三峡支流消落带表层沉积物氮矿化动力学参数估算

为揭示干湿循环过程对消落带沉积物氮矿化动力学特征的影响,以三峡典型支流——澎溪河为例,分别于上、下游两个水文断面采集170 m(高)和150 m(低)水位高程消落带的表层(0~15 cm)沉积物样品。采用厌氧培养法测定其净氮矿化速率,应用One-pool、Two-pool、Special和有效积温(EATM)四种模型拟合氮矿化过程并建立估算方程。结果表明,沉积物总碳、总氮、碳氮比、有机质、粘粒、粉粒和铵态氮含量随高程降低而增加,而沉积物总磷、砂砾、硝态氮趋势相反(P0.05)。低、高水位高程氮矿化最优拟合模型分别为One-pool和Special,其中易矿化速率常数(kd)分别为0.17、0.12 d-1,易矿化势(fd)分别为4.05%和4.71%。另外,fd与总碳、总氮、碳氮比、有机质、铵态氮、粉粒呈显著负相关,与硝态氮和砂砾呈显著正相关(P0.05),而kd相反,且两参数可用有机质和碳氮比进行估算。

Parameter estimates of sediment nitrogen mineralization kinetics in the water level fluctuation zone of a Three Gorges Reservoir tributary

To reveal the effect of drought-rewetting process on the nitrogen mineralization kinetics in the sediment of the water level fluctuation(WLF) zone, surface sediment samples were collected over various water level altitudes at the upper and downstream sections of the Pengxi River. The sediment nitrogen mineralization rate was evaluated with anaerobic incubation. The one-pool, two-pool, special, and effective accumulated temperature models(EATM) were applied to fit the data of nitrogen mineralization kinetics in sediments. The result showed that total organic carbon(C), total nitrogen(N), organic matter(OM), clay, silt, and NH₄⁺-N in the higher altitude were lower than that in the lower altitude, which is on the contrary to total phosphorus, sand, and NO₃^--N. The one-pool model and special model were the optimal models for fitting nitrogen mineralization in sediments at low and high altitudes, respectively. The N mineralization rate constants(k_d) were 0.17 d^-1 and 0.12 d^-1, while the N mineralization potentials(f_d) were 4.05% and 4.71% in the low and high altitude sediments, respectively. The f_d was negatively correlated with C, N, C/N ratio, OM, NH₄⁺-N, and silt, and was positively correlated with NO₃^--N and sand (P<0.05). The k_d value had an opposite trend compared to the variation in f_d. The model parameters of f_d and k_d were successfully estimated by using the OM and C/N ratio. The current study revealed that nitrogen mineralization kinetics in sediment had a strong correlation with the water nitrogen content, and could thus be used to predict the contribution of nitrogen input into the WLF zone as an indicator of river eutrophication.