Contrasting transit times of water from peatlands and eucalypt forests in the Australian Alps determined by tritium: implications for vulnerability and the source of water in upland catchments

Abstract

Peatlands are a distinctive and important component of many upland regions that commonly contain distinctive flora and fauna which are different from those of adjacent forests and grasslands. Peatlands also represent a significant long-term store of organic carbon. While their environmental importance has long since been recognised, water transit times within peatlands are not well understood. This study uses tritium ( 3 H) to estimate the mean transit times of water from peatlands and from adjacent gullies that contain eucalypt forests in the Victorian Alps (Australia). The 3 H activities of the peatland water range from 2.7 to 3.3 tritium units (TUs), which overlap the measured (2.9 to 3.0 TU) and expected (2.8 to 3.2 TU) average 3 H activities of rainfall in this region. Even accounting for seasonal recharge by rainfall with higher 3 H activities, the mean transit times of the peatland waters are < 6.5 years and may be less than 2 years. Water from adjacent eucalypt forest streams has 3 H activities of 1.6 to 2.1 TU, implying much longer mean transit times of 5 to 29 years. Cation / Cl and Si / Cl ratios are higher in the eucalypt forest streams than the peatland waters and both of these water stores have higher cation / Cl and Si / Cl ratios than rainfall. The major ion geochemistry reflects the degree of silicate weathering in these catchments that is controlled by both transit times and aquifer lithology. The short transit times imply that, unlike the eucalypt forests, the peatlands do not represent a long-lived store of water for the local river systems. Additionally, the peatlands are susceptible to drying out during drought, which renders them vulnerable to damage by the periodic bushfires that occur in this region.

Origin and formation mechanism of salty water in Zuli River catchment of the Yellow River

“…Groundwater age is an extremely important indicator of the groundwater replenishment (Bethke & Johnson, ; Cresswell et al., ; Jasechko, ). Tritium ( 3 H), a radioactive isotope of hydrogen with a concentration that spiked in precipitation approximately 50 years ago as a result of aboveground thermonuclear testing, is commonly applied in hydrologic cycle research to determine whether modern water supplies exist (Cartwright & Morgenstern, ; Egboka et al., ; Morgenstern et al., ; Robertson & Cherry, ; Solomon et al., ; Young et al., ). Many studies have shown that water with 3 H contents of <1 TU is regarded as having a pre‐1952 age (Farid et al., ).…”

“…In addition, quantifying groundwater age by radioisotopes to trace groundwater migration pathways is also effective for identifying regional water cycles through isotopic methods (Bethke & Johnson, ; Cartwright, Cendon, Currell, & Meredith, ; Clark & Fritz, ; Cresswell, Jacobson, Wischusen, & Fifield, ; Hagedorn, ; Kalin, ). For example, tritium ( 3 H), a radioactive isotope of hydrogen with a concentration that spiked in precipitation approximately 50 years ago as a result of aboveground thermonuclear testing, is commonly applied in hydrologic cycle research to determine whether modern water supplies exist (Cartwright & Morgenstern, ; Egboka, Cherry, Farvolden, & Frind, ; Morgenstern, Stewart, & Stenger, ; Robertson & Cherry, ; Solomon, Poreda, Cook, & Hunt, ; Young, Broughton, Bradd, & Holland, ).…”

The impact of well drawdowns on the mixing process of river water and groundwater and water quality in a riverside well field, Northeast China

“…It can therefore be concluded that EC was the only environmental tracer that provided results consistent with those of the pumping well dynamics method for the three different drawdowns. However, results calculated by using TDS and temperature as tracers were not as consistent with the pumping well dynamics method as EC due to the applicability of different parameters and the impact of the uncertainty (Cartwright & Morgenstern, ). Therefore, in the study area, EC can be effectively used as environmental tracers to ascertain the mixing ratio between the river water and the groundwater.…”

Identification of groundwater mean transit times of precipitation and riverbank infiltration by two‐component lumped parameter models

“…We tested six TTDs commonly applied in hydrologic systems: the exponential, linear, exponential‐piston flow (EPF), linear‐piston flow (LPF), advection–dispersion (AD, Maloszewski & Zuber, ; Cook & Böhlke, ), and the gamma model (Kirchner, Feng, & Neal, ). Although the EPF and AD models have been used in riverbank infiltration studies (e.g., Kármán, Maloszewski, Deák, Fórizs, & Szabó, ; Maloszewski, Rauert, Trimborn, Herrmann, & Rau, ; Stichler et al, ; Stichler et al, ) and in groundwater studies (e.g., Cartwright & Morgenstern, ; M. K. Stewart, Morgenstern, Gusyev, & Małoszewski, ), the exponential and gamma models have been widely applied for catchment mTT modelling (cf. K. J. McGuire & McDonnell, ; Hrachowitz et al, ).…”

“…To improve the convergence of Monte Carlo simulations, we limited P D to 1 (cf. Cartwright & Morgenstern, ), which is appropriate for kilometre‐scale flow systems (Mook & Rozanski, ). The range of the shape parameter ( α ) in the gamma model was limited to 10, following Timbe et al () and M. K. Stewart et al ().…”