Trend lakes

The subprogramme provides an annual overview of the environmental status of Sweden’s lakes and serves as a foundation for official statistics. The lake status assessments are used to follow up on national environmental quality objectives and for international reporting and agreements, such as the UN Convention on Long-range Transboundary Air Pollution (CLRTAP).

We use data from the Trend Lake Stations Subprogramme to support the ongoing development and evaluation of assessment criteria for the environmental status of Swedish lakes.

Sampling

The subprogramme includes both chemical and biological sampling according to a specific schedule. Surface water chemistry is sampled in all lakes every season, i.e. four times per year. Benthic invertebrates and diatoms are sampled annually. Fish surveys are carried out in selected lakes, though not necessarily every year. Macrophyte sampling is conducted in all lakes at six-year intervals. Ten of the lakes, selected along a climate gradient, are monitored more intensively, with monthly water chemistry sampling, for example.

Scope of the Subprogramme

The Trend Lake Stations Subprogramme includes a selection of 106 lakes across Sweden. These trend lakes are chosen because they are unaffected by local emissions or intensive land use, making them suitable as reference sites for assessing general environmental status and diffuse pollution. The subprogramme includes lakes from the most common limnic types in Sweden.

The lakes monitored in the subprogramme are medium-sized, ranging in area from 0.02 to 52.6 km².

The Trend Lake Stations Subprogramme differs from the closely related River Mouths Subprogramme in its focus on smaller inland waters and the lack of requirement for connection to the sea. It also differs from the Trend River Stations Subprogramme, which includes biological sampling of biotopes. All river trend stations host fish populations, primarily brown trout.

History of the Subprogramme

The Trend Lake Stations Subprogramme began in 2007. Prior to that, similar monitoring was conducted through the former Reference Lakes Programme ("referenssjöar"), which started in the mid-1980s. Between 1995 and 2006, the programme was known as the Time Series Lakes Programme ("tidsseriesjöar"). Some of the lakes were added as recently as 2007, while others have over 40 years of continuous data.

Responsibilities Within the Subprogramme

The Department of Aquatic Sciences and Assessment is responsible for conducting the programme and also hosts the generated data—except for fish data. The Trend Lake Stations Subprogramme is part of the Freshwater programme area within Sweden’s national environmental monitoring system and is funded by the Swedish Agency for Marine and Water Management.