Effects of Toxic Chemicals and Other Pollutants on Aquatic Ecosystems - Freshwater Ecology: Concepts and Environmental Applications - page 279

0

~1975

5

~1950

10

~1920

15

~1880

20

25

30

35

048 020 080

020 024 4567

Inferred pH

023
Relative abundance (%)

FIGURE 14.9 Distribution of Mallomonas spp. scales (a chrysophyte) with depth and recon-
structed pH from Big Moose Lake (New York). Sediments were dated by 210 Pb content (from
Majewski and Cumming, 1999, with kind permission from Kluwer Academic Publishers).

these blooms collapse, the resulting O 2 depletion can have negative impacts
on animals (Turner et al., 1995). Diversity of planktonic and benthic algae
decreases with lower pH (Dickman and Rao, 1989). Similar decreases in
algal diversity and replacement with filamentous green algae have been
documented for acidified streams (Meegan and Perry, 1996).
Shifts in algal communities in lake sediment cores resulting from pH
changes have been used to verify historical trends in acidification (Mallory
et al., 1998). Such verification is required before politicians are willing to
enact stringent and potentially costly emission controls. In this technique,
existing lakes are used to create an index that correlates algal communities
with pH. This index is then used to infer pH from species with parts that
are well preserved in the sediment, such as diatom frustules or chryso-
phytes scales. Sediment cores can be used to establish changes in the com-
munity over time. The deeper in the sediments, the longer ago the algae
were deposited. When the index is coupled with isotope analysis to date
specific depths of sediments, it yields a record of pH in a lake over time
(Fig. 14.9). In the case of Big Moose Lake, New York, some chrysophyte
species are dominant in low pH, whereas others are found only at the
higher pH values associated with preindustrial conditions.
Diversity of plants and animals also decreases as aquatic systems be-
come more acidic. Macrophyte diversity is lower in low pH lakes and fun-
gal diversity is less in acidic streams (Fig. 14.10). Macrophyte communi-
ties become less diverse as streams acidify (Thiébaut and Muller, 1999).
Invertebrates exhibit a wide range of acid sensitivities. Perhaps the most