Stream runoff and nitrate recovery times after forest disturbance in US and Japan

To understand mechanisms of long-term hydrological and biogeochemical recovery processes after forest disturbance, it is important to evaluate recovery times (i.e. timescales associated with the return to baseline, or pre-disturbance, conditions) of stream runoff and nitrate concentration. Previous studies have focused on either the response of runoff or nitrate concentration, and some have specifically addressed recovery times following disturbance. However, few studies have focused on the both runoff and nitrate recovery times. The objectives of this study were to explore runoff and nitrate recovery times, and identify potential factors controlling each. We acquired data on long-term runoff and streamwater nitrate concentrations from 20 sites in the eastern USA and Japan that had at least 8 years (and up to 50 years) of post disturbance data. We then examined the relationship between runoff and nitrate recovery times at these multiple sites, and use these to discuss the ecosystem dynamics following forest disturbance. Hydrologic recovery times ranged from 0 to 20 years. Nitrate recovery times ranged from 2 to 17 years. Nitrate response was detected at all study sites, while runoff responses were detected at all sites with disturbance intensities greater than 75% of the catchment area. The runoff recovery time was significantly correlated with the nitrate recovery time for catchments that had a runoff response. For these events, hydrological recovery times were slower than nitrate recovery times. The relationship between these two recovery times suggests that forest regeneration was a common control on both recovery times. However, the faster recovery time for nitrate suggests that N was less available or less mobile in these catchments than water (energy limited evapotranspiration).