Environmental Engineering Reference
In-Depth Information
Ta b l e 3 . 2
Trophic Classification of Temperate Freshwater Lakes, Based on a Fixed Boundary System.
Trophic Category
Ultra-oligotrophic Oligotrophic Mesotrophic Eutrophic Hypertrophic
Nutrient concentration (
μ
gl
−
1
)
Total phosphorus (mean annual value)
<
4
4-10
10-35
35-100
>
100
Ortho-phosphate
a
<
2
2-5
5-100
>
100
DIN
a
<
>
10
10-30
30-100
100
Chlorophyll-
a
concentration (
μ
gl
−
1
)
Mean concentration in surface waters
<
1
1-2.5
2.5-8
8-25
>
25
Maximum concentration in surface waters
<
2.5
2.5-8
8-25
25-75
>
75
Total volume of planktonic algae
b
0.12
0.4
0.6-1.5
2.5-5
>
5
Secchi depth (m)
Mean annual value
>
12
12-6
6-3
3-1.5
<
1.5
Minimum annual value
>
6
>
3.0
3-1.5
1.5-0.7
<
0.7
Lakes are classified according to mean nutrient concentrations and phytoplankton productivity (shaded area). Boundary values are mainly
from the OECD classification system (OECD, 1982), with the exception of orthophosphate and dissolved inorganic nitrogen (DIN), which
are from Technical Standard Publication (1982).
a
Orthophosphate and DIN are measured as the mean surface water concentrations during the summer stagnation period.
b
Total volumes (% water) of planktonic algae are for Norwegian lakes, growth season mean values (Brettum, 1989).
3.1.4 Monitoring water quality: objectives
surface. Epilimnion concentrations of nitrates and
phosphates can fall to very low levels towards the
end of stratification (late summer), and the lake
could then be dominated by algae such as dinoflag-
ellates (e.g.
Ceratium
) and colonial blue-greens
(e.g.
Microcystis
) which are able to carry out diur-
nal migrations into the nutrient-rich hypolimnion.
Environmental monitoring of aquatic systems, par-
ticularly in relation to water quality, provides infor-
mation on:
Environmental impacts
-
changes in hydrology.
Changes in phytoplankton population can be used
to monitor major alterations in lake hydrology.
Inundation of floodplain lakes during periods of
high rainfall, for example, is characterised by
diatoms tolerant to water column mixing (e.g.
Cyclotella, Asterionella
) with the presence also of
coccoid green algae (e.g.
Schroederia, Kirchner-
iella
) associated with turbid and mixed conditions
(Stevic
etal
.,2013).Regressionofloodconditions
leads to water column stability, with increased phy-
toplankton biomass dominated by colonial blue-
green algae.
Classification of ecosystems in relation to water
quality, productivity and constituent organisms.
The most widely used classification (for both
lotic and lentic systems) is based on inor-
ganic nutrient concentrations, with division into
oligotrophic, mesotrophic and eutrophic systems
(Table 3.2). Detection and analysis of indicator
algae (Table 3.3) provides a quick indication of
trophic status and possible human contamination
of freshwater bodies.
Dynamics of nutrient and pollutant entry into
the aquatic system via point or diffuse loading
.
Localised or diffuse entry of contaminants can be
studied by analysis of benthic algal communities.
The potential use of these littoral algae in lakes,
Seasonal dynamics
. In temperate lakes these
include hydrological measurements (water flows,
residence time), thermal and chemical stratifica-
tion and changes in nutrient availability at the lake
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