Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 128

Ta b l e 3 . 1 1 Diatom Adaptations to Local Environmental Conditions in Finnish Rivers.

Environment Typical diatoms

Substrate
Hard substrates Attached epilithic and epiphytic taxa

Soft substrates Pinnularia , Navicula and Nitzschia

Turbidity
Clear waters Achnanthes

Clay-turbid waters Surirella ovalis , Melosira varians and Navicula spp.

Hydrology
Lake and pond inflows

Aulacoseira spp., Cyclotella spp. and Diatoma tenuis

Source : Eloranta & Soininen, 2002. Reproduced with permission from John Wiley and Sons Ltd.

natural (undisturbed) conditions and relating to 5
different ecoregions (i.e. river types with similar
altitude range and geological characteristics). The
six other communities were typical of rivers that had
been disturbed by human activity. Although natural
variability occurred within individual ecoregions
(similar to that noted in Finnish rivers, see above),
this was greatly exceeded by the effects of pollution
at the different sampling sites. The study aimed
to identify diatom indicators for different types of
anthropogenic disturbance by comparing benthic
diatom communities in natural and disturbed sites.

3.4.5 Calculation of diatom indices

As with lake phytoplankton analyses (Section 3.2.3),
the benefit of river diatom indices is that they reduce
complex multi-species communities to single numer-
ical values. These provide a very simple quantitative
evaluation that can be appreciated and used by biol-
ogists and non-biologists alike.
In some cases, river diatom indices have been
determined that take into account all recorded
species. Stenger-Kovacs et al. (2014), for example,
analysed the biodiversity of benthic diatoms in Hun-
garian rivers in terms of Shannon index and species
evenness. Clear correlations occurred between
species number, biodiversity and stream category
(based on water chemistry and hydromorphology).
In other cases, analysis has been based on particu-
lar bioindicator algae, using either single or multiple
taxon assessments.

Use of bioindicators

Analternativeapproachtoanalysinghumanimpactin
terms of general disturbance is to use diatom indices
with indicator species that directly reflect particular
environmental changes resulting from human activi-
ties. Individual species can be numerically weighted
to reflect their degree of environmental specificity.
Bioindicators may relate to single parameters such
as total-P (Trophic diatom index - TDI - e.g.
Hofman, 1996) or reflect more general aspects of
water quality, combining organic loading and inor-
ganic nutrient concentration (IPS: index of pollu-
tion sensitivity, GDI: generic diatom index). Diatom
indicator lists for other variables such as salinity,
trophy, nitrogen metabolism types, pH and oxygen
requirements have also been published (van Dam
et al ., 1994).

Single taxon assessment

Indices based on a single species represent a very
simple environmental approach.
Kothe's index This is referred to as the 'species
deficiency index' ( F ) and relates the number of cells
( N 1 ) of a particular key species at site 1 to the number
( N x ) at site x , where:
F = N 1 − N x
N 1

× 100 (3.1)