Geoscience Reference
In-Depth Information
Table 4.3
Characteristic features in lakes of different trophic categories (Modified from OECD 1982; Håkanson & Jansson 1983.)
Trophic level
Primary production
Secchi
Chl-
a
Algal volume*
Total P†
Total N†
Dominant fish
(g C m
−
2
yr
−
1
)
(m)
(mg m
−
3
)
(g
−
3
)
(mg m
−
3
)
(mg m
−
3
)
Oligotrophic
<
30
>
5
<
2.5
<
0.8
<
10
<
350
Trout, whitefish
Mesotrophic
25-60
3-6
2-8
0.5-1.9
8-25
300-500
Whitefish, perch
Eutrophic
40-200
1-4
6-35
1.2-2.5
20-100
350-600
Perch, roach
Hypertrophic
130-600
0-2
30-400
2.1-20
>
80
>
600
Roach, bream
*Mean value for the growing period (May-October)
†Mean value for the spring circulation.
gL
−1
, in
mesotrophic systems from 1 up to 10, in eutro-
phic systems from 10 to 100, and in hypertrophic
systems the Chl values are generally higher than
100
(oligotrophic) lakes, the concentrations of total
phosphorus (TP; generally the key nutrient regu-
lating primary production in lakes) may vary
within a year from very low to high values.
A similar classification system is shown in
Fig. 4.1. It uses values of chlorophyll
a
(
values generally vary from 0.1 to 1
μ
gL
−1
. Thus, the boundary Chl values for
every trophic class can be set equal to a power
with the base 10.
A Trophic State Index (TSI) is defined
accordingly:
μ
gL
−1
)
as the basic criteria to classify lake trophic level
because chlorophyll (Chl) is relatively easy and
inexpensive to measure and it is a generally used
biological measure of phytoplankton biomass.
In oligotrophic systems the mean summer Chl
μ
TSI
=
25 · (log(Chl)
+
1)
HSI Colour (mg Pt L
−
1
)
1000
100
Hyperhumic
300
82
Polyhumic
66
100
Meso-
humic
48
30
Oligo-
humic
28
10
Ultraoligohumic
0
3
Oligotrophic
Mesotrophic
Eutrophic
Hypertrophic
1
.1
0
1
25
10
100
1000 Chlorophyll (
µ
g L
−
1
)
50
75
100 TSI
Fig. 4.1
The relationship between lake colour and humic state on the
y
axis and lake chlorophyll and trophic state on the
x
axis and
data from 936 lakes: HSI, Humic State Index; TSI, Trophic State Index. (Modified from Håkanson & Boulion 2002.)
