Introduction to Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 3

Carbon fixed (mg C m -3 h -1 )

10 -1 10 2 10 3 1 10

(a) Highly eutrophic

(b) Eutrophic

10

(c) Mesotrophic

Figure 1.1 Examples of algal pri-
mary production in lakes of differ-
ent trophic status, showing how rates
of production typically change with
depth. Examples of each lake type
include (a) highly eutrophic; Lake
George(Uganda).(b)eutrophic;Blel-
ham Tarn (English Lake District),
Clear Lake (USA), Erken (Sweden).
(c) mesotrophic; Grasmere (English
Lake District), Castle Lake (USA).
(d) oligotrophic; Lake Tahoe (USA),
LakeBaikalinpart(Russia),Wastwa-
ter (English Lake District). Adapted
from Horne and Goldman (1994)

Approximate areal values
mg C m -2 h -1
George 380
Clear 116
Castle 70
Baikal 60
Tahoe 0.6

20

(d) Oligotrophic

50

(otherwise they flush out of the system) and ade-
quate light levels, so they tend to predominate at
the surface of lakes and slow-moving rivers. Ben-
thic algae require adequate light (shallow waters)
and can tolerate high rates of water flow, so pre-
dominate over phytoplankton in fast-flowing rivers
and streams. Benthic algae also require adequate
attachment sites - which include inorganic sub-
strate, submerged water plants and emergent water
plants at the edge of the water body. The distinc-
tion between planktonic and non-planktonic algae
is ecologically important and is also relevant to
algal sampling and enumeration procedures (see
Chapter 2).

Planktonic algae

Planktonic algae dominate the main water body of
standing waters, occurring as a defined seasonal suc-
cession of species in temperate lakes. The tempo-
ral sequence depends on lake trophic status (see
Section 3.2.3; Table 3.3) with algae forming dense
blooms in eutrophic lakes of diatoms (Fig. 1.16),
colonial blue-green algae (Fig. 1.5) and late popula-
tions of dinoflagellates (Fig. 1.10). During the annual
cycle, phytoplankton blooms correspond to peaks in
algal biovolume and chlorophyll -a concentration and
troughs in 'Secchi depth' - the inverse of turbidity
(Fig. 2.8).