For various reasons, existing methods for the assessment of aquatic pollution do not always
adequately address the way in which contaminants affect receiving environments and their
component ecosystems. The main advantage of biological assessment over the measurements
of physical and chemical aspects of water quality is that biota provide an integrated response
to all prevailing influences in their environment. Biological assessment protocols have been
developed for a range of test organisms, from bacteria to mammals using measurement from
molecular biomarkers to indicators at the population or community level of organisation.
Macroinvertebrates in particular have been popular for ecological assessment of habitat and
water quality because they are small and straight forward to sample and identify using
relatively simple and inexpensive equipment and readily available taxonomic keys.
However, various biological assessment techniques also have their limitations. Field-based
assessment of biological communities does not provide direct evidence to determine
underlying causal relationships, while laboratory or mesocosm toxicity tests are criticised for
their limited ability to extrapolate to natural field conditions. To help bridge the gap, this
thesis aims to investigate the efficacy of using caged macroinvertebrates in situ to assess the
ecological condition of aquatic environments, and whether a causal relationship can be
established when macroinvertebrates are deployed in situ at sites known to have impaired
water quality. Endpoints employed in this thesis include survival, measurements of
morphology (as a surrogate for growth) and condition and, for trials assessing sites that
receive mine drainage, the tissue concentration of certain trace metals.
Development of an in situ approach to water quality monitoring and assessment will
potentially provide methods for use by resource managers, community groups and aquatic
researchers that are less expensive and faster to run than existing methods and will
complement other approaches employed in the assessment of water quality.
In situ testing of water quality using macroinvertebrates requires the collection, handling,
caging, deployment and retrieval of test organisms at sites of suspected pollutant impact. As
such procedural factors may affect test organisms and potentially confound their responses, it
is important to consider and understand as many of these factors as possible. Aquatic
macroinvertebrates held in finer mesh cages had larger heads than in coarser mesh cages. This
was likely due to increased substrate available for growth of epilithon and periphyton on
which the caged organisms could graze. Caging density had no effect on amphipod mortality
over the trial period, however, individuals held at higher densities increased in size (as
indicated by longer dorsal lengths) more than those held at lower or intermediate densities.
Temporary storage of test organisms in laboratory aquaria may facilitate the collection of
abundances required for in situ trials, however, tanked individuals were smaller and had lower
biomasses than individuals collected and deployed immediately. While this is likely to result
from differences in feeding during the storage period, it is also possible that tank storage and
the ?double handling? deleteriously affected them, or reduced their tolerance.
The effects of transplanting macroinvertebrates between sites varied considerably depending
on the characteristics of "source" and "transplant" sites. Certain taxa suffered marked
mortality within 24 hours even at their source site, indicating an adverse effect of the caging
itself, or perhaps via the change in food, shelter or microclimate which could potentially
render them unsuitable as test organisms in caging studies. Other taxa did not differ in
survival or body size when relocated between sites, with some evidence of increased growth
at sites dissimilar from their source site. In general, organisms relocated to sites that are
"similar" to their source environment performed less well at the transplant site. However,
organisms transplanted to "dissimilar" sites were found to be bigger than those caged and
deployed back to the source site.
When employed to assess known pollution scenarios in and around Canberra,
macroinvertebrate responses were, in some instances, able to be linked to specific
environmental parameters or combinations thereof. In Case Study 1, findings varied in
relation to the response endpoint being examined, and between test species, although
concentrations of metals were significantly higher in tissue of macroinvertebrates deployed at
the impact site downstream of the abandoned Captains Flat mine and increased with time
exposed. In Case Study 2, freshwater shrimp suffered significant mortality within 24 hours of
deployment at the impact sites, with larger individuals more susceptible at sites receiving
urban stormwater runoff. While various biological effects were most closely correlated with
ammonia concentrations at the site, different body size endpoints were affected in opposite
ways. In Case Study 3, body size endpoints for one test organism varied consistently with
respect to site and time factors, but none of the changes could be linked to any of the
environmental data collected. Response variables for a different test species also indicated
significant effects arising from both deployment site and time, however, each endpoint
responded in a different way to the treatment factors, and aligned with different
combinations of environmental data.
In general, linking of macroinvertebrate responses with environmental data was difficult
because of the high variability in the environmental data. However, it was further complicated
by the mismatch in the level of replication between the two datasets. As a consequence of
this, the macroinvertebrate data had to be collapsed to a lower level for comparison with the
environmental data, resulting in a loss of natural variability and analytical power. Since only
the strongest treatment effects, which could be detected above the background "noise", were
detected and modelled against the environmental data, it is possible that other "cause" and
"effect" relationships may have been overlooked.
From these results, it is clear that many macroinvertebrate taxa are suitable for use as
bioindicators in in situ trials, but that criteria used for selection of test species should
definitely include more than just impact-sensitivity and abundance. However, there are
several aspects associated with the experimental set up of field-based protocols involving
caged macroinvertebrates that may limit their usefulness as a rapid and reliable bioassessment
tool, and need to be considered when designing and undertaking these kinds of trials. It is also
apparent that choice of endpoint can greatly influence conclusions, with detection of treatment
effects reported in this thesis varying greatly depending on which morphological endpoint
was examined.
This study clearly demonstrated that there may be significant difficulties in establishing
causal relationships between environmental data and biotic responses of macroinvertebrates
deployed under field conditions. However, it has also shown that deployment of caged
macroinvertebrates in situ may assist in the determination of biological effects arising from
impaired water quality, which can then serve as the basis for more focussed laboratory or
mesocosm studies in which environmental conditions can be more readily controlled or
monitored.
| Identifer | oai:union.ndltd.org:ADTP/203503 |
| Date | January 2008 |
| Creators | Oswald, Louisa Jane, n/a |
| Publisher | University of Canberra. Institute for Applied Ecology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Louisa Jane Oswald |
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