In Finland, as in other member countries of the European Union, preparations for implementing the EC Water Framework Directive (WFD) have begun. The article describes the current monitoring and classification strategies for Finnish Lakes

Mittikka, Sari

English

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MONITORING AND CLASSIFICATION OF LAKES IN FINLAND 29 
MONITORING AND CLASSIFICATION OF LAKES IN FINLAND 
SARI MITIKKA 
(Dr S. Mitikka (S. Antikainen), 
Finnish Environment Institute (FEI), FIN-00251 Helsinki, Finland.) 
[Email: Sari.Mitikka@yyh.fi] 
Introduction 
In Finland, as in other member countries of the European Union, 
preparations for implementing the EC Water Framework Directive (WFD) 
have begun. Organisation of these preparations is described in the 
following article by Maunula et al. (pp. 33-38). Here I briefly describe the 
current monitoring and classification strategies for Finnish lakes. 
Lakes in Finland 
In Finland, there are about 5600 lakes with surface areas larger than 0.01 
km2, about 4500 larger than 0.5 km2 and 47 that are larger than 100 km2 
(Raatikainen & Kuusisto 1990). About 81% are lowland lakes, i.e. less 
than 200 metres above sea level. Mean depths are known for only for about 
800 lakes. Total lake area is about 33,350 km2 and approximation for total 
volume is 235.2 km3 (Kuusisto 1992). Estimated mean depth is then 7 
metres. Lakes are typically dimictic, i.e. temperature stratification of the 
water column occurs twice each year: in winter, under ice, and again in 
summer. Ice-cover in the winter lasts for three to five months. In central 
and eastern parts of the country, lakes typically form chains, i.e. several 
basins are connected to each other by straits. This complex mosaic of land 
and water, formed by glacial activity, is a unique feature of Finland. 
Monitoring 
Hydrological monitoring began as early as the 1840s, and a complete 
national coverage for monitoring water levels was achieved in 1911. The 
local pollution control of waters receiving waste-waters started in 1961 and 
was followed by national water quality monitoring in 1965. In the 1990s, 
data was collected from 71 national lake sites and c. 1700 sites belonging to 
local pollution control. In addition, regional monitoring was performed in 
areas where national or local sites were rare. The Finnish Lake Survey has 
been carried out twice, in the autumns of 1987 and 1995 (Mannio et al. 
2000), as part of the Nordic lake Survey (Henriksen et al. 1998). In this 
survey, lakes were selected using stratified random sampling from the 
30 SARI MITIKKA 
entire population of lakes (surface area > 0.04 km ), with unequal sampling 
fractions from the national lake database. All physico-chemical and 
hydrological data of the above-mentioned monitoring programmes are 
stored to common databases of the Finnish Environment Institute and 13 
Regional Environmental Centres. Biological data concerning local 
pollution control (mainly bottom fauna, fish and phytoplankton) are stored 
by private laboratories that carry out the monitoring. 
Eurowaternet 
Monitoring network design is currently being harmonized among the 
member states of the European Union. In Finland, 253 lake sites were 
included in the so-called Eurowaternet at the beginning of 2000 (Niemi et 
al. 2001 a,b). The 253 sites were selected as a sub-sample from regional and 
local networks; all 71 national monitoring sites were included. The site 
types comprise the following: 50 large lakes - all lake basins with surface 
areas greater than 100 km2 are included; 105 representative sites - lakes 
with typical water quality in the watercourse; 33 reference sites - at least 
90% of the catchment area of the lake is undisturbed; 48 impact sites 
from the local pollution control network; 17 small lakes impacted by 
agriculture. The programme for monitoring acidification (170 sites) will 
also continue. 
The total surface area of the lakes included above covers 61% of the 
total surface area of Finnish lakes. The proportion represented by lakes less 
than 10 km2 in area is relatively small, but they occur in large numbers 
(15,397 lakes in Finland have surface areas between 0.1 and 10 km). 
Therefore the Finnish Lake Survey should be repeated regularly, e.g. every 
10 years, in order to assess the state of small lakes. 
There are some 20 physico-chemical variables in the monitoring 
programme of Eurowaternet. Phytoplankton will be sampled every three 
years (in July) in all of the 253 sites mentioned above. However, in 15 of 
these sites our intensive programme of sampling phytoplankton (samples 
taken six times each year) is continuing, and macroinvertebrates are 
sampled in autumn. Macroinvertebrates are also monitored at about 200 
lake stations for local pollution control and these usually are sampled every 
three or five years. 
Classification of Finnish lakes 
An overview of the state of Finnish surface waters is based on the index of 
general water quality (Vuoristo 1998). Waters are divided into five classes 
on the basis of oxygen content, colour, turbidity, transparency, nutrients, 
MONITORING AND CLASSIFICATION OF LAKES IN FINLAND 31 
hygienic indicator bacteria, chlorophyll-α, algal blooms and toxic 
compounds. This classification describes the suitability of waters for water 
supply, fishing and recreational activities. According to the most recent 
survey, concerning the period 1994 to 1997, 38% of total lake area in 
Finland was classified as excellent, 42% as good, 16% as satisfactory and 
4% as poor (Antikainen et al. 2000). This information is based on data 
from nearly 5000 lake monitoring sites covering the whole country. Nearly 
93% of lakes larger than 1 km were included. In addition, rivers wider 
than 2 metres and the whole coastal sea area were classified. 
Finnish lakes are mainly polluted by diffuse loading from agriculture or 
forestry, and point-source loading from the pulp and paper industry and 
municipal wastewaters. The improvement of the quality of waters affected 
particularly by wastewaters from the pulp and paper industry, which began 
during the 1980s, has continued. The impact of diffuse loading on water 
quality has accentuated whereas that of point-source loading has decreased. 
This can be seen particularly in small lakes and rivers affected by 
agriculture and forestry. 
Implementing the WFD 
Preparing for implementation of the WFD has started in Finland under two 
ministries, the Ministry of Environment and the Ministry of Agriculture 
and Forestry. There is also an expert group for ecological classification. 
The catchment area of the River Vuoksi is our pilot area for discriminating 
lakes into types. Our largest lake, Lake Saimaa (4380 km"), is in that area. 
The River Vuoksi discharges to Lake Ladoga in Russia. 
We have started to test systems A and B of the WFD. We must consider 
the high content of humic substances in our dystrophic lakes. The mosaic 
complex of land and water makes it very difficult to separate different lake 
basins and discriminate them into types. It seems obvious that trophic 
levels assessed with phosphorus concentrations and dystrophy with colour 
are the most important factors in characterisation. Nevertheless other 
factors should also be taken into account when typing lakes, such as 
morphology (e.g. development of shoreline and size), and thermal stability 
- is there one period of stratification in summer (monomictic lakes) or a 
second period in winter (dimictic lakes). 
References 
Antikainen, S., Joukola, M. & Vuoristo, H. (2000). Suomen pintavesien 
laatu 1990-luvun puolivailissa (Water quality in Finland in the mid-
32 SARI MITIKKA 
1990s ). Vesitalous 2/2000. (In Finnish with English abstract). [See also 
http://www.vyh.fi/tila/vesi/laatu/map9497.html. 
Henriksen, A., Skjelvale, B. L., Mannio, J., Wilander, A., Harriman, R., 
Curtis, C, Jensen, J. P., Fjeld, E. & Moiseenko, T. (1998). Northern 
European Lake Survey, 1995. Ambio 27, 80-91. 
Kuusisto, E. (1992). The volume of the Lakes in Finland. (In Finnish with 
English abstract). Terra 104, 3-10. 
Mannio, J., Räike, A. & Vuorenmaa, J. (2000). Finnish lake survey 1995: 
regional characteristics of lake chemistry. Verhandlungen internatinale 
Vereinigung fur theoretische unci angewandte Limnologie 27, 362-367. 
Niemi, J., Heinonen, P., Mitikka, S., Vuoristo, H., Pietiläinen, O.-P., 
Puupponen, M. & Rönkä, E. (Eds) (2001a). The Finnish Eurowaternet -
with information about Finnish water resources and monitoring 
strategies. The Finnish Environment No.455, Finnish Environment 
Institute. [Available also at 
http://www.vyh.fi/eng/orginfo/publica/electro/fe445/fe455.htm]. 
Niemi, J., Heinonen, P., Mitikka, S., Vuoristo, H., Pietiläinen, O.-P., 
Puupponen, M. & Ränkä, E. (2001b). The Finnish Eurowaternet. 
European Water Management (August issue). 
Raatikainen, M. & Kuusisto, E. (1990). The number and surface area of the 
lakes in Finland. (In Finnish with English abstract). Terra 102, 97-110. 
Vuoristo, H. (1998). Water quality classification of Finnish inland waters. 
European Water Management 1, 35-41. 


Monitoring and classification of lakes in Finland

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Monitoring and classification of lakes in Finland

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