基于OTIS模型的巢湖十五里河源头段氮磷滞留特征

为揭示巢湖十五里河源头河段氮磷营养盐滞留特征,选择NH4Cl、KH2PO4及NaCl作为示踪剂,开展野外现场示踪实验.根据获得的氯离子浓度和营养盐浓度穿透曲线数据信息,利用OTIS与OTIS-P计算软件,估算水文参数(D、A、As、a等)和营养盐一阶吸收系数(λ、λs).在此基础上,计算暂态存储指标和营养盐吸收相关参数值,定量评估主河道流动水体与暂态存储对NH4+和SRP的损失贡献.结果表明,主河道与暂态存储区NH4+吸收系数平均值分别为3.88×10-6,8.81×10-4s-1,SRP分别为7.80×10-6,7.98×10-8s-1;综合衰减系数k-NH4平均值为1.64×10-4s-1,k-SRP为7.80×10-6s-1;NH4+和SRP的吸收长度Sw-NH4、Sw-SRP相当大,分别为1632.88,25471.32m,意味着该河段经由物理或生态过程去除N、P的可能性低;该河段Vf-NH4、Vf-SRP 值较营养盐浓度低的溪流或小河流偏小,但U-NH4、U-SRP则明显偏大;暂态存储对于NH4+损失的平均贡献率为93.82%,主河道水流对SRP损失的平均贡献率高达99.70%.

Characteristics of nitrogen and phosphate retention in the headwater stream of Shiwulihe in Lake Chaohu basin based on OTIS model

To investigate the basic characteristics of nitrogen and phosphate nutrient retention in the headwater stream of Shiwulihe, Lake Chaohu basin, a solution containing NH4Cl or KH2PO4 addition and a conservative tracer (NaCl) was used to conduct field experiments by slug injection. According to the data sets of breakthrough curves of chloride and nutrient concentration, the OTIS model code and OTIS-P software, proposed by Runkel (United States Geological Survey, USGS), were employed to estimate hydrological parameters (e.g. D, A, As, a) and first-order uptake rate coefficients (i.e. λ and λs). And on this basis the reach-scale transient storage metrics and nutrient uptake parameters were calculated as well as the fraction of uptake contribute to and SRP between the main channel and transient storage zone was estimated. Study results showed that the mean values of first-order uptake rate coefficients for in main channel and transient storage zone were 3.88×10-6s-1and 8.81×10-4s-1, respectively, and 7.80×10-6s-1and 7.98×10-8s-1for SRP, respectively. The average values of total uptake rate k-NH4 and k-SRP were 1.64×10-4s-1and 7.80×10-6s-1, respectively. The uptake lengths of Sw-NH4 and Sw-SRP were getting pretty big and approach 1632.88m and 25471.32m, respectively, suggesting a low probability to remove the nutrients by physical or biological processes. Relative to mountain headwater streams with low nutrient concentration, the studied reach had lower values of Vf-NH4and Vf-SRP, but higher U-NH4and U-SRP. Estimates of mass loss indicated that 93.82% of the uptake occurred in the transient storage zone, whereas 99.70% of the SRP uptake occurred in the main channel.