Biological status of surface waters
The status of surface waters can be assessed both by conventional physicochemical surveys and by biological investigations. The populations of fish, invertebrates, aquatic plants and diatoms react to water pollution caused by substance infiltration, control structures and changes in water and sediment regimes.
From a biological standpoint, the status of Swiss surface waters is variable. According to the various bioindicators, the results for the water sections surveyed in 2015 were:
- 30-90%: good or very good ecological status and
- 10-70%: fair to poor status
The explanation for the wide percentage spread is that the groups of organisms surveyed react differently to the different types of pollution.
The diatom bioindicator shows good to very good water quality at about 90% of monitoring stations. This is primarily indicative of the nutrient situation in the waters. Thus the indicator shows that nutrient pollution has fallen significantly in Swiss waters since the 1980s due to the construction of wastewater treatment plants (WTP).
The assessments are less positive for the invertebrates, fish and aquatic plants bioindicators. They show that the habitat quality of the water continues to be impaired. The stresses include deficits in water morphology and passability for fish, poor sediment transport, inadequate water supply (residual flow) or excessive discharge variations (hydropeaking) caused by damming and control structures. Other contributory factors are substance contamination by micropollutants and changes in the temperature regime.
The greatest deficits exist on the intensively used Swiss Plateau, where the waters are structurally impaired, passability for fish is compromised in many places and substance pollution is greatest. The small watercourses are under above-average pressure, largely due to agriculture.
Since fish are the most comprehensive indicator of the various water contaminants, the overall state is assessed as poor.
To date, only two national monitoring campaigns have been carried out. Times series will therefore only be available in the future. For that reason, the trend cannot be assessed. However, it is conceivable that the biological state of watercourses will improve as a result of various measures under the three development objectives: enough space for watercourses, sufficient water supplies and adequate water quality. The revised Waters Protection Act creates the required legal basis, specifically in relation to revitalisation, hydropower remediation and expansion of the WTPs to eliminate trace substances.
- Related indicators
- Nutrients in watercourses
The European Water Framework Directive (WFD, Directive 2000/60/EC) establishes a standardised basis for surface water monitoring in the EU. The Member States assess the various quality components using their own national methods according to the requirements in Annex V of the WFD. In order to ensure comparability of the results between the Member States, the WFD provides for intercalibration of the national methods. The assessment is made as specified in the WFD on a five-step scale, so that the results of surveys in neighbouring countries are comparable with results of surveys in Switzerland at the final classification level.
The invertebrates, diatoms and fish parameters are assessed under the Modular Stepwise Procedure according to five quality classes. A standard Swiss national assessment method for macrophytes is under development as part of the Modular Stepwise Procedure. A provisional assessment in four classes by the procedure proposed by the Canton of Zurich is still in use at present.
The total number of monitoring stations assessed differs for each parameter: invertebrates: 88, fish: 52, diatoms: 88 and aquatic plants: 45 stations.