Seasonal organic mineralisation and denitrification in intertidal sediments and their relationship to the abundance of Enteromorpha sp. and Ulva sp

Sedimentary organic matter mineralisation (oxygen uptake), nitrogen (N) loss (denitrification) and nutrient exchange were measured seasonally in areas of both high and low Enteromorpha sp. and Ulva sp. cover at 6 sites in 2 harbours on the south coast of England. Measurements of macroalgal and phytoplankton photosynthesis were also carried out. Sedimentary carbon (C) and N cycling was most rapid at the sites with a heavy cover of macroalgae. Macroalgae were responsible, on average, for 57% of total dark oxygen uptake, with sediment bacterial respiration accounting for the remaining 43%. Dark rates of nutrient uptake for Enteromorpha sp. and Ulva sp. were equivalent to 70% of those in the light. Denitrification rates were low (D sub(w) [NO sub(3) super(-) from overlying water]