Intra- and inter-storm oxygen-18 and deuterium variations of rain, throughfall, and stemflow, and two-component hydrograph separation in a small forested catchment in Japan

Abstract

Inter-and intra-storm oxygen-18 variations in rain, throughfall, and stemflow were measured to estimate accurate "new" water inputs to the watershed within a 0.84-ha watershed planted with 80-year-old Cryptomeria japonica and Chamaecyparis obutusa artificial forest at the Hitachi Ohta experimental watershed in Japan. In addition two-component hydrograph separation using oxygen-18 concentrations was conducted with four types of "new" water concentration: (1) incremental volume-weighted mean concentrations of rainfall; (2) constant concentrations of rainfall; (3) incremental volume-weighted mean concentrations of throughfall; and (4) constant concentrations of throughfall. Six storms from June to October 2000 were investigated. In the 26 July, 24 September, and 29 October storms, old-water percentages at the hydrograph peak were more than 56.4%, 66.6%, and 80.4%, respectively. In the 24 September and 29 October storms, the old-water contribution estimated by incremental volume-weighted mean concentrations of throughfall was the greatest. On the other hand, this was the smallest after the 26 July storm. Thus, by estimating the "new" water inputs more accurately, the "old" water contribution could be either large or small. In addition, there was a relative difference of about 5-10% between old water percentages calculated from the four types of "new" water. The uncertainty associated with the analysis of oxygen-18 concentrations was up to 4.8%. Thus the difference in estimates of "new" water affected the "old" water percentage more than the uncertainty of the two-component model itself.

Temporal variations of isotopic compositions in gross rainfall, throughfall, and stemflow under a Japanese cedar forest during a typhoon event

“…On the other hand, stemflow isotopic characteristics especially for oxygen and hydrogen isotopes are poorly understood. Kubota and Tsuboyama (2003) compared isotopic composition of throughfall and stemflow water collected by bulk sampling during a rainfall event and reported that the oxygen isotopic composition in stemflow is higher than that in throughfall, though no specific reasons were given for the isotopic differences.…”

Analyzing Effects of Shrub Canopy on Throughfall and Phreatic Water Using Water Isotopes, Western China

“…End-member mixing models can calculate contributions of different water sources when the isotope value of each water source can be determined [11,26]. During the sampling period, the rainfall event of August 15, 2003 (14.8 mm/day) was used to calculate its contribution in sequential 5 days (August [16][17][18][19][20] since there had few rainfalls from August 14 to 20 except for August 15. Two-source mixing model with single isotope is used to calculate the contributions of two sources, as follows: …”

“…The water stable isotope ratios can benefit for analyzing water flux variations through the ecosystem or plant individual [9][10][11][12], such as plant water use [13][14][15][16], stemflow, throughfall, and evaporation rate [17,18]. At a large scale, the rain forest plays an important role in the regional hydrological cycle by stable isotope analysis [19].…”

“…Variations in the stable isotope composition of meteoric waters are used to identify different plant water sources [3,20,21], and plant water is mainly from the top 50 cm of the soil [13]. Moreover, Kubota and Tsuboyama studied how new water inputs (rainfall, throughfall and stemflow) affected the old water percentage within soil-root-plant system by using stable isotope method [17].…”

Effect of Hydrograph Separation on Suspended Sediment Concentration Predictions in a Forested Headwater with Thick Soil and Weathered Gneiss Layers

“…For example, by measuring the stable isotope ratio, runoff water and event rainwater can be separated into two components: pre-event water and event water [17][18][19]. Many reports describe the simultaneous observations of dissolved ion concentration and stable isotope ratio in runoff water [20,21]; however, only a few studies report simultaneous observations of SS concentration and stable isotope ratio in runoff water.…”