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The paradigm for understanding the accumulation of organic carbon in vegetated coastal "blue carbon" habitats holds that burial of organic carbon (Corg) slows decomposition and leads to stability of carbon stocks. Further, it is generally assumed that the presence of the plant communities contributes to the buried organic matter and the stability of the carbon stocks. In this study, these assumptions were tested and the lability of soil organic carbon was examined as a function of environmental and plant community drivers. Samples of surficial sediment and seagrass community characteristics were collected at 93 locations across the ca. 15,000 km2 of seagrass beds in south Florida. Ramped pyrolysis was used to describe the relative lability of soil organic carbon across the landscape. Organic matter (OM) was lost at all temperatures from 180 to 600 °C, suggesting that even the relatively high combustion temperature of 550 °C underestimates OM content by ≈ 10% on average. Additionally, deployments of model substrates (canvas strips) were used to examine decomposition rates of buried and surficial organic material at a subset of these sites. On average, finer, muddier soils contained slightly higher Corg stocks than coarser sediment sites, but the relationships between sediment grain size and seagrass community structure was weak. The lability of soil organic carbon varied with sediment grain size; as much as 80% of the Corg was refractory in coarse-grained soils compared with less than 30% in muddy soils. In muddy soils, burial decreased cellulose decomposition rate by an average of 22–39% compared with surficial breakdown, but in coarse-grained soils, burial enhanced cellulose decomposition rate by at least 55%. Taken as a whole, this study suggests that burial does not enhance Corg storage in all blue carbon environments, and that soil C stores are only weakly correlated with seagrass biomass at the landscape scale. [ABSTRACT FROM AUTHOR]

Variation and uncertainty in estimated evaporation was determined over time and between two locations in Florida Bay, a subtropical estuary. Meteorological data were collected from September 2001 to August 2002 at Rabbit Key and Butternut Key within the Bay. Evaporation was estimated using both vapor flux and energy budget methods. The results were placed into a long-term context using 33 years of temperature and rainfall data collected in south Florida. Evaporation also was estimated from this long-term data using an empirical formula relating evaporation to clear sky solar radiation and air temperature. Evaporation estimates for the 12-mo period ranged from 144 to 175 cm yr-1, depending on location and method, with an average of 163 cm yr-1 (± 9%). Monthly values ranged from 9.2 to 18.5 cm, with the highest value observed in May, corresponding with the maximum in measured net radiation. Uncertainty estimates derived from measurement errors in the data were as much as 10%, and were large enough to obscure differences in evaporation between the two sites. Differences among all estimates for any month indicate the overall uncertainty in monthly evaporation, and ranged from 9% to 26%. Over a 33-yr period (1970-2002), estimated annual evaporation from Florida Bay ranged from 148 to 181 cm with an average of 166 cm yr-1. Rainfall was consistently lower in Florida Bay than evaporation, with a long-term average of 106 cm yr-1. Rainfall considered alone was uncorrelated with evaporation at both monthly and annual time scales; when the seasonal variation in clear sky radiation was also taken into account both net radiation and evaporation were significantly suppressed in months with high rainfall. [ABSTRACT FROM AUTHOR]