Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 107

Conservation assessment . Analysis of freshwater
algae has become an important part of the survey
and data collection programme used in the evalua-
tion of lakes for their nature conservation value
(Duker and Palmer, 2009). Evaluation of water
quality is also important for existing conserva-
tion sites. In the United Kingdom, a large number
of freshwater Sites of Special Scientific Interest
(SSSIs) are believed to be affected by eutrophica-
tion (Nature Conservancy Council, 1991; Carvalho
and Moss, 1995). In case of lakes, the role of algal
bioindicators in this assessment is based on both
contemporary organisms (Section 3.2.1) and fossil
diatoms within sediments (Section 3.2.2).

Malawi (Africa: 4-9 My) and Baikal (Russia: 25-
30 My). Long-term evolution within these inde-
pendent and enclosed aquatic systems has led
to the generation of high proportions of unique
species (endemism), with over 50% endemic
fauna and flora in lakes Tanganyika and Baikal
(Martens, 1997). The presence of substantial levels
of endemism in these large water bodies, together
with the fact that even non-endemic species may
have unique adaptations, means that conventional
bioindices will need to be adjusted to suit particular
situations.

3.2.1 Contemporary planktonic and attached algae as
bioindicators

3.2 Lakes

Bothplanktonicalgae(presentinthemainwaterbody
of the lake - pelagic zone) and attached algae (occur-
ring around the edge of the lake - littoral zone) have
been used to monitor water quality (Fig. 3.2).

The use of algae as bioindicators of water quality
is influenced by the long-term retention of water in
lake systems and also by the age of the lake. Reten-
tion of water can be quantified as 'water retention
time' (WRT), which is the average time that would
be taken to refill a lake basin with water if it were
emptied. WRT for most lakes and reservoirs is about
1-10 years, but some of the world's largest lakes have
values far in excess of this - including extreme values
of 6000 and 1225 years for lakes Tanganyika (Africa)
and Malawi (Africa), respectively.
Characteristics of lake hydrology and age result in:

Phytoplankton: general water quality

Most studies on lakes (see Section 3.2.3) have used
the phytoplankton (rather than benthic) community
for contemporary environmental assessment, since
it is the main algal biomass, is readily sampled at
sites across the lake and many planktonic species
have defined ecological preferences. Analysis of the
phytoplankton community from a number of sites
across the lake also provides information on aquatic
conditions in general and is the basis of broad
categorisation of lakes in relation to water quality,
particularly trophic state (Table 3.3).

Phytoplankton dominance . In moderate- to high-
nutrient deep lakes, phytoplankton populations are
able to grow and are retained by the system (not
flushed out). Their dominance over non-planktonic
algae and macrophytes means they are routinely
used as bioindicators.

Attached algae: ecological status and localised
water quality

Long-termexposure . In many lakes, planktonic and
benthic algae have relatively long-term exposure to
particular conditions of water quality and relate to
specific chemical and physical characteristics over
extended periods of time (weeks to years).

Although there have been relatively few studies using
attached (benthic and epiphytic) algae to assess water
quality, analysis of non-planktonic (mainly littoral)
algae can provide useful information on general ecol-
ogy and local water quality.

Endemicspecies . Some of the world's largest lakes
have existed over a long period of time - including
lakes Tanganyika (Africa: 2-3 Million years),

General ecological status As well as plank-
tonic algae, attached algae can also be important