Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 127

Ta b l e 3 . 1 0 Benthic Diatom Community Analysis of Finnish Rivers Showing Some of the Major Community Groups.

Group Ecoregion Stream water quality Characteristic taxa

A Eastern Finland Polyhumic, acid Eunotia rhomboidea

Eunotia exigua

B Eastern Finland, woodland Oligotrophic, neutral Fragilaria construens,

Gomphonema exilissimum

C South Finland, small forest

streams

Slightly acid, low conductivity,
humic

Gomphonema gracile
Achnanthes linearis

D South Finland Connect

lakes

Aulacoseira italica a
Rhizosolenia longiseta a

E Mid-boreal Mesotrophic, neutral, humic Achnanthes bioretii

Aulacoseira subarctica

F North boreal Oligotrophic, clear water, neutral Caloneis tenuis

Gomphonema clavatum

H Arctic-alpine Achnanthes kryophila

Eunotia arcus

J South Finland, many small

lakes and ponds

Polluted: Eutrophic, high organic
content

Aulacoseira ambigua a
Cyclotella meneghiniana a

K South Finland Polluted: Eutrophic - treated

sewage, diffuse agricultural
loading

Motile biraphid species - e.g.
Surirella brebissonii
Nitzschia pusilla

Source : Soininen et al ., 2004. Reproduced with permission from John Wiley and Sons Ltd.
a Planktonic diatoms. Groups A-K selected from 13 ecoregions.

either in terms of change from an original state or in
relation to specific human effects.

is liable to disturbance by water flow and the oxy-
genated conditions minimise preservation of biolog-
ical material.
An alternative strategy, in the quest for a baseline
state, is to locate an equivalent ecological site that has
a natural original community - unaffected by human
activity. This is not straightforward, however, since
local variations in environment and species within a
particular ecoregion make it difficult to define what is
actually meant by a natural original community. This
is evident in the studies of Eloranta and Soininen
(2002) on Finnish rivers, for example, where diatom
species composition of undisturbed benthic commu-
nities varied with river substrate, turbidity and local
hydrology (Table 3.11).
In an objective assessment of human impact on
natural communities, Tison et al . (2005) analysed
836 diatom samples from sites throughout the French
hydrosystem using an unsupervised neural network,
the self-organising map. In total, 11 different
communities were identified, 5 corresponding to

Change from a 'natural' community

The use of benthic diatom populations to assess
anthropogenic impacts on water quality implies com-
parison of current conditions to a natural original
community, with deviation from this due to human
activities such as eutrophication, toxic pollution and
changes in hydrology. This concept is implicit in
some major research programmes, such as the Euro-
pean Council Water Framework Directive (WFD:
European Union, 2000) where the baseline is referred
to as 'reference conditions'. In the case of lakes
(Section 3.2.2), reference conditions can be deter-
mined by on-site extrapolation into the past using
sediment analysis. Diatom sediment analysis is not
generally appropriate for rivers, however, since there
is little sedimentation of phytoplankton, the sediment