Al. Herczeg et al., CHEMICAL AND ISOTOPIC INDICATORS OF POINT-SOURCE RECHARGE TO A KARST AQUIFER, SOUTH AUSTRALIA, Journal of hydrology, 192(1-4), 1997, pp. 271-299
Several hundred sinkholes, swamps and open drainage boreholes througho
ut the semi-arid to sub-humid areas of the southeast of South Australi
a are potential recharge sites to the upper part of the Gambler Limest
one aquifer. This paper presents the results from a hydrochemical (Cl-
and carbonate chemistry) and isotopic (delta(2)H, delta(18)O and Cl-3
6) study used to estimate the importance of localised recharge from th
ese point-source features to the karstic groundwater system. Results s
how that water recharging the groundwater via point-source features is
detectable only on a local scale. Chemical and isotopic compositions
of groundwaters more than 150 m from the larger of the point-source fe
atures are indistinguishable from regional groundwater compositions. C
hloride concentrations, carbonate chemistry, and isotope data show tha
t annual input of water via point sources contributes less than 10% of
total recharge, with diffuse recharge providing the remainder to the
study area as a whole. Point-source recharge is generally intermittent
, and was observed to occur only for a few days at a time and only aft
er a threshold of sustained rainfall had been exceeded (i.e. greater t
han 2.5 mm day(-1) for more than 3 days). The stable isotopic composit
ion of waters recharging via sinkholes tends to be enriched in H-2 and
O-18 relative to regional groundwater and local precipitation. This i
s probably caused by a small degree of evaporation (less than 5% of wa
ter falling within the catchment) occurring during winter at high rela
tive humidity (greater than 95%) before recharge, Cl-36 from weapons t
esting is detectable in groundwaters near sinkholes and indicates sign
ificant retardation of Cl- within soils of the respective sub-drainage
systems. Recharge has therefore occurred within the past 30 years, bu
t cannot be quantified with any reliable precision from the Cl-36 data
. (C) 1997 Elsevier Science B.V.