4.3. Monitoring of lakes

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Surface water quality monitoring

4.3 Monitoring of lakes

Norway, Finland and Sweden have numerous lakes accounting for approximately 5-10 per cent of the surface area. A large number of lakes can also be found in Denmark, the northern part of Germany, Ireland and the northern and western parts of the United Kingdom. In central Europe most natural lakes are situated in mountain regions, the ones at high altitude being relatively small and the one in the valleys being the largest, examples being Lake Geneva, Lake Constance, Lake Garda and Lake Maggiore in the Alps. In addition, several lakes can be found in Austria and the northern parts of Greece. In Portugal, Spain, France, Belgium, The Netherlands, southern England, and the central parts of Germany there are generaly few natural lakes. In these areas man-made lakes such as reservoirs and ponds occur more frequently than natural lakes. In Spain, for instance, there are more than 1,000 large reservoirs.

Chemical and physical assessment of lake water quality

Only few countries in the EEA area have national monitoring programmes for assessment of the chemical and physical water quality of lakes. Some countries, however, undertake local monitoring of lakes, the German Federal States (Länder), for instance, monitor the environmental state of lakes in their respective areas. Local lake monitoring activities are generally not standardized at a national level, and the variables and sampling frequency vary. During the last 10-15 years some countries have made national lake inventories and collected data and elaborated reports on the general environmental state of lakes based on locally gathered information.

In the Nordic countries, in which there are many natural lakes, monitoring programmes cover a vast number of lakes. Finland, for instance, has been monitoring a wide range of lakes since the early 1960s. During the 1980s Norway and Swden have made lake surveys to assess the extent of acidification and eutrophication. Some countries have a long tradition for monitoring large nationally important lakes, Austria has by way of example monitored Lake Constance (AU-L1) and Neusiedler See since 1961 and 1972, respectively, and the Norwegian Lake Mjösa has been studied since 1971 (NO-L3). Several countries, for example the Netherlands and Portugal, do not have a specific lake monitoring programme, but include their lakes in river or inland water programmes.

In Table 4.3.1 13 general monitoring programmes aimed at chemical and physical assessment of lake water quality are listed. The main national lake monitoring programme of each country is listed first.

Network set-up and sampling frequency

The general national monitoring programmes can be divided into two categories. The "Survey-type" programme typically covers a great number of lakes that are sampled at long intervals. Examples of this type are NO-L2 and SE-L1, including around 100 lakes each. In Ireland a national lake survey (IE-L1) was performed in the period 1987-1990, including a total of 170 large lakes and some representative smaller lakes. Additionally, a remote sensing survey including 360 Irish lakes was performed in 1989-1990. More intensive monitoring programmes with a sampling frequency of several times a year (eg. DK-L1, SE-L3) typically cover a smaller number of lakes. Survey-type lake monitoring programmes provide a general description of the environmental state of a wide range of lakes, whereas more frequent monitoring provides information on dynamics and seasonal variation that may be used to detect trends.

Table 4.3.1: National lake monitoring programmes.

Country	Code	Lakes no.	Sites no.	Samp. freq.	No of determinands
Austria	no national lake monitoring programme¹
	AU-L1	1	6	12	28
	AU-L2	1	1	1	27
Belgium	no information
Denmark	DK-L1	37	40	19	20
Finland	FI-L1		71	3	28
	FI-L2		71	0.3	5
	FI-L3		u.k.	0.4	18
	FI-L4		176	1	24
France	no national lake monitoring programme²
Germany	no national lake monitoring programme³
Greece	no national lake monitoring programme⁴
Ireland⁵	IE-L1	170	Varying		13
	IE-L1	360	Remote sensing
Luxembourg	LU-L1	3	10	8	26
The Netherlands	no national lake monitoring programme⁶
Norway	NO-L1	355		4	21
	NO-L2	1005		0.1	14
	NO-L3	1	4	12	16
	NO-L4		50	1	21
Portugal	no national lake monitoring programme⁷
Spain⁸	ES-L1	350(reservoirs)		4
	ES-L2	496(reservoirs)		4
Sweden	SE-L1	1000		0.2	29
	SE-L2	85		4	31
	SE-L3	15		7	34
United Kingdom	no national lake monitoring programme⁹
	UK-L1/UK-L2¹⁰

^{1AU: Local monitoring of lakes. A
national monitoring programme is planned. ²FR: Local monitoring of lakes.

³GE: Local monitoring of lakes by Länder.

⁴GR: The inland surface monitoring programmes GR-R1 and GR-R2 include
also sampling of lakes, but the number of lakes and the analysis programme is unknown.

⁵IE: Past programmes. A new programme is in preparation.

⁶NL: The inland water monitoring programme R1 includes several large
lakes.

⁷PT: The inland water monitoring programme R1 includes several
reservoirs.

⁸ES: The R1 river monitoring programme includes a few reservoirs.

⁹UK: Local monitoring of lakes.

¹⁰ The purpose of the programmes is monitoring of toxic blue-green
algae.

Variables measured

A total of 85 variables are measured in the lake
monitoring programmes, but only 42 are represented in more than two programmes. In the
following we will mainly consider variables present in at least three monitoring
programmes. A brief overview of the main variables according to categories measured in
lake monitoring programmes is presented in Table 4.3.2.

Table 4.3.2: Chemical and
physical water quality variables measured in at least two lake monitoring programmes.
Mnemonic codes are given in parenthesis.

Basic

variables
Organic matter & oxygen conditions
Nutrients/ Eutrophication
Acidification
Specific ions

water
flow (Q);

water temperature (TEMPW);

pH (PH);

conductivity (COND);

dissolved oxygen (OX);

colour (CNR);

turbidity (TURB)
suspended
matter (SM);

turbidity (TURB);

Biological Oxygen Demand (BOD);

Chemical Oxygen Demand (COD);

Total Organic Carbon (TOC)

dissolved oxygen (OX);

ammoniacal nitrogen (NH4N)
total
phosphorus (PTOT);

dissolved reactive phosphate (PO4P);

total or Kjeldahl nitrogen (NTOT);

oxidized nitrogen (NO23N);

ammoniacal nitrogen (NH4N);

chlorophyll a (CHLA);

Secchi disc transparency (SDT)
See
section 4.4
chloride
(CL);

sulphate (SO4);

sodium (NA);

potassium (K);

calcium (CA);

magnesium (MG);

silica (SIO2);

Metals
Org. micropollutants
Microbiological
Biological organism

aluminium
(AL);

cadmium (CD);

chromium (CR);

copper (CU);

iron (FE);

mercury (HG);

manganese (MN);

nickel (NI);

lead (PB);

zinc (ZN)
see
section 4.6
total
coliform bacteria (COLITOT); faecal coliform bacteria (COLIFAEC); faecal streptococci
bacteria (STR_FAEC)
macroinvertebrates
(INVERT)

zoobenthos (INVERT)

phytobenthos (PHYTBEN)

phytoplankton (PHYTPL)

zooplankton (ZOOPL)

macrophytes (MAPHYT)

fish (FISH)

Basic variables

Variables describing the basic chemical and physical
properties of lake water are included in most programmes (Table 4.3.3). Generally, the
analysis programmes include measurement of water temperature (TEMPW), pH (PH), dissolved
oxygen (OX) and conductivity (COND), whereas colour (CNR), turbidity (TURB) and absorbance
(ABS) are only measured in a minority of programmes. Basic variables are missing in
FI-L2/L3. These programmes are specifically concerned with biological monitoring(-L2) and
monitoring of bioaccumulating compounds(-L3). Also NO-L1 (eutrophication) lacks the most
essential basic variables.

Table 4.3.3: Basic variables
measured in national lake monitoring programmes. For each monitoring programme the number
of annual samples are listed.

Country
Code
TEMPW
PH
COND
OX
CNR
TURB
ABS

Austria
AU-L1
12
12
12
12
.
.
.

AU-L2
5
1
1
5
5
.
.

Denmark
DK-L1
19
19
.
19
.
.
.

Finland
FI-L1
3
3
3
3
3
3
.

FI-L4
1
1
1
.
1
1
.

Ireland
IE-L1
X
X
X
X
X
.
.

Luxembourg
LU-L1
8
8
8
8
8
8
.

Norway
NO-L1
.
.
.
.
4
4
.

NO-L2
.
0.1
0.1
.
.
.
.

NO-L3
12
12
12
.
.
.
.

NO-L4
.
1
1
.
.
.
.

Sweden
SE-L1
0.2
0.2
0.2
0.2
.
.
0.2

SE-L2
4
4
4
4
.
.
4

SE-L3
7
7
7
7
.
.
7

Organic matter and oxygen conditions

Five summary variables as indicators for the
concentration of organic matter are measured in the various lake monitoring programmes:
Total Organic Carbon (TOC), Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand
(COD), suspended particulate solids (SM) and Turbidity (TURB).

Table 4.3.4: Summary variables for
organic matter, dissolved oxygen and ammonium measured in national lake monitoring
programmes. For each monitoring programme the number of annual samples are listed.

Country
Code
TOC
OX
BOD/COD
SM
TURB
NH4N

Austria
AU-L1
.
12
.
.
.
12

AU-L2
.
5
1
.
.
1

Denmark
DK-L1
.
19
19
19
.
19

Finland
FI-L1
3
.
3
.
3
3

FI-L4
1
.
1
.
1
1

Ireland
IE-L1
.
X
.
.
.
X

Luxembourg
LU-L1
.
8
8
.
8
8

Norway
NO-L1
4
.
.
.
4
.

NO-L2
0.1
.
.
.
.
.

NO-L3
12
.
.
.
.
.

NO-L4
1
.
.
.
.
.

Sweden
SE-L1
0.2
0.2
.
.
.
0.2

SE-L2
4
4
.
.

4

SE-L3
7
7
.
.

7

Nutrients/eutrophication

As trophic state is an important criterion for
evaluating the ecological condition of lakes, variables related hereto are commonly
measured in the various lake monitoring programmes. The variables can be divided into two
groups: nutrients (phosphorus and nitrogen), and variables describing the response to the
trophic state (Secchi disc transparency and chlorophyll a). Nearly all the lake monitoring
programmes include measurement of total phosphorus (PTOT), total nitrogen (NTOT), oxidized
nitrogen (NO23N) and chlorophyll a (CHLA). Measurement of dissolved reactive phosphate
(PO4P), ammonium nitrogen (NH4N) and Secchi disc transparency (SDT) is included in most of
the monitoring programmes. In the lake monitoring programmes with more than one annual
sample the sampling frequency of eutrophicatoin indicators varies from 3-4 annual samples
in the FI-L1, NO-L1 and SE-L2 monitoring programmes to 19 annual samples in the Danish
lake monitoring programme (DK-L1).

Table 4.3.5. Indicators of
eutrophication measured in national lake monitoring programmes. For each monitoring
programme the number of annual samples are listed.

Country
Code
PTOT
PO4P
NTOT
NH4N
NO23N
SDT
CHLA

Austria
AU-L1
12
12
12
12
12
.
12

AU-L2
5
5
.
1
5
5
5

Denmark
DK-L1
19
19
19
19
19
19
19

Finland
FI-L1
3
3
3
3
3
3
3

FI-L4
1
.
1
1
1
.
.

Ireland
IE-L1
X
X
.
X
X
X
X

Luxembourg
LU-L1
8
8
.
8
8
8
.

Norway
NO-L1
4
4
4
.
4
4
4

NO-L2
.
.
.
.
0.1
.
.

NO-L3
12
.
12
.
12
12
12

NO-L4
.
.
.
.
1
.
.

Sweden
SE-L1
0.2
0.2
0.2
0.2
0.2
0.2
0.2

SE-L2
4
4
4
4
4
4
4

SE-L3
7
7
7
7
7
7
7

Specific major ions

Many of the lake monitoring programmes include
measurement of the major cations: calcium (CA), magnesium (MG), sodium (NA) and potassium
(K), and the major anions: sulphate (SO4) and chloride (CL). Silica (SiO2) is also
measured in several lake monitoring programmes.

Table 4.3.6: Major specific ions
measured in national lake monitoring programmes. For each monitoring programme the number
of annual samples are listed.

Country
Code
CA
MG
NA
K
SIO2
SO4
CL

Austria
AU-L1
12
12
12
12
12
.
12

AU-L2
1
1
1
.
.
1
1

Denmark
DK-L1
.
.
.
.
19
.
.

Finland
FI-L1
3
3
3
3
3
3
3

FI-L4
1
1
1
1
1
1
1

Ireland
IE-L1
X
X
X
X
X
X
X

Luxembourg
LU-L1
8
8
8
8
.
8
8

Norway
NO-L1
4
4
4
4
.
4
4

NO-L2
0.1
0.1
0.1
0.1
.
0.1
0.1

NO-L3
.
.
.
.
12
.
.

NO-L4
1
1
1
1
.
1
1

Sweden
SE-L1
0.2
0.2
0.2
0.2
0.2
0.2
0.2

SE-L2
4
4
4
4
4
4
4

SE-L3
7
7
7
7
7
7
7

Metals

Up to ten metals are measured in the various
national lake monitoring programmes. Some monitoring programmes include only determination
of very few metals such as, for instance, iron (FE) in the Danish lake monitoring
programme (DK-L1), while the Swedish and Finnish lake monitoring programmes include
measurement of several metals: iron, manganese (MN), aluminium (AL), cadmium (CD),
chromium (CR), copper (CU), mercury (HG), lead (PB) and zinc (ZN).

Table 4.3.7: Metals measured in national
lake monitoring programmes. For each monitoring programme and variable the number of
annual samples are listed.

Country
Code
FE
MN
AL
CD
CR
CU
HG
PB
ZN

Austria
AU-L1
12
12
.
.
.
.
.
.
.

Denmark
DK-L1
19
.
.
.
.
.
.
.
.

Finland
FI-L1
3
3
3
.
.
.
.
.
.

FI-L3
.
0.4
.
0.4
0.4
0.4
0.4
0.4
0.4

FI-L4
1
1
1
.
.
.
.
.
.

Norway
NO-L2
.
.
0.1
.
.
.
.
.
.

NO-L4
.
.
1
.
.
1
.
.
.

Sweden
SE-L1
0.2
0.2
0.2
0.1
.
0.1
0.1
0.1
0.1

SE-L2
4
4
4
4
.
4
4
4
4

SE-L3
7
7
7
7
.
7
7
7
7

Biological assessment of lake water quality

Biological variables are direct indicators of
environmental quality. While chemical and physical assessment measures variables decisive
for environmental quality, biological assessment gives a direct description of the
ecological impact. For instance, biological variables are important in the assessment of
water quality with respect to eutrophication and acidification.

Biological variables are part of the sampling
routine of many general lake monitoring programmes (DK-L1, NO-L1/L2, SE-L1/L2/L3) as well
as programmes concerning specific localities (AU-L1/L2, NO-L3). The Finnish FI-L2
programme only includes biological variables. There are several ways of expressing
biological variables. A phytoplankton community, for instance, may be expressed as a
species list (qualitatively), or as biomass, biovolumes and cell counts (quantitatively).
Furthermore, there may be differences in taxonomic resolution (species level, family
level). Sampling and investigation of phytoplankton (PHYTPL) and zooplankton (ZOOPL) are
components of several monitoring programmes. Apart from a general evaluation of the
phytoplankton community, the objectives of some programmes are more specific such as
assessment of the occurrence of potentially toxic blue-green algae in waterbodies used for
bathing or drinking water supply (eg. UK-L1). Bottom fauna (INVERT), macrophytes (MAPHYT)
and fish fauna (FISH) are also objects of study in some of the lake monitoring programmes.

Table 4.3.8: Biological organisms
studied in national lake monitoring programmes. For each monitoring programme and variable
the number of annual samples are listed.

Country
Code
PHYTPL
ZOOPL
INVERT
MAPHYT
FISH

Austria
AU-L1
12
12
.
.
.

AU-L2
5
5
.
5
.

Denmark
DK-L1
19
19
.
1
0.2

Finland
FI-L2
0.33
0.33
0.33
.
.

Ireland
IE-L1
X
X
.
.
.

Norway
NO-L1
4
4
.
.
4

NO-L2
.
.
0.1
.
0.1

NO-L3
12
12
12
.
.

Sweden
SE-L1
.
.
0.2
.
.

SE-L2
1
.
1
.
.

SE-L3
6
1
1
0.3
1

Measurement of specific constituents of sediment and
biota

In addition to monitoring of lake water quality and
ecological state it may be relevant to examine the concentrations of various elements in
sediment or living organisms, especially when dealing with pollution variables such as
heavy metals and organic micropollutants, but also when dealing with eutrophication
problems data on sediment nutrient contents is important. The most commonly measured
metals are mercury, cadmium, lead, chromium, copper, nickel and zinc.

The following monitoring programmes include analyses
of substances in sediment or biota:

DK-L1: Nutrients in sediment (every 5th year).

FI-L3: Metals and organic micropollutants in sediment, fish and clams.

NO-L4: Metals in sediment (yearly).

NO-L5: Survey of metals in sediment and mercury in fish (1986-1991).

SE-L2: Metals and nutrients in sediment (every 10th yr).

Mercury in fish (every 3rd yr).

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