[AHW34-07] Stable isotope-based approach to validate effects of canopy openness and under story on soil water in a Japanese forest plantation
Keywords:Preferential flow, Zero tension lysimeter
Japan has the forests that cover more than 66 % of total land area, are distributed in hilly and complex topography areas. The 41 % of those forests are plantations. Recent climate change occur the increasing risks of drought and torrential rain increases the importance of water recharge function which planted forest currented most of Japanese forest has.
Many researchers have studied the effects of plantation thinning on forest environments, including plantation thinning-induced changes in soil water, which recharges ground water. However, most of these studies have sampled only either preferential flow or matrix flow. To properly understand soil water movement, soil water must be classified into matrix flow and preferential flow, and we must sample and analyze them separately. Therefore, our purpose is to reveal the differences in the water stable isotope rates in soil water on different vegetation distributions to consider the change of soil water.
We used suction lysimeters adding 60 kPa and zero-tension lysimeters to collect two types soil water separately. We used modular zero-tension plate lysimeters which improve the problems in conventional zero-tension plate lysimeter of both low water collection efficiency by unsaturated soil on the plate and soil disturbance by inserting the plate. In addition, we collected throughfall and open rainfall, and measured soil moisture, soil water potential, floor evaporation and radiation. We used soil moisture sensor (EC-5, ECHO and ODYSSEY) for soil moisture, tensiometer for soil water potential, value got from weighing lysimeter for floor evaporation and PAR sensor for radiation. We analyzed water stable isotope rate in the water collected in our study plots using Picarro L2120-i δD/δ18O Isotopic Water Analyzer. We considered about the change of soil water by different vegetation distributions using the difference of stable isotope rate in the water.
Matrix flow tended to be isotopically heavier under open canopy than under closed canopy, and isotopically heavier in areas with no understory vegetation than in areas with understory vegetation. Therefor, the time series change in water stable isotope rate in Matrix water became smaller as it gets deeper. Preferential flow tended to be almost the same water stable isotope rate as throughfall. But, that stable isotope rate is heavier under open canopy than under closed canopy. We could see the former tendency regarding preferential flow better in heavy rain events than in light rain events, and the trend suggests mixing with matrix flow in the light rain. There was little difference between water stable isotope rates of throughfall in different vegetation distributions.
The implications of these results suggest that soil water which recharges ground water is isotopically heavy in a degraded plantation, and becomes isotopically heavier with the increase in forest floor evaporation after plantation thinning, but becomes isotopically lighter as understory vegetation grows.
Many researchers have studied the effects of plantation thinning on forest environments, including plantation thinning-induced changes in soil water, which recharges ground water. However, most of these studies have sampled only either preferential flow or matrix flow. To properly understand soil water movement, soil water must be classified into matrix flow and preferential flow, and we must sample and analyze them separately. Therefore, our purpose is to reveal the differences in the water stable isotope rates in soil water on different vegetation distributions to consider the change of soil water.
We used suction lysimeters adding 60 kPa and zero-tension lysimeters to collect two types soil water separately. We used modular zero-tension plate lysimeters which improve the problems in conventional zero-tension plate lysimeter of both low water collection efficiency by unsaturated soil on the plate and soil disturbance by inserting the plate. In addition, we collected throughfall and open rainfall, and measured soil moisture, soil water potential, floor evaporation and radiation. We used soil moisture sensor (EC-5, ECHO and ODYSSEY) for soil moisture, tensiometer for soil water potential, value got from weighing lysimeter for floor evaporation and PAR sensor for radiation. We analyzed water stable isotope rate in the water collected in our study plots using Picarro L2120-i δD/δ18O Isotopic Water Analyzer. We considered about the change of soil water by different vegetation distributions using the difference of stable isotope rate in the water.
Matrix flow tended to be isotopically heavier under open canopy than under closed canopy, and isotopically heavier in areas with no understory vegetation than in areas with understory vegetation. Therefor, the time series change in water stable isotope rate in Matrix water became smaller as it gets deeper. Preferential flow tended to be almost the same water stable isotope rate as throughfall. But, that stable isotope rate is heavier under open canopy than under closed canopy. We could see the former tendency regarding preferential flow better in heavy rain events than in light rain events, and the trend suggests mixing with matrix flow in the light rain. There was little difference between water stable isotope rates of throughfall in different vegetation distributions.
The implications of these results suggest that soil water which recharges ground water is isotopically heavy in a degraded plantation, and becomes isotopically heavier with the increase in forest floor evaporation after plantation thinning, but becomes isotopically lighter as understory vegetation grows.