生活污水为主要补给源的城郊排水沟渠氮磷滞留特征

为揭示生活污水补给影响下排水沟渠氮、磷滞留特征,以合肥市城郊结合部的关镇河支渠为对象,以NH₄Cl和KH₂PO₄为添加营养盐,以NaCl为保守型示踪剂,开展5次现场示踪试验. 在此基础上,利用OTIS(one-dimensional transport with inflow and storage)模型估算D(扩散系数)、A(渠道过水断面面积)、A_s(暂态存储区断面面积)、α(暂态存储交换系数)、λ(主流区溶质一阶吸收系数)和λ_s(暂态存储区吸收系数)；并利用营养螺旋原理,计算营养盐的S_w(吸收长度)、V_f(吸收速度)和U(吸收速率)等. 结果表明:①A_s/A具有随流量减小而增大的变化特征,平均值为0.35；5次试验得到的α均处在10-3数量级水平,平均值为2.49×10-3 s-1. ②S_w-NH₄和S_w-PO₄(分别表示NH₄-N和PO₄-P的S_w,下同)均较大,最大值分别达934 020、47 518 m,意味着关镇河支渠已基本不具备氮、磷滞留能力；而S_w-NH₄和S_w-PO₄均不同程度地出现负值,表明该支渠还具有“源”的作用. ③V_f-NH₄与河水平均深度、渠道流量均呈显著负相关,V_f-PO₄和U-PO₄与渠道水面宽度均呈显著正相关. ④NH₄-N和PO₄-P的营养螺旋指标与其相应质量浓度背景值无明显相关性. 

Nitrogen and Phosphate Retention in a Drainage Ditch Dominated by Domestic Sewage in a Suburban Area of Hefei City

Nitrogen and phosphorus retention for a typical drainage ditch in Guanzhenhe Branch, a first-order stream dominated by domestic sewage in the rural-urban continuum of Hefei, was characterized. Field tracer experiments were carried out for five replications by addition of a conservative tracer (NaCl) and nutrients (NH₄Cl and KH₂PO₄) along the study reach. Based on the experimental data, hydrological parameters (e.g., dispersion coefficient D, stream channel cross-sectional area A, storage zone cross-sectional area A_s, and stream storage zone exchange coefficient α) and the first-order nutrient decay coefficients (e.g., decay coefficient in main channel λ and decay coefficient in storage zone λ_s), were estimated with the transient storage OTIS (one-dimensional transport with inflow and storage) model. Nutrient spiraling metrics (i.e., uptake length S_w , mass transfer coefficient V_f, and nutrient uptake rate U) were subsequently calculated based on the nutrient spiraling theory. Regression and correlation analysis were further conducted with SPSS statistical software. The results showed that:1) The average value of As/A was 0.35, and was significantly negatively correlated with discharge (Q). 2) The order of magnitude of α was 10-3, while the mean value of α was 2.49×10-3 s-1. S_w -NH₄ and S_w -PO₄ (S_w of NH₄-N and PO₄-P) reached their maximum values of 934,0 and 47,8 m, respectively, indicating that Guanzhenhe Branch was not capable of retaining nutrients efficiently. Meanwhile, the negative values of S_w -NH₄ and S_w -PO₄ suggested that the study reach even acted as a nutrient source. 3) Correlation analysis results showed that V_f-NH₄ was negatively correlated with water depth and Q, respectively. In addition, both V_f-NH₄ and U_f-PO₄ increased with stream width. 4) Nutrient spiraling metrics were not statistically related to ambient concentrations of NH₄-N and PO₄-P in regression analysis. In general, high nutrient concentrations restricted the effect of nutrient retention in Guanzhenhe Branch. Excessive nutrient sources coming from domestic sewage should be reduced to improve the stream retention capacity.