[Effects on phosphorus fraction distribution in sediment by roots of Vallisneria natans].

The present study explored phosphorus fractions in sediments with the growth of Vallisneria natans. Sediment samples in different layers were collected at 20, 50 and 80 d, and vertical change of several phosphorus fractions were measured in the samples. The root distributions and biomass of the V. natans were measured. Our results showed that roots were distributed between 0 and 14 cm in the experimental device. The average number of roots and average root length were 58 and 5.86 cm. After 80 days growth, the percentage of V. natans root biomass were 45.99%, 32.75%, 16.03% and 5.23% in the sediment with depths of 0-3, 4-6, 7-10 and 11-14 cm. Total phosphorus (TP) content, phosphorus extracted by NaOH (NaOH-P), and organic phosphorus (OP) levels remarkably decreased (P < 0.05) in the area with a high concentration of tape grass roots. The content of phosphorus extracted by HCl (HCl-P), and inorganic phosphorus (IP), showed no significant difference (P > 0.05). The results suggest that V. natans root affects the migration and transformation of phosphorus species in the sediment.

[Distribution of nitrogen in the sediment of Taige south river estuary].

To characterize the distribution of nitrogen in the sediment of Taige south river estuary, column samples of sediments were collected and analyzed in April, 2012. Our results revealed that a synchronized trend existed among the levels of ammonium nitrogen (NH4(+) -N), organic nitrogen (Org-N) and total nitrogen (TN) in the surface layer of sediment. The NH4(+) -N positively correlated with TN and Org-N significantly (P < 0.05) while TN highly significantly correlated with Org-N (P < 0.01). Org-N was the major form of nitrogen, comprising 93.38% of total nitrogen (TN) averagely. Both horizontal and vertical distribution of nitrogen in sediments apparently changed along the distance to stream outlet. In the horizontal dimension in sediments, Org-N and TN decreased progressively as forwarding into the lake in the extending direction of the main stream, while showed a "W"-type fluctuation in the diverged direction away from the main stream. The level of NH4(+) -N decreased rapidly within 100 m to the stream outlet and remained constantly at a lower level beyond 100 m. However, the level of nitrate nitrogen (NO3(-) -N) stabilized within 0-800 m and increased greatly beyond 800 m. In the vertical dimension in sediments, the level of NH4(+) -N increased with increasing depth. As the distance to the stream outlet increasing, the enrichment of NO3(-) -N was enhanced in surface layers rather than in lower subsurface layers. Alternatively, the enrichment of Org-N and TN were reduced in surface layers but enhanced in subsurface layers.