Abstract
Reforestation of degraded grasslands can increase the soil hydraulic conductivity and number of preferential flow pathways. However, it is not clear to what extent these changes affect streamflow responses and whether this depends on the event size. We, therefore, studied the hydrological response of two small catchments near Tacloban, Leyte (the Philippines): a degraded Imperata grassland catchment and a catchment that was reforested 23 years prior to our study. Precipitation, stream stage, and electrical conductivity were measured continuously from June to November 2013. Samples were taken from streamflow, precipitation, groundwater, and soil water for geochemical and stable isotope analyses. Streamflow and electrical conductivity changed rapidly during almost every event in the grassland catchment, but in the reforested catchment, these responses were much smaller and only occurred during large events. Streamflow was a mixture of groundwater and precipitation for both catchments, but the maximum event water contributions to streamflow were much larger for the degraded grassland than for the reforested catchment. The differences in the event water contributions and timing of the streamflow responses were observed across all event sizes, including a large tropical storm. Together with the low saturated hydraulic conductivity in the degraded catchment, these results suggest that overland flow occurred more frequently and was much more widespread in the degraded grassland than in the reforested catchment. We, therefore, conclude that reforestation of a degraded grassland can change the dominant flow pathways and restore the hydrological functioning if the forest soil is allowed to develop over a sufficiently long period.
| Original language | English |
|---|---|
| Pages (from-to) | 4128-4148 |
| Number of pages | 21 |
| Journal | Water Resources Research |
| Volume | 55 |
| Issue number | 5 |
| DOIs | |
| Publication status | Published - 1 May 2019 |
Funding
We thank Divina and Uldarico Padecio, leaders of the Manobo tribe, for permission to do research on their land. R. Arandela Magallanes and R. Dwight are thanked for help with the measurements at Manobo and Jos? June Bagay for help with the measurements at Basper. Many thanks also to Professor John Herbohn and Dr. Jack Baynes (University of the Sunshine Coast) and to Professors Victor Asio and Arturo Pasa and Dr. Nestor Gregorio (Visayas State University) for logistical support and fruitful discussions, to Ms. Ofelia Maranguit and Ms. Jertz Escala for help with the laboratory analyses under the supervision of Professor A. Ferraren (VSU), and to Dr. M. Waterloo (Acacia Water) for constructive feedback and suggestions. Special thanks are due to Kim Janzen and Professor Jeffrey McDonnell (University of Saskatchewan) for analysis of the isotope samples and to John Visser (formerly VU University Amsterdam) for the hydrochemical analyses. We thank David Chandler and two anonymous reviewers for their useful comments on this manuscript. This work was funded by ACIAR grant ASEM/2010/050 to J. Herbohn and a China Scholarship Council to J. Zhang.The precipitation, streamflow and EC data, and the isotope and stream chemistry data can be found in Table?S1 in the supporting information.
| Funders | Funder number |
|---|---|
| David Chandler | |
| EC data | |
| Visayas State University | |
| University of Saskatchewan | |
| Australian Centre for International Agricultural Research | ASEM/2010/050 |
| China Scholarship Council |
Keywords
- electrical conductivity
- hydrograph separation
- runoff generation mechanisms
- space-for-time substitution
- stable isotopes
- tropical reforestation
