Abstract: This paper reports on the major cations (Ca, Mg, Na and K) and
arsenic (As) compositions of surface waters collected from major creeks, rivers
and lakes in Central Victoria (Australia). The surface waters were found to be
neutral to alkaline (pH 6.7–9.4), oxidised (average redox potential (Eh)
about 130 mV) and showed variable concentrations of dissolved ions (EC, about
51–4386μS/cm). The concen- trations of dissolved major cations in
surface waters were found to be in the order of Na>>Mg>Ca>K and in
soils the contents of metals followed an order of abundance as:
Ca>Mg>>K>Na. While Na was the least abundant in soils, it
registered the highest dissolved cation in surface waters. Of the four major
cations, the average concentration ofNa (98.7 mg/L) was attributed to the
weathering of feldspars and atmospheric input. Relatively highly dissolved
concentrations of Na and Mg compared with the world average values of rivers
reflected the weathering of rock and soil minerals within the catchments. The As soil level is naturally high(linked to lithology) as
reflected by high background soil values and mining operations are also
considered to be a contributory factor. Under relatively alkaline-oxidative
conditions low mobility of dissolved As (average about 7.9μg/L) was observed
in most of the surface waters with a few higher values (>15 μg/L) around
a sewage disposal site and mine tailings. Arsenic in soils is slowly released
into water under alkaline and/or lower Eh conditions. The efficient sink of Fe,
Al and Mn oxides acts as a barrier against the As release under near
neutral-oxidising conditions. High As content (average about 28.3 mg/kg) in
soils was found to be associated with Fe-hydroxides as revealed by XRD and SEM
analysis. The dissolved As concentration was found to be below the recommended
maximum levels for recreational water in all surface waters (lakes and rivers)
in the study area. Catchment lithology exerted the fundamental control on
surface water chemistry. Sites impacted by mining waste dumps showed a decline
in water quality.
Keywords: surface water, major cations, arsenic, soil, Australia
