Effects of channel morphology on nitrate retention in a headwater agricultural stream in Lake Chaohu Basin, China

Five field tracer experiments and relevant detailed investigations of physical characterizations were conducted to investigate the effects of channel geomorphic settings on nitrate uptake efficiency on a 310-m long geomorphically distinct stream reach in a headwater agricultural stream in Hefei District, Lake Chaohu Basin. The model-fitted parameters from the one-dimensional transport with inflow and storage model were used to estimate the transient storage metric (Fmed200\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {F}_{\mathrm{med}}^{200} $$\end{document}) and determine the total nitrate uptake coefficient (k) for the study reach. And then, a nutrient spiraling approach was applied to reach-scale nitrate uptake estimates (Sw, Vf, and U). The results showed that the main channel was the major contributor to nitrate uptake retention, and the higher geomorphic complexity might result in better nitrate uptake efficiency. The partial least squares regression (PLSR) analysis showed strong correlations between the independent variables as geomorphic settings, Reynolds number and transient storage, and the dependent variables as nitrate uptake metrics, which further underscored the importance of stream physical characteristics on measurement of stream nitrate uptake.