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摘要
We investigated the distinctive shallow sub-surface hydrology of the southwest Western Australia (SWWA) dune calcarenite using observed rainfall and rainfall delta O-18; soil moisture, cave drip rate and dripwater delta O-18 over a six-year period: August 2005 March 2012. A lumped parameter hydrological model is developed to describe water fluxes and drip delta O-18. Comparison of observed data and model output allow us to assess the critical non-climatic karst hydrological processes that modify the precipitation delta O-18 signal and discuss the implications for speleothem paleoclimate records from this cave and those with a similar karst setting. Our findings include evidence of multiple reservoirs, characterised by distinct delta O-18 values and recharge responses (%26apos;low%26apos; and %26apos;high%26apos; flow sites). Dripwaters exhibit delta O-18 variations in wet versus dry years at low-flow sites receiving diffuse seepage from the epikarst with an attenuated isotopic composition that approximates mean rainfall. Recharge from high-magnitude rain events is stored in a secondary reservoir which is associated with high-flow dripwater that is 1 parts per thousand lower than our monitored low-flow sites (delta O-18). One drip site is characterised by mixed-flow behaviour and exhibits a non-linear threshold response after the cessation of drainage from a secondary reservoir following a record dry year (2006). Additionally, our results yield a better understanding of the vadose zone hydrology and dripwater characteristics in Quaternary age dune limestones. We show that flow to our monitored sites is dominated by diffuse flow with inferred transit times of less than one year. Diffuse flow appears to follow vertical preferential paths through the limestone reflecting differences in permeability and deep recharge into the host rock.
- 出版日期2013-3-15
