Identification and Scaling Behavior Assessment of the Dominant Hydrological Factors of Nitrate Concentrations in Streamflow

Nitrate-nitrogen (nitrate) pollution remains one of the most common causes of surface water quality degradation. Previous studies explored the fractal scaling behavior of controlling factors, but few studies investigated the change of scaling characteristics with time and the influence of a combination of factors on streamflow nitrate concentration (SFC). This study showed that a suite of hydrological factors impacting the SFC variations at multiple temporal scales can be determined using wavelet coherence analysis. The scaling behavior for controlling factors was evaluated using multifractal detrended fluctuation analysis. Results showed that streamflow and base flow exhibited persistent behavior, whereas the precipitation exhibited variable scaling behaviors that contributed to significant SFC fluctuations at multiple scales. Streamflow had substantial control on the SFC fluctuations when the time scale was shorter than 90 days. The combination of precipitation and streamflow formed the dominant processes impacting SFC at larger temporal scales (>90 days). These results provide an effective way to identify the factors influencing SFC variations across scales and predict the temporal evolution of SFC.