Classification of surface waters on the basis of their ecological and chemical state
Ecological state
Evaluations of the ecological state of water bodies primarily focus on biological factors. In each surface water body1) under assessment, the states of communities of planktonic algae, diatoms, aquatic plants, benthic fauna and fish are compared to conditions that would prevail if human activities had no observable impacts on aquatic life. Water bodies’ ecological quality is highest where human impacts are lowest. Evaluations also consider other water quality factors (total nutrient content, pH, transparency) and hydromorphological factors (including average winter water level decline, and obstacles hindering the movements of migratory fish).
| Quality factor |
Rivers
|
Lakes
|
Coastal waters
|
| Phytoplankton |
|
x
|
x
|
| Diatoms |
x
|
|
|
| Aquatic plants |
|
x
|
x
|
| Benthic fauna |
x
|
x
|
x
|
| Fish |
x
|
x
|
|
| Physical-chemical factors (water quality) |
x
|
x
|
x
|
| Hydromorphological factors |
x
|
x
|
x
|
Surface waters are classified into five colour-coded categories on the basis of their ecological state.
| Class |
Colour
|
| High |
|
| Good |
|
| Moderate |
|
| Poor |
|
| Bad |
|
Artificial or heavily modified surface waters2) are also classified on the basis of the data available on their ecological state as high, good, moderate, poor or bad. Reference conditions
Different types of surface water bodies with varying natural characteristics cannot be classified according to a single scale. They must first be divaded into type groups of surface waters with similar features. Sets of conditions can then be defined for comparative purposes for each type of surface water body, so as to create specific classification scales. Chemical state
Assessments of the chemical state of water bodies compare the concentrations of harmful and hazardous substances to the environmental quality standards defined in related legislation. Norms have been defined for a total of 53 substances/substance groups. Examples of hazardous substances under assessment include cadmium, lead, organic halogen compounds and organic tin compounds.
Waters are classified according to their chemical state as “good” or “no good”.
1) Surface water bodies include distinct and significant sections of river systems, i.e. lakes; reservoirs; streams, rivers or canals in their entirety or parts thereof; as well as specific areas of Finland’s coastal waters.
2) Artificial surface water bodies include reservoirs and canals constructed on dry land. Heavily modified surface water bodies are natural surface water bodies that have been significantly altered by construction, water level regulation or other activities.
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