Characteristics of 210Po in Asian overbite clam (Potamocorbula laevis) from the coastal area at Thai Binh province, Vietnam.

210Po concentration in the edible muscle tissue and digestive diverticulum organs of Asian overbite clam at the near-shore Thai Binh, Vietnam was analyzed using alpha detectors. The 210Po activity in muscle tissue and digestive diverticulum organs ranged from 5 ± 1 to 178 ± 10 and from 118 ± 7 to 812 ± 12 Bq.kg-1 with the average value of 25 and 324 Bq.kg-1, respectively. Results showed that 210Po activity in the digestive diverticulum was significantly higher than in the muscle tissue. There was a slightly inverse correlation between 210Po activity in muscle tissue, digestive diverticulum, and clam weight and size. The annual committed effective dose was calculated from 210Po due to the consumption of Asian overbite clam for adults in the study area was higher than the guideline value of 0.2 - 1 mSv.y-1.

Fine root production in a chronosequence of mature reforested mangroves.

Mangroves are among the world's most carbon-dense ecosystems, but have suffered extensive deforestation, prompting reforestation projects. The effects of mangrove reforestation on belowground carbon dynamics are poorly understood. In particular, we do not know how fine root production develops following mangrove reforestation, despite fine root production being a major carbon sink and an important control of mangrove soil accretion. Using minirhizotrons, we investigated fine root production and its depth variation along a chronosequence of mature Vietnamese mangroves. Our results showed that fine root production decreases strongly with stand age in the uppermost 32 cm of our soil profiles. In younger mangrove stands, fine root production declines with depth, possibly due to a vertical gradient in soil nutrient availability; while root production in the oldest stand is low at all depths and exhibits no clear vertical pattern. A major fraction of fine root production occurs deeper than 30 cm, depths that are commonly omitted from calculations of mangrove carbon budgets. Younger mangroves may accrue shallow soil organic matter faster than older mangroves. Therefore, root productivity and forest stand age should be accounted for when forecasting mangrove carbon budgets and resistance to sea-level rise.

Distribution and annual committed effective dose assessment of 210Po in popular marine species at the near-shore Binh Thuan province, Vietnam.

210Po concentration in thirty popular marine species (twenty five fishes, four bivalves and one crab) with different habitats, feeding types, and trophic levels at the near-shore Binh Thuan, Vietnam was analyzed using the alpha detectors. The 210Po activities were widely ranged from 3.07 ± 0.18 in a fish species (Bumpnose trevally) to 78.6 ± 5.3 Bq/kg w.w in a bivalve species (Green mussel) with the average value of 16.6 Bq/kg w.w. The results showed that the species with lower trophic level value have higher 210Po concentration. Regarding the feeding types, the 210Po concentration in the omnivorous species is about 2.9 times higher than in the carnivorous species. The species living in demersal zone accumulated a high 210Po in comparison with species living in reef-associated and pelagic-neritic zones. The calculated annual committed effective dose from 210Po due to the ingestion of seafood from demersal zone and bivalve species of the area was significant high.

Sensitivity of mangrove soil organic matter decay to warming and sea level change.

Mangroves are among the world's most carbon-dense ecosystems, but they are threatened by rapid climate change and rising sea levels. The accumulation and decomposition of soil organic matter (SOM) are closely tied to mangroves' carbon sink functions and resistance to rising sea levels. However, few studies have investigated the response of mangrove SOM dynamics to likely future environmental conditions. We quantified how mangrove SOM decay is affected by predicted global warming (+4°C), sea level changes (simulated by altering of the inundation duration to 0, 2, and 6 hr/day), and their interaction. Whilst changes in inundation duration between 2 and 6 hr/day did not affect SOM decay, the treatment without inundation led to a 60% increase. A warming of 4°C caused SOM decay to increase by 21%, but longer inundation moderated this temperature-driven increase. Our results indicate that (a) sea level rise is unlikely to decrease the SOM decay rate, suggesting that previous mangrove elevation gain, which has allowed mangroves to persist in areas of sea level rise, might result from changes in root production and/or mineral sedimentation; (b) sea level fall events, predicted to double in frequency and area, will cause periods of intensified SOM decay; (c) changing tidal regimes in mangroves due to sea level rise might attenuate increases in SOM decay caused by global warming. Our results have important implications for forecasting mangrove carbon dynamics and the persistence of mangroves and other coastal wetlands under future scenarios of climate change.