Links between runoff generation, climate and nitrate-N leaching from forested catchments

摘要

To assess links between hydroclimatological factors and NO3--N concentrations in streamflow from boreal forests with shallow soils, data from two catchments were analyzed. TOPMODEL was used to calculate the surface runoff fraction, daily dynamics of soil moisture, groundwater levels, and extensions of saturated areas. The stable isotope O-18 was used for isotopic hydrograph separation (IHS) during one snowmelt season. Air-temperature and flow increase were the dominating factors explaining annual NO3--N dynamics. Correlation also was found between NO3--N concentrations and the surface runoff fraction. Increased concentrations during times of shallow groundwater were found both during cold and warm periods in one catchment. In the other, shallow groundwater was correlated to decreasing concentrations during cold periods, and increasing concentrations during warm periods. A two component model of event and pre-event water fractions and corresponding NO3--N concentrations was set up for the snowmelt season. Model predictions mirrored NO3--N concentration s during the first five days of the snowmelt. After that, the model overestimated NO3--N concentrations, which indicates retention of NO3--N in the event water fraction, originating from the snowmelt. The highest concentrations occurred during the initiations of flow increase, which indicates flushing of surficial NO3--N. References: 20