源头溪流氮磷耦合吸收效应及动力学模拟

为揭示源头溪流氮磷耦合吸收作用机制，选择NaCl和NaBr为保守型示踪剂、KNO₃和KH₂PO₄为添加营养盐，于2017年10月~2018年3月在合肥城郊的2条源头溪流，开展5次由单、双营养盐添加构成的示踪试验，利用TASCC技术方法，分别以Michaelis-Menten（M-M）方程和双营养耦合吸收曲面模型拟合营养盐吸收动力学过程.结果表明，双添加试验的NO₃^-N、PO₄^-P吸收速率均明显高于单添加情形，意味着溪流中NO₃^-N与PO₄^-P吸收存在相互促进作用；双营养耦合吸收响应曲面直观展示了氮、磷营养盐不同浓度水平及浓度比情形下吸收速率的演化趋势，诠释了较低浓度水平下溪流NO₃^-N（或PO₄^-P）吸收速率随PO₄^-P（或NO₃^-N）可利用量增加而增大的作用机制；两种动力学模型在NO₃^-N、PO₄^-P最大吸收速率拟合结果上均存在不同程度的偏差，其中M-M方程低估了U_max-N和U_max-P，相应幅度分别达3.91%~16.11%、3.23%~23.63%.

Coupling uptake kinetics and mechanism of nitrogen and phosphorus in headwater streams

Five conservative tracer tests including single nutrient and dual-nutrient injection were conducted to reveal the coupling mechanism of nitrogen and phosphorus uptake in two headwater streams of Ershibu River in the suburb of Hefei, Chaohu Lake Basin, from October 2017 to March 2018. NaCl and NaBr were selected as the conservative tracers; the reactive nutrients were KNO₃ and KH₂PO₄. Based on the TASCC (Tracer Additions for Spiraling Curve Characterization) method, the Michaelis-Menten (M-M) model and the two-substrate M-M response surface model were applied to simulate the kinetics of nutrients uptake. The results showed that the uptake rates of NO₃^-N and PO₄^-P in the dual-nutrient injection test were significantly higher than those obtained in the single nutrient injection test, which implied that mutual promotion between NO₃^-N and PO₄^-P for nutrient uptake in the two headwater streams. The dual-nutrient uptake response surfaces presented the evolutionary trends of uptake rates at different concentrations and ratios of nitrogen and phosphorus. Additionally, it also explained the interaction mechanism of NO₃^-N (or PO₄^-P) uptake rate increasing with the increase of the available PO₄^-P (or NO₃^-N) at their low concentration. The fitting results of NO₃^-N and PO₄^-P maximum uptake rates (U_max-N and U_max-P) obtained by the two kinetic models presented deviations in a certain degree. The parameters of U_max-N and U_max-P were underestimated by the M-M model ranging from 3.91%~16.11% and 3.23%~23.63%, respectively.