[Spatial variations of biogenic elements in coastal wetland sediments of the Jiulong River Estuary].

To reveal the spatial distribution of biogenic elements and their influencing factors in the typical subtropical coastal wetland, both surface and core sediment samples were collected from the Jiulong River Estuary, southeast China in summer 2009. The biogenic elements including carbon, nitrogen, phosphorus, sulfur (C, N, P, S) were determined by Element Analyzer and Flow Injection Analyzer. The concentrations of TC, TN, TP, and TS were (12.64 +/- 2.66) g x kg(-1), (1.57 +/- 0.29) g x kg(-1), (0.48 +/- 0.06) g x kg(-1), and (2.61 +/- 1.37) g x kg(-1), respectively. Further, these biogenic elements showed a distinct spatial pattern which closely related with the vegetation type and tide level. Values of TC, TN, TP in the surface sediment of mangrove vegetation zones were higher than those in the cord-grass and mudflat zones, while TC, TN, TP concentrations in the high tide level regions were higher than those in the middle and low tide level regions. The TS concentration was the highest in cord-grass vegetation and middle tidal level zones. The TC and TN values in sedimentary core decreased gradually with depth, and they were the highest in the mangrove sites, followed by cord-grass and mudflat sites at the same depth. In mudflat sedimentary core, the average content of TP was the lowest, whereas TS was the highest. Redundancy analysis revealed that vegetation type, pH and tide level were the main factors influencing the distribution of biogenic elements in surface sediments of the Jiulong River Estuary, by explaining 24.0%, 19.0% and 11.6% of total variation in the four biogenic elements (C, N, P and S), respectively.

[Morphometric analysis of six natural populations of Difflugia tuberspinifera].

The morphometrical variability of six natural populations of Difflugia tuberspinifera was investigated using the statistic methods based on 374 samples from Yangtze River and Pearl River valleys. The size frequency distribution analysis indicated that D. tuberspinifera is a size-monomorphic species with normal distribution of shell height, shell diameter and aperture diameter. The size of spine length, collar height, foreside length and number of conical spines are the most variable. The correlation analysis showed that most characters are inter-correlated with P<0.05. The shell height, shell diameter, aperture diameter, spine length, collar height, rear end length, foreside length, number of aperture tooth-like structures and number of conical spines differed significantly between different populations (P<0.0001), but principal component analysis (PCA) did not clearly distinguish the six populations based on the morphometric data. However, the cluster analysis separated the six populations into two groups, the Pearl River-Yangtze River group and the Yangtze River group. Further, the populations with different shell characters can coexist within the same river valley. Thus, there is a high morphological variability or diversity within the populations of D. tuberspinifera which is related with local environmental conditions.