Dynamics of Stream Water Quality during Snowmelt and Rainfall - Runoff Events in a Small Agricultural Catchment

摘要

Surface water quality can vary a lot with fluctuating discharge during a Rainfall - runoff event. This paper uses a set of hydrologieal and hydrochemical variables to explain concentration-discharge loops and hysteresis of NO_3~-, NH_4~+ and total suspended solids in a brook dewatering a small upland agricultural catchment in the Czech Republic. Our study is based on data collected by a continuous monitoring approach provided by an automatic ISCO sampler both from snow thawing and rainfall - runoff events. Methods of correlation, regression and principal component analysis (PCA) were employed to reveal possible relationships among the variables. For NO_3~- and NH_4~+, we found several types of concentration-discharge loops due to the loop rotation direction and also the loop curvature shape, in mutual combinations, no matter which type of a hydrologieal event it was related to. PCA indicated that NO_3~- loops correlated mostly with the length of a rising hydrograph limb and with the slope of the initial phase of a falling hydrograph limb, 5-day amount of precipitation and runoff coefficient. In case of NH_4~+, the concentrations usually increased with elevated discharge, whereas PCA did not detect any closer linkages. For suspended solids, an unambiguous positive monotonic relationship was discovered. Although no definite pattern was found, this study showed the necessity of a continuous water quality monitoring system as an approach for capturing and understanding relationships between solute concentrations and runoff formation for tracing and modelling catchment pollution sources and describing transport processes.