Sampling, Biomass Estimation and Counts of Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 91

Water surface

Microalga

Bacterium

Biofilm floc - observed
by phase-contrast
microscopy

Planktonic
phase

Figure 2.25 Experimental appr-
oaches to biofilm species enumer-
ation and biomass determination.
Hypothetical biofilm composed of
bacteria and algae embedded in extra-
cellular polymeric matrix (shaded).
The biofilm is in equilibrium with
a planktonic phase, which includes
bacteria, microalgae and globules of
detached matrix (flocs). Details of
biofilm structure not shown.

Total biomass
- carbohydrate level

BIOFILM Community composition

- Molecular analysis

Substratum

Bioilm structure
− Light and electron
Microscopy

1998), or may develop to produce dense growths of
attached filamentous algae (periphyton). Organisms
present in biofilms, such as algae and bacteria, are
also in dynamic equilibrium with surrounding plank-
tonic populations (Fig. 2.1) and detached floccules of
matrix(Fig.2.25)soanystudyofbioilmbiomassand
community change should also take these planktonic
constituents into account.
Submerged biofilms vary considerably in terms of
the development of carbohydrate matrix (Fig. 2.24),
with mucilaginous communities requiring spe-
cialised techniques of sampling, identification and
enumeration.

Algal biomass

The combined biomass of eukaryotic and prokary-
otic algae within biofilms is normally assessed as
chlorophyll- a content per unit area or per unit car-
bon, using laboratory extraction and pigment analy-
sis techniques outlined in Section 2.3.3. This can be
carried out directly on environmental samples or on
experimental biofilms.
Sutherland et al . (1998) used chlorophyll -a anal-
ysis to monitor algal biomass in estuarine diatom
biofilms, showing a significant positive correlation
with biofilm biomass measured as colloidal carbon
(biofilm matrix). Lyon and Ziegler (2009) analysed
algal biomass in epilithic biofilm communities of four
headwaterstreams(Arkansas,USA).Meanvaluesfor
total biofilm chlorophyll content ranged from 2.8 to
19.9 μgmg −1 (chlorophyll/carbon), directly relating
to stream trophic status and biofilm nitrogen content
(0.7-2.9% total mass).
With experimental biofilms, Jarvi et al. (2002)
studied an algal biofilm using artificial plastic sub-
strates placed on the river bed and within the water
column. Rates of algal biofilm production were deter-
mined as chlorophyll- a increase cm −2 day −2 . These
studies demonstrated a river algal biofilm bloom in
early spring, prior to peak suspended chlorophyll- a

2.9.1 Mucilaginous biofilms

Quantitative assessment of mucilaginous biofilms
can be considered in relation to biomass, commu-
nity composition and matrix structure (Fig. 2.25,
Table 2.8).

2.9.2 Biomass

Biofilm biomass includes organic matrix, inorganic
constituents plus the whole range of microorganisms
contained within the matrix - including algae.