Benthic nutrient flux in a shallow coastal environment

Area of Science:

• Marine ecology
• Biogeochemistry
• Sediment nutrient cycling

Background:

• Benthic environments play a crucial role in nutrient cycling within marine ecosystems.
• Understanding nutrient fluxes, particularly ammonia and nitrate, is vital for assessing marine productivity.
• Macrofaunal and microbial communities significantly influence sediment-water nutrient exchange.

Purpose of the Study:

• To quantify ammonia and nitrate efflux from fine sand sediments in Carmarthen Bay.
• To investigate the relationship between sediment nutrient efflux and the biomass of macrofauna and bacteria.
• To estimate the contribution of benthic ammonia flux to the nitrogen demand of phytoplankton.

Main Methods:

• Incubation of undisturbed sediment cores onboard ship.
• Determination of macrofaunal biomass, bacterial biomass, and sediment organic content.
• Measurement of oxygen consumption and application of multiple linear regression analysis.

Main Results:

• Ammonia efflux was significantly correlated with the biomass of polychaetes, molluscs, and other macrofauna.
• Bacterial biomass did not significantly improve the regression models for ammonia flux.
• Estimated annual ammonia efflux was 778 mmol N m^-2, meeting 44% of phytoplankton nitrogen demand.
• Nitrate efflux was lower than ammonia efflux, peaking in autumn.
• No significant relationship was observed between oxygen consumption and faunal or bacterial biomass.

Conclusions:

• Macrofauna are key drivers of ammonia efflux from these fine sand sediments.
• Benthic ammonia flux is a substantial but not sole source of nitrogen for phytoplankton, with seasonal limitations.
• Sediment nutrient dynamics are complex, with distinct contributions from ammonia and nitrate efflux.