[Soil available nitrogen and phosphorus contents and the environmental impact factors across different land use types in typical karst rocky desertification area, Southwest China.] / å–€æ–¯ç‰¹çŸ³æ¼ åŒ–åœ°åŒºä¸åŒåœŸåœ°åˆ©ç”¨ç±»åž‹åœŸå£¤æ°®ç£·æœ‰æ•ˆæ€§åŠå ¶çŽ¯å¢ƒå½±å“å› å­.

In this study, we collected soil samples from four different land use types (forest land, shrub land, grassland and abandoned land) in Huajiang valley of Guizhou Province, a typical karst rocky desertification area in Southwest China. Correlation analysis and redundancy analysis were used to examine the distribution of available nitrogen (N) and available phosphorus (P) in diffe-rent soil layers from 0 to 30 cm and the relationships between soil environmental factors (soil physical indexes, organic carbon components, electrochemical properties, metal oxides and enzyme activities) and the contents of available N and available P. The results showed that the concentrations of soil total N, total P, available N, available P decreased significantly with the increases of soil depth. The concentrations of soil available N and available P in forest land and shrub land were significantly higher than those in grassland and abandoned land, which were significantly positively correlated with soil organic carbon composition, enzyme activity, surface electrochemical properties and amorphous mental oxide while significantly negatively correlated with soil silt and free metal oxides. Results of the redundancy analysis showed that the environmental factors affecting soil availa-ble N and available P of the four land use types were basically the same, with soil particulate organic carbon, total organic carbon and soil specific surface area playing a key role in driving the variations of soil available N and available P. The efficient explanation of variation to soil available N and P contents by soil particulate organic carbon might be due to the reduction of soil nutrient loss by the storage of N and P in organic matter. Except for high enzyme activity and electrochemical properties of forest land and shrub land, the higher soil available N and available P concentrations compared with grassland and abandoned land might be resulted from the inhibition of free iron and aluminum oxides information by higher soil organic carbon content and the reduced adsorption and fixation of N and P by iron and aluminum oxides.

[Carbon, nitrogen, and phosphorus budgets of bottom-cultured clam Ruditapes philippinarum].

In order to elucidate the role of bottom-cultured clams in the coastal nutrient cycle, the seasonal filtration, ingestion and biodeposition rates were in situ measured and carbon (C), nitrogen (N) and phosphorus (P) budgets of Ruditapes philippinarum among four seasons were modeled. The results showed that the scope for growth of R. philippinarum in carbon (SFG(C)), nitrogen (SFG(N)), and phosphorus (SFG(P)) all varied significantly among seasons, with the highest values in spring. Meanwhile, SFG(C) was negative in summer, SFG(N) and SFG(P) were always positive throughout the year. The seasonal variations of SFG(C), SFG(N) and SFG(P) were -3.94-49.82 mg C x ind(-1) x d(-1), 0.72-9.49 mg N x ind(-1) x d(-1), and 0.15-3.06 mg P x ind(-1) x d(-1), respectively. The net growth efficiencies in carbon (K(C2)), nitrogen (K(N2)), and phosphorus (K(P2)) also showed a distinct seasonal pattern among seasons, and ranked as K(P2) > K(N2) > K(C2). The C, N, and P budgets illustrated that the R. philippinarum population relatively used more N and P than C for growth and efficiently transferred the pelagic primary production to a higher trophic level. The current study suggested that R. philippinarum bottom-cultured at large scale might play a dominant role in the nutrient cycle of the coastal ecosystem and should be considered as an important ecological component in coastal areas.

[Self-pollution in Ruditapes philippinarum bottom-cultured area of Zhuanghe coast].

By using sediment trap and closed respirator, a year-round in situ investigation was made on the bio-deposition rate, ammonia excretion rate, and phosphate excretion rate in the Ruditapes philippinarum bottom-cultured area of Zhuanghe coast. The three test rates of R. philippinarum all showed obvious seasonal variability, with the bio-deposition rate ranged in 0.15-1.47 g x ind(-1) x d(-1) (annual average 0.61 g x ind(-1) x d(-1)), ammonia excretion rate ranged in 0.02-0.40 mg x ind(-1) x d(-1) (annual average 0.17 mg x ind(-1) x d(-1)), and phosphate excretion rate ranged in 0.01-0.39 mg x ind(-1) x d(-1)(annual average 0. 13 mg x ind(-1) x d(-1)). Based on these, it was estimated that the annual bio-deposit production by the bottom-cultured R. philippinarum in Zhuanghe coast could reach as high as 5.46 x 10(7) t dry mass, amounting to 9.07 x 10(6) t organic matter (OM), 1.00 x 10(6) t organic carbon (OC), or 1.18 x 10(5) t organic nitrogen (ON), and the annual NH4+ -N and PO4(3-)-P productions were 1.49 x 10(4) t and 1.15 x 10(4) t, respectively. Our results suggested that for the large scale and high density bivalve culture in China coasts, the potential impacts of self-pollutants by filter-feeding bivalves on the environment should not be neglected.