Long-term changes of water and chemical budgets after clear-cutting of a small headwater catchment in Japan

To understand the mechanisms of hydrological and biogeochemical processes of forest ecosystems, long term monitoring of changes in water and chemical budgets after forest disturbance is important. Previous studies have generally focused on changes in stream runoff and water chemistry. However, the long term changes in forest-canopy ecosystems such as rainfall partitioning and the chemical budget of the canopy have not been sufficiently considered. Therefore, the objectives of this study were to evaluate the long-term changes of input and output budgets of water and chemistry after clear-cutting of forest catchment. The study was conducted in a pair of small headwater catchments, one of which was clear-cut in 1999 and then planted with the same species in 2000; the other served as a control. After forest cutting, annual runoff increased 200-300 mm/yr and the higher runoff still remained 14 years later. The interception ratio in the clear-cut catchment was less than 10% of precipitation, whereas that in the control catchment was 20-24% of precipitation. Interception rate was still lower in the young forest compared with the mature forest, despite similar transpiration rate. With regard to chemistry, Cl- and SO42- concentrations in stream water decreased after cutting and remained lower 14 years later. On the other hand, NO3- concentration increased and finally returned to its pre-cut level. The atmospheric deposition inputs, such as those of Cl-, Na+, and SO42-, remained lower in the clear-cut catchment than in the control. On the other hand, input of K+, Mg2+, and Ca2+ originating from canopy leaching became significantly higher in the clear-cut catchment compared with those in the control. These results suggest that not only the biological processes such as water and chemical uptake by plants, but also changes in canopy physical processes such as canopy interception and chemical scavenging, affected the long-term response of stream runoff and chemistry following the cutting.