In situ production and respiration of the benthic community during emersion on subtropical intertidal sandflats

In situ benthic community production and respiration during emersion were measured monthly in the course of a 19 mo survey from June 2008 to December 2009 by monitoring CO2 fluxes in benthic chambers on intertidal sandflats of a subtropical coastal wetland. Maximum gross community production (GCP(m)) and community respiration (CR) all exhibited higher values in summer and fall and lower values in spring and winter. GCP(m) and CR were positively correlated with air temperature. Temperature coefficients (Q(10)) showed that a rise of 10 degrees C would increase the GCP(m) and CR by factors of 3.72 and 4.80, respectively. GCP(m) was also positively correlated with sediment grain size and negatively correlated with the silt/clay content. CR exhibited a strong positive correlation with sediment chlorophyll a concentration and macrofaunal biomass. To provide an accurate annual budget of benthic production during emersion, corrections were considered for cloudiness and the time lag between emersion and maximum production due to vertical migration of benthic diatoms and variations in CR during nighttime emersion periods. Annual net community production (NCP) during emersion on sandflats was estimated to be 2.87 g C m(-2) yr(-1), indicating an autotrophic system. However, taking into account the variation in benthic metabolism during immersion, the subtropical intertidal sandflats shifted to a heterotrophic system, and annual NCP was calculated to be -91.47 g C m(-2) yr(-1).