Science Education News (SEN) Journal 2017 Volume 66 Number 4 December 2017 | Page 44

GENERAL ARTICLES
Swimming in Sand – Frogs and Sand-Mining at Smiths Lake (continued)
The effects of habitat change on the frog
community composition How has sand-mining changed the local
environment?
In the swamp the chance of finding a frog was significantly
decreased following the cessation of mining, with more frog
species found before and during mining. This was likely due to
increasing salinity, which is also suspected to have reduced the
occurrence of all frog species. Despite large changes in aquatic
plant cover and salinity, there were no significant effects of these
measures on swamp community composition. There were no
significant effects of any of our measures on the presence or
absence of frog species at the Dune Pond Site. As the recovery of many animal species from the impacts of sand-
mining appears to be dependent on the successful recovery of
the vegetation beforehand, it remains to be determined exactly
what impacts were generated by sand-mining, and how these
impacts have affected off-site ecosystems. In an assessment of
the impacts of mining in general on native ecosystems, Andersen
et al. (2014) concluded that there were three main impact types to
be considered: immediate impacts (e.g. land-clearing, changes
to topography, changes to hydrology, changes to soil chemistry,
introduced pollutants, noise and disturbance); collateral impacts
(these occur off-site and include changes to local flora and fauna
associated with changing habitats, soil chemistry and hydrology),
and long-term impacts (these arise because the site cannot be
fully rehabilitated or because the disruption due to mining was so
great that original species have been lost).
Discussion
Are there any Trends in the Data?
While it is evident that there have been major habitat changes
as a result of mining in the areas adjoining the mine path, the
responses of individual frog species were not uniform. It is evident
from this study that frog communities in both the Dune Pond and
Swamp Sites were greatly affected by the nearby mine, and that
mining-related impacts significantly altered the composition of
the impacted frog communities. The response of different frog
species present was also quite diverse. For example, four frog
species (Litoria aurea, Adelotus brevis (Fig. 13), Limnodynastes
tasmaniensis and Pseudophryne bibronii) disappeared from the
dune or swamp sites, one frog species (Crinia tinnula) appeared
and became relatively common post-mining, and several species
underwent major changes in abundance during and after mining.
For both the dune and swamp site, the average number of frogs
30 years post-mining is well less than the average number of
species present before the onset of mining.
At Bridge Hill two major environmental changes were recorded
by this study: (1) earthworks associated with sand mining, and
(2) land clearing that mobilised large amounts of salt and calcium
carbonate. Once exposed, these water-soluble compounds were
quickly flushed into the nearby pond and swamp environments.
Salinity levels quadrupled in both the pond and swamp sites and
remained at these levels for almost 15 years after sand-mining
ceased. Salinity has been slowly falling since, but average salinity
in the dune and swamp sites 34 years after the cessation of
sand-mining are still approximately twice the levels experienced
before sand-mining.
The release of calcium carbonate from remnant shells or lime
debris in the dune raised the pH of the water in the dune pond
and swamp almost immediately when mining commenced. The
pH of the dune pond ranged between 6.4 and 6.8 pre-mining,
but jumped to 8.4 during the mining phase. The swamp site was
originally more acidic with pHs of between 5.4 and 5.8 being
recorded pre-mining. pH rapidly rose in the swamp water with
the onset of mining and peaked at 8.4 during mining. The pH of
the water in both the dune pond and the swamp has slowly fallen
over the years but both are still substantially different from pre-
mining levels.
The impact of a sustained flush of salty, alkaline water into
the dune pond and swamp site caused a sudden and severe
change to the water chemistry of the nearby wetland sites. These
changes were most likely responsible for the changes in aquatic
vegetation that followed in both sites. Frog communities are likely
to have responded to both the changes in water chemistry as well
as the changes to vegetation, although our statistical analyses
only found evidence of increasing pH reducing frog occurrence
in the swamp site.
Figure 13: Tusked Frog- a species that was seriously impacted
by sand mining. Image A. White.
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SCIENCE EDUCATIONAL NEWS VOL 66 NO 4