Department of Forest Resources and Environmental Conservation

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Browsing Department of Forest Resources and Environmental Conservation by Subject "1402 Applied Economics"

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    Stream Runoff and Nitrate Recovery Times After Forest Disturbance in the USA and Japan
    Oda, Tomoki; Green, Mark B.; Urakawa, Rieko; Scanlon, Todd M.; Sebestyen, Stephen D.; McGuire, Kevin J.; Katsuyama, Masanori; Fukuzawa, Karibu; Adams, Mary Beth; Ohte, Nobuhito (American Geophysical Union, 2018-09-01)
    To understand mechanisms of long-term hydrological and biogeochemical recovery after forest disturbance, it is important to evaluate recovery times (i.e., time scales associated with the return to baseline or predisturbance 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, controlling factors have not yet been elucidated. Knowing these relationships will advance our understanding of each recovery process. The objectives of this study were to explore the relationship between runoff and nitrate recovery times and identify potential factors controlling each. We acquired long-term runoff and stream water nitrate concentration data from 20 sites in the USA and Japan. We then examined the relationship between runoff and nitrate recovery times at these multiple sites and use these relationships to discuss the ecosystem dynamics following forest disturbance. 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 catchments, 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 nitrogen was less available or less mobile in these catchments than water.
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    Time-Varying Storage-Water Age Relationships in a Catchment With a Mediterranean Climate
    Rodriguez, Nicolas B.; McGuire, Kevin J.; Klaus, Julian (American Geophysical Union, 2018-06-01)
    Recent studies on the relationships between catchment storage and water ages using Travel Time Distributions (TTDs), Residence Time Distributions (RTDs), and StorAge Selection (SAS) functions have led to the hypothesis that streamflow preferentially mobilizes younger water when catchment storage is high. This so-called “Inverse Storage Effect” (ISE) needs further evaluation in more catchments with diverse climates and physiographical features. In this work, we assessed the validity of the ISE in WS10 (H. J. Andrews forest, Oregon, USA), a forested headwater catchment in a Mediterranean climate. A conceptual model of the catchment, developed based on experimental observations of water flow paths in WS10, was calibrated to streamflow and δ18O in streamflow. Based on the calibrated model results, we determined RTDs, and streamflow TTDs and SAS functions by assuming that the soil reservoir and the groundwater reservoir act as well-mixed systems. The streamflow SAS functions and travel time dynamics showed that the ISE generally applies in WS10. Yet, during transitions from dry summer periods to wet winter periods and vice versa, the marked seasonal climate caused rapid and strong storage variations in the catchment, which led to deviations from the ISE. The seasonality of streamflow travel times in WS10 is the result of the seasonal contributions of younger water from the hillslopes added to the rather constant groundwater contributions of older water. The streamflow SAS functions were able to capture the relative importance of contrasting flow paths in the soils and in the bedrock highlighted by previous studies in WS10.