A three-component hydrograph separation based on geochemical tracers in a tropical mountainous headwater catchment in northern Thailand

Abstract

Abstract. Land-use change in the mountainous parts of northern Thailand is reflected by an increased application of agrochemicals, which may be lost to surface and groundwater. The close relation between flow paths and contaminant transport within hydrological systems requires recognizing and understanding the dominant hydrological processes. To date, the vast majority of studies on runoff generation have been conducted in temperate regions. Tropical regions suffer from a general lack of data, and little is known about runoff generation processes. To fill this knowledge gap, a three-component hydrograph separation based on geochemical tracers was carried out in a steep, remote and monsoondominated study site (7 km 2 ) in northern Thailand. Silica and electrical conductivity (EC) were identified as useful tracers and were applied to calculate the fractions of groundwater (similar to pre-event water), shallow subsurface flow and surface runoff on stormflow. K + was a useful indicator for surface runoff dynamics, and Ca 2+ provided insights into groundwater behaviour. Nevertheless, neither measure was applicable for the quantification of runoff components. Cl − and further parameters (e.g. Na + , K + , and Mg 2+ ) were also not helpful for flow path identification, nor were their concentrations distinguishable among the components.Groundwater contributed the largest fractions to stormflow (62-80 %) throughout all events, followed by shallow subsurface flow (17-36 %) and surface runoff (2-13 %). Our results provide important insights into the dynamics of the runoff processes in the study area and may be used to assess the transport pattern of contaminants (i.e. agrochemicals) here.

Quantification of runoff generation from a combined glacier and <i>páramo</i> catchment within an Ecological Reserve in the Ecuadorian highlands

“…In all cases, the spring water displayed higher values with large variations; this suggests that some runoff could originate from deeper sources, from fissures and fractures in the rock, where longer residence and contact times have 10 increased the ion concentrations. Similar evidence was observed in other headwater catchments (Hugenschmidt et al, 2014;Scanlon et al, 2001). However, attention should be paid to the outliers, which provide clear evidence of meltwater resurgence from the glacier.…”

Isotopic Characterization of River Waters and Water Source Identification in an Inland River, Central Asia

“…In the arid and semi-arid areas, a combination of hydrology and environmental isotope technology ( 18 O, D) has been demonstrated to be a meritorious tool for investigating the process of water circulation [7,8]. Isotopes of particular interest for hydrological studies include the stable isotopes of water ( 18 O, D), which are incorporated within the water molecule (H 2 18 O, HD 16 O) [7], and because of isotope fractionation, they show regular spatial and temporal variations with the water cycle phase changes and diffusion [9][10][11].…”

“…It is reasonable to use isotopic techniques to study the water sources and supply mechanism of surface water and groundwater [6,[12][13][14][15], the evaporation of water bodies, and the mixing processes among various headwaters [16][17][18]. Isotope hydrograph separation (IHS) could provide a quantitative method to differentiate the replenishment of rivers for water resource management, especially in ungauged basins.…”

“…Surface water lines of the four headstreams were fitted. According to the spatial distribution of δ 18 O and δD from river water, most of the river water sample points were located above the GMWL and LMWL (δD = 8δ 18 O + 10 and δD = 7.1δ 18 O + 0.6), although some of them more closely approached the two meteoric water lines. An interesting feature of water isotopes in the Kaidu River is that several surface water sample measurements lie far above the LMWL (Figure 4), which indicates some of the Kaidu River water samples are significantly different from other streams with respect to their water isotope values.…”

“…Along with the mainstream flow direction, the evaporation effect has a considerable influence on the surface water. Deuterium excess (d-excess) is defined as d-excess = δD − 8δ 18 O by Dansgaard [22]. On the global scale, the d-excess values are about 10 for meteoric water [27].…”