Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 115

Ta b l e 3 . 4 Lake Trophic Indices.

Index Calculation Result Reference

(a) Major taxonomic groups: numbers of species
Chlorophycean index

<

Chlorococcales spp. / Desmidiales spp. 1 = oligotrophy Thunmark (1945)

> 1 = eutrophy

Myxophycean index Cyanophyta spp. / Desmidiales < 1 = oligotrophy Nygaard (1949)

> 1 = eutrophy

Diatom index Centrales spp ./ Pennales

Euglenophycean index Euglenophyta /

Cyanophyta + Chlorophyta

A/C diatom index Araphid pennate/Centric diatom spp. < 1 = oligotrophy

> 2 = eutrophy

Stockner (1972)

Compound index Cyanophyta + Chlorococcales +

Centrales + Euglenophyta spp. /
Desmidiales spp.

< 1 = oligotrophy
1-3 = mesotrophy

Nygaard (1949)

(b) Indicator algae: species counts or biovolumes
Species counts

Eutrophic spp./Oligotrophic spp. < 8 = oligotrophy Heinonen (1980)

Species biovolumes Eutrophic spp./Oligotrophic spp. < 35 = oligotrophy

(c) Indicator algae: species given weighted scores
Trophic index I L = ∑ ( fI S )∕ ∑ f 10-100, high

values indicate
higher pollution

Hornstrom (1981)

I T = ∑ (ν I S )∕ ∑ ν Trophic index—biovolumes Index values for

each trophic level

Brettum (1989)

Hornstrom's index : I L, trophic index of lake; f , species frequency on a 5 ◦ scale; I s, trophic index of species; Brettum's index : I T , index
of trophic level T; v , volume of species per litre; I s, trophic index of species.

expressedasbioticindicestocharacteriselaketrophic
status (Willen, 2000). These indices occur at three
levels of complexity (Table 3.4).

Although such indices provided useful infor-
mation (see below), they tended to lack environ-
mental resolution since many algal classes turn
out to be heterogeneous - containing species typ-
ical of oligo- and eutrophic lakes. Problems were
also encountered in some of the early studies with
sampling procedures, where net collection of algae
resulted in loss of small-sized (single cells or small
colonies) species. Such algae are often dominating
elements in the plankton community, and their loss
from the sample meant that the index was not rep-
resentative.
Example: The A/C diatom index of Stock-
ner (1972). The ratio of araphid pennate/centric
diatoms (A/C ratio) provides a good example of
the successful use of a broad taxonomic index in
a particular lake situation. Studies by Byron and

Indices based on major taxonomic groups .Early
phytoplankton indices (Table 3.4a) used major tax-
onomic groups that were considered typical of
oligotrophic (particularly desmids) or eutrophic
(chlorococcales, blue-greens, euglenoids) condi-
tion. The proportions of eutrophic/oligotrophic
species generated a simple ratio which could be
used to designate trophic status. Using the chloro-
phycean index of Thunmark (1945), for example,
counts of chlorococcalean and desmid species can
be expressed as a ratio, which indicates trophic
status over the range oligotrophy (

< 1) to eutrophy

( > 1).