Rapid Losses of Surface Elevation following Tree Girdling and Cutting in Tropical Mangroves.

Discussion Conclusions Materials and Methods Acknowledgments Author Contributions References Reader Comments (0) Figures Abstract The importance of mangrove forests in carbon sequestration and coastal protection has been widely acknowledged. Large-scale damage of these forests, caused by hurricanes or clear felling, can enhance vulnerability to erosion, subsidence and rapid carbon losses. However, it is unclear how small-scale logging might impact on mangrove functions and services. We experimentally investigated the impact of small-scale tree removal on surface elevation and carbon dynamics in a mangrove forest at Gazi bay, Kenya. The trees in five plots of a Rhizophora mucronata (Lam.) forest were first girdled and then cut. Another set of five plots at the same site served as controls. Treatment induced significant, rapid subsidence (−32.1±8.4 mm yr−1 compared with surface elevation changes of +4.2±1.4 mm yr−1 in controls). Subsidence in treated plots was likely due to collapse and decomposition of dying roots and sediment compaction as evidenced from increased sediment bulk density. Sediment effluxes of CO2 and CH4 increased significantly, especially their heterotrophic component, suggesting enhanced organic matter decomposition. Estimates of total excess fluxes from treated compared with control plots were 25.3±7.4 tCO2 ha−1 yr−1 (using surface carbon efflux) and 35.6±76.9 tCO2 ha−1 yr−1 (using surface elevation losses and sediment properties). Whilst such losses might not be permanent (provided cut areas recover), observed rapid subsidence and enhanced decomposition of soil sediment organic matter caused by small-scale harvesting offers important lessons for mangrove management. In particular mangrove managers need to carefully consider the trade-offs between extracting mangrove wood and losing other mangrove services, particularly shoreline stabilization, coastal protection and carbon storage.

The total margin of exposure of ethanol and acetaldehyde for heavy drinkers consuming cider or vodka

Heavy drinkers in Scotland may consume 1600 g ethanol per week. Due to its low price, cider may be preferred over other beverages. Anecdotal evidence has linked cider to specific health hazards beyond other alcoholic beverages. To examine this hypothesis, nine apple and pear cider samples were chemically analysed for constituents and contaminants. None of the products exceeded regulatory or toxicological thresholds, but the regular occurrence of acetaldehyde in cider was detected. To provide a quantitative risk assessment, two collectives of exclusive drinkers of cider and vodka were compared and the intake of acetaldehyde was estimated using probabilistic MonteeCarlo type analysis. The cider consumers were found to ingest more than 200-times the amount of acetaldehyde consumed by vodka consumers. The margins of exposure (MOE) of acetaldehyde were 224 for the cider and over 220,000 for vodka consumers. However, if the effects of ethanol were considered in a cumulative assessment of the combined MOE, the effect of acetaldehyde was minor and the combined MOE for both groups was 0.3. We suggest that alcohol policy priority should be given on reducing ethanol intake by measures such as minimum pricing, rather than to focus on acetaldehyde.