| A headstream of multistage dam was chosen for the object in suburban Hefei. The solution of nutrient （NH4Cl and KH2PO4） and a conservative tracer （NaCl） were used to conduct tracer addition experiments. Based on the data sets of tracer experiments, OTIS model and nutrient spiraling theory were set to characterize the transient storage and quantitative estimate the nitrogen and phosphorus retention capacity. Poplar leaf litter was selected to assess the attenuation ability of organic matter in the study area, which employed leaf litter breakdown rate as evaluation index. Furthermore, in order to provide a basis for reduce and regulate of biogenic element （such as nitrogen and phosphorus, carbon）, nitrification rate of sediment was measured to investigated nutrient retention capacity and analysis the restricting effect of oxygen to nitrification. The main results were summed up as follows:（1） The hydrological parameters and transient storage of index changing with hydrological conditions show certain differences. Hydraulic diffusivity （D） was 0.001 to 0.260, exchange coefficient （α） was in the order of 10"4 to 10"3. Hydraulic retention factor Rh, was 2.068 to 7.013 s m-1, the average value was 4.268 s m-1. Fmed 200 was 5.53% to 34.15%, and the average value was 16.40%.（2） In main flow region, the attenuation coefficient of NH4% and SRP were between the order of 10"6 to 10"3, while the order of magnitudes reached 10-5 to 10"2 during transient storage and most order were negative. The value of nutrient spiraling metrics Vf NH4 and Vf-SRP was between the order of 10"6 to 10"3, the value of U-NH4+ and U-SRP between the order of 10-3 to 10-1, there are large difference between the uptake lengths of NH4 and SRP. That the nutrient uptakes lengths appear negative value in some headstream imply that the headstream acting as source of N or P, which means nutrient is in the released state.（3） The average breakdown rate of leaf litter at the primary tributary of Ershibu River was 0.00329 d-1,0.00741 d-1 and 0.01823 d-1 were respectively for tributary and pond, which basically agree with the variation tendency of physical and chemical characters. According the Gessner’s model, all sampling points of primary tributary had an ecosystem health score 0, only three points had the score 1 of secondary tributary; with respect to pond, the ecosystem health had a score 2, indicating that the health status of Ershibu river reaches were severely damaged.（4） PNR in Ershibu River ranged from 0.022 μmol·h-1·g-1 to 0.268 μmol·h-1·g-1,the median value was 0.124μmol·h-1·g-1, shows a higher levels than most reported values. However, the variation of ANR was 0.022 μmol·h-1·g-1 to 0.268 μmol·h-1·g-1, the median value was 142 μmol·h-1·m-2, which means the ANR in Ershibu River at low level. The distinction between ANR and PNR level indicated that the potential nitrification capacity of Ershibu River sediment could not be released effectively, which was caused by the low oxygen content in the river. Consequently, enhancing the ability of oxygen reaeration and increasing dissolved oxygen content are the basic measures to control the ammonia pollution in Ershibu River. |
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