[Characteristics of sediment phosphorus in the Jiulong River-Reservoir system and its ecological significance].

Sediment phosphorus (P) content and component ratio from 16 sites along the North Jiulong River-reservoir system were analyzed using the Standard Measurement and Test (SMT) procedure. The spatial pattern and characteristics of sediment P and its ecological significance in the Jiulong River-reservoir system were examined in combination with water measurement and watershed information. Total P content in sediments ranged from 387 to 2092 mg x kg(-1) with an average of 1032 mg x kg(-1). Inorganic phosphorus (IP) dominated P in sediment, accounting for 48%-98% of TP, and Fe/Al-bound phosphorus (Fe/Al-P) took 43%-99% of IP. The spatial pattern of sediment showed that TP and Fe/Al-P were higher in upstream and lower in downstream, corresponding to the spatial variation of surface water P and land-based loads from animal waste, human waste and fertilizer loss. Spatial variation of TP in sediment was controlled by Fe/AI-P along the North Jiulong River. The P-rich sediment with a great release potential due to the high ratio of Fe/ Al-P, the typical spatial pattern, and the lower N/P ratio observed in upstream water (where phytoplankton growth tends to be weakly limited by phosphorus), are likely to explain the fact that algal blooms first appear in the upstream and then spread to downstream reservoirs along the North Jiulong River. Present findings concerning sediment P characteristics indicate an important regulating effect and the ecological significance on the process of algal blooms in the Jiulong River.

[Preliminary results concerning summer-time denitrification in the Jiulong River Estuary].

Denitrification is an important process mitigating nitrogen (N) pollution in aquatic systems. Water samples in 13 sites throughout the Jiulong River Estuary were collected in July, 2010 in a preliminary investigation of the denitrification rate in this area. As end-products of denitrification, dissolved N2 was measured by determining N2 : Ar ratios using MIMS (HPR-40), while the concentration of nitrous oxide (N2O) dissolved in water was determined by Purge and Trap-Gas Chromatography. The results showed significant spatial variance of net increase of dissolved N2 (ranging between - 9.9 and 66.8 micromol x L(-1)) and N2O (ranging between 4.3 and 31.5 nmol x L(-1)) in the Jiulong River Estuary. The net increase of dissolved N2 and N2O declined gradually from river sites to sea sites. Dissolved N2O was supersaturated by 170%-562%. The air-water fluxes of N2 ranged between -2.9 and 53.2 mmol x (m2 x d) (-1), and N2O between 5.2 and 23.9 micromol x (m2 x d)(-1). The N2O yield shared only 0.03% - 1.2% (average 0.25%) of total N air-water flux. The results suggested that water temperature and nutrient (N and P) were the key factors influencing denitrification. The denitrification rate is controlled by nitrate level at fresh-water sites with salinity < 0.5%. However, in salty waters, net increase in N2 and N2O mainly originated from denitrification occurring upstream of the estuary, and was dominated by the salinity gradient due to tidal mixing.