[Effects of Source Depletion on Vapor Intrusion Risk Assessment].

The current regulatory site investigation employs the J&E model to predict vapor intrusion risk. However, the J&E model assumes that the source concentration is constant for a given exposure period, which is not consistent with the actual site source under depletion. In this study, we compared the differences between the J&E model (constant source), SD source depletion model, and RBCA source depletion model for predicting indoor concentration variation as well as the risk levels during the exposure period with a case study in Beijing. The results showed that the source and indoor air concentrations predicted by the SD and RBCA models showed exponential decreases, whereas those predicted by the J&E model maintained high concentrations throughout the exposure period, which greatly overestimated the risk. The RBCA predicted source depletion at the fastest rate, but the predicted indoor air concentrations were still lower than those of the SD model, which was related to the fact that the RBCA did not consider the effect of buildings on source depletion and did not follow mass conservation. Further, the sensitivity analysis showed that the pressure difference (dP) had the greatest influence on the source concentration in the SD model. For the calculated carcinogenic risk and hazard quotients, the J&E constant source model, the SD source depletion model, and the RBCA source depletion model were ranked in descending order. The results indicated that in general the J&E model was too conservative, the RBCA model may have underestimated risk, and the SD model was more suitable for quantifying vapor intrusion risk in reality.

Species richness disparity in tropical terrestrial herbaceous floras: Evolutionary insight from Collabieae (Orchidaceae).

Species richness is spatially heterogeneous even in the hyperdiverse tropical floras. The main cause of uneven species richness among the four tropical regions are hot debated. To date, higher net diversification rates and/or longer colonization time have been usually proposed to contribute to this pattern. However, there are few studies to clarify the species richness patterns in tropical terrestrial floras. The terrestrial tribe Collabieae (Orchidaceae) unevenly distributes in the tropical regions with a diverse and endemic center in Asia. Twenty-one genera 127 species of Collabieae and 26 DNA regions were used to reconstruct the phylogeny and infer the biogeographical processes. We compared the topologies, diversification rates and niche evolutionary rates of Collabieae and regional lineages on empirical samplings and different simulated samplings fractions respectively. Our results suggested that the Collabieae originated in Asia at the earliest Oligocene, and then independently spread to Africa, Central America, and Oceania since the Miocene via long-distance dispersal. These results based on empirical data and simulated data were similar. BAMM, GeoSSE and niche analyses inferred that the Asian lineages had higher net diversification and niche evolutionary rates than those of Oceanian and African lineages on the empirical and simulated analyses. Precipitation is the most important factor for Collabieae, and the Asian lineage has experienced more stable and humid climate, which may promote the higher net diversification rate. Besides, the longer colonization time may also be associated with the Asian lineages' diversity. These findings provided a better understanding of the regional diversity heterogeneity in tropical terrestrial herbaceous floras.

[Landscape pattern change and its simulation forecast in Zigui County of Three Gorges Reservoir Area].

Based on the TM images of 1987 and 2002, the landscape pattern change of Zigui County from 1987 to 2002 was analyzed by using landscape index method; and the simulation forecast of this change in next 50 years was conducted by using Markov model. The results showed that in 1987-2002, the landscape pattern of Zigui County changed dramatically. The area of sparse wood land increased greatly while that of upland and shrub land decreased obviously, and the distribution of the areas of different landscape types tended to balance. The average shape index of landscape had an overall decline, which was represented by the concentrated and connected distribution of different landscape types, simplification of landscape shape, and obvious human interference. As a whole, the landscape diversity and fragmentation in Zigui County were improved to some extent. In next 50 years, the area of sparse wood land in Zigui would have a rapid increase, followed by that of forestland, while the areas of upland and shrub land would be declining, and the other landscape types would have a less fluctuation in their areas. The main driving forces of the landscape pattern change in Zigui were the relocation of the County and the implementation of forestry policies.