and DO concentrations were collected four times (i.e., t=0, 15, 30, and 60 min). Bottle incubation experiments were also conducted in laboratory tanks to measure nutrient fluxes from seagrass leaves only.
Chamber experiments showed that the nutrient uptake tended to decrease with time and that nutrients were uptaken more under light conditions than under dark conditions. Factors contributing to variation in nutrient flux will be discussed in terms of nutrient concentration, light intensity, seagrass leaf area in the chamber, and leaching from the sediment.
Chamber experiments were conducted at Bise Coral reef, Okinawa, in July 2023 and Nagura Bay, Ishigaki Island, in September. Two dominant seagrass species, Thalassia hemprichii and Cymodocea serrulata, were incubated in light and dark conditions in a closed system. After adding nutrients at concentrations that assumed groundwater discharge, water samples for the analyses of nutrients, DIC, and DO concentrations were collected four times (i.e., t=0, 15, 30, and 60 min). Bottle incubation experiments were also conducted in laboratory tanks to measure nutrient fluxes from seagrass leaves only.
Chamber experiments showed that the nutrient uptake tended to decrease with time and that nutrients were uptaken more under light conditions than under dark conditions. Factors contributing to variation in nutrient flux will be discussed in terms of nutrient concentration, light intensity, seagrass leaf area in the chamber, and leaching from the sediment.