Temporal dynamics and projected future changes in nitrate leaching in a small river catchment dominated by under-drained clay soil grasslands: analysis of high-frequency monitoring data

Abstract

Water pollution has long been an issue due to its adverse effect on human health and the environment. This research has concentrated on a small river catchment dominated by grassland underlain by drained clay soil. It analysed temporal dynamics and projected future changes in nitrate leaching from the catchment. The types of nitrate response were classified according to the type of hysteresis loop obtained when concentration was plotted against discharge for each storm event. To narrow down the variable list and focus on the most relevant variables, stepwise multiple regression analysis was used. This work informed the understanding of how nitrate leaching patterns depend on source and transport, and the effect of antecedent conditions on hydrology and leaching patterns. The Newby Beck catchment is dominated by clockwise hysteresis events. Clockwise hysteresis storm events are source (or supply) limited. Nitrate concentrations within the catchment are governed by preparatory processes of nitrate production at source in the soil. Projected climate change may act to alter these preparatory processes through increasing temperatures and more severe droughts in summer, which would result in even more extreme nitrate leaching events. The transport from the catchment is driven by shallow subsurface flow through the drained clay soil and increasing precipitation with future climate change in winter will act to further facilitate the rapid transportation of nitrate to stream water. It was estimated that there is a 71% probability of future nitrate flux increasing by the 2050s and an 82% probability of future nitrate flux increasing by the 2080s. Mitigation measures that intercept water that is transporting this nitrate, combined with reduction of nitrate supplied by anthropogenic activities, will be the best choices.