Methods were developed for the determination of methylmercury in natural waters and
sediments based on steam distillation and aqueous phase ethylation followed by gas chromatography-atomic fluorescence spectrometry. The methods were shown to be free
from measurable artefactual methylation of inorganic mercury and offered improved
sample throughput over existing methods. Improvements were made to existing
methods for the determination of total mercury in biota, sediments and natural waters
and dissolved mercury species in natural waters. These methods were applied to the
study of mercury cycling in two remote field sites.
The cycling of mercury species was studied in Lake Murray in Western Province,
Papua New Guinea, which has been historically noted as a region of high mercury
concentrations in fish. Concentrations of methylmercury and total mercury in the water
column were found to be variable and consistent with non-contaminated lake systems.
Concentrations of methylmercury and total mercury in the sediments were also found to
be low, except for in the south of the lake, which was influenced by an intermittent
supply of water and sediments with elevated mercury concentrations from the
Strickland River. Methylmercury concentrations in the sediments were generally higher
in the backwater areas due to littoral processes. The low concentrations of
methylmercury in the sediments and waters were inconsistent with other systems
previously studied in the northern hemisphere, showing a link between high mercury
concentrations in fish and high concentrations of methylmercury in waters or sediments.
Therefore, the biota of Lake Murray were studied in order to account for the differences
between this and other systems.
A study was conducted of the stable isotope ratios of carbon and nitrogen in biota from
Lake Murray to elucidate key food-web interactions. This study revealed that the
dominant carbon source for fish in the lake is plankton, although algae and macrophytes
may also be involved in the food-web. The methylmercury bioaccumulation factors
between trophic levels were similar to those measured in temperate systems of the
northern hemisphere. The high concentrations of methylmercury, observed in
piscivorous fish, were shown to be a consequence of the complex food-web and the
number of trophic levels in the food-chains.
The cycling of mercury species was studied in Lake Gordon and Lake Pedder in
southwest Tasmania, which has recently been identified as being in a region of high
mercury concentrations in trout and eels. The concentrations of total mercury were
found to be reasonably uniform in the waters of both lakes, spatially and temporally.
The concentrations of methylmercury in the waters were seasonally variable, and were
consistently lower in Lake Pedder than in Lake Gordon. Dilution of methylmercury
concentrations by precipitation direct to the lake surface, probably accounts for the
most of the difference in methylmercury concentrations between the lakes. Owing to
the long residence time of water in Lake Gordon, this reservoir mixes inputs of water
with varying methylmercury concentrations. Concentrations of total mercury and
methylmercury in submerged soils were low and depth profiles of mercury species in
the water column did not show evidence of a gradient of mercury concentrations due to
releases from the sediments. The concentrations of methylmercury observed in the
water column are consistent with the concentrations observed in the fish.
A budget of the mercury inputs and outputs to Lake Gordon showed that in-lake
processes and sources in the catchment areas both contributed significantly to the
concentrations of methylmercury in the lake. The methylation of mercury in Lake
Gordon appeared to mainly occur in the surface waters (< 10 m) and was not consistent
with processes leading to the methylation of mercury at the oxic/anoxic boundary
observed in seepage lakes in Wisconsin. The concentrations of total mercury and
methylmercury in bogs in the catchment areas of Lakes Gordon and Pedder, were high
and governed by the concentration of organic matter in the sediments. The processes
involved in the supply of mercury species from the Lake Gordon and Lake Pedder
catchments appear to be similar to those in drainage lakes in the temperate and boreal
regions of the northern hemisphere. The formation of the Lake Gordon and Lake
Pedder reservoirs appears to have had little impact on the mean annual concentrations
of methylmercury released to the downstream environment.
| Identifer | oai:union.ndltd.org:ADTP/218762 |
| Date | January 1998 |
| Creators | Bowles, Karl C., n/a |
| Publisher | University of Canberra. School of Resource, Environmental & Heritage Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Karl C. Bowles |
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