The Swedish monitoring of surface waters: 50 years of adaptive monitoring

Abstract

For more than 50 years, scientific insights from surface water monitoring have supported Swedish evidence-based environmental management. Efforts to understand and control eutrophication in the 1960s led to construction of wastewater treatment plants with phosphorus retention, while acid rain research in the 1970s contributed to international legislation curbing emissions. By the 1990s, long-time series were being used to infer climate effects on surface water chemistry and biology. Monitoring data play a key role in implementing the EU Water Framework Directive and other legislation and have been used to show beneficial effects of agricultural management on Baltic Sea eutrophication. The Swedish experience demonstrates that well-designed and financially supported surface water monitoring can be used to understand and manage a range of stressors and societal concerns. Using scientifically sound adaptive monitoring principles to balance continuity and change has ensured long-time series and the capability to address new questions over time.

Fig. 1

Development of the Swedish national surface water monitoring program in response to environmental pressures. During the 1960s, monitoring developed from a research project to a government-financed program runs at Uppsala University. During the 1970s, the focus was broadened from eutrophication toward acidification. Further, surface waters were incorporated into a national monitoring program for all ecosystems (PMK), and the monitoring group and laboratories were organizationally moved to the Swedish Environmental Protection Agency (SEPA), although co-located with the Limnology department at Uppsala University. During the 1980s, the focus on acidification was reinforced by monitoring of small reference lakes and streams, as well as expanding the parameter list with trace metals and littoral fauna. In 1989, a monitoring program focused on limed lakes and streams started (ISELAW). Further lake surveys based on a random selection were performed since 1990. Fish monitoring, performed by the Fisheries Board, was integrated into the ISELAW program in 1994 and other national surface water monitoring programs in 1997. Problems with persistent organic pollutants (POP) had been on the agenda since the early 1960’s, but it was not until 1997 that POPs were included in the surface water monitoring program. The acidification focus was further strengthened by the start of the new program of integrated monitoring of small catchments. In the year 2000, the EU Water Framework Directive (WFD) was ratified. This led to the development of biological monitoring and the inclusion of more sites and the addition of benthic epiphytes and macrophytes to the parameter list. As acid deposition declined markedly, focus of the monitoring in the small lakes and streams as well as the integrated monitoring shifted toward climate change, where the long-time series have shown to be extremely valuable. In 2011, the responsibility of the surface water monitoring was changed from SEPA to a new authority SwAM (The Swedish Agency for Marine and Water Management)

Fig. 2

Recovery from eutrophication in Ekoln after introduction of improved wastewater phosphorus removal in 1973. a Total phosphorus (TP) concentrations at Flottsund in the Fyrisån immediately downstream of the wastewater treatment plant and TP and chlorophyll at Ekoln, in Mälaren near the Fyrisån outlet. b Annual average Fyrisån flows and Ekoln TP. c Ekoln summer hypolimnetic oxygen concentrations versus average annual TP. Ekoln bottom waters still experience periods of oxygen stress (c), and an inverse relationship exists between TP and hypolimnetic oxygen minima. As long as average TP exceeded about 40 µg L⁻¹, minimum hypolimnetic oxygen concentrations remained below 2 mg L⁻¹. In recent years, there has been no clear relationship between average TP and minimum oxygen concentrations. Lower TP concentrations at Ekoln sometimes but not always result in hypolimnetic oxygen concentrations more likely to support viable biological communities

Fig. 3

Recovery of the acidified lake Övre Skärsjön showing trends in sulfate deposition, in-lake sulfate concentration, pH, and the Henriksen–Medin benthic community acidification index. Since the mid 1980s, declines in S deposition have been reflected in declining in-lake sulfate concentration and increasing pH. The decline in-lake sulfate concentration is less than that in deposition due to soil retention processes. Between 1987 and 2010, pH has increased by ~1 unit, which is slightly larger than within year variation. This pH increase is associated with biological community improvements where Henriksen–Medin index values have increased since the mid 1980s. These results show the value of complementary biological and chemical data for assessing the efficacy of emissions control scenarios. Increasing pH and improvements in biology can be unequivocally linked to declining acid deposition, but significant within year variation in pH which shows the need for frequent monitoring to correctly identify both trends and variability

Fig. 4

Monitored river mouths within the Swedish national monitoring program 2014 with catchment borders given. The 47 monitored rivers cover runoff from 82 % of the surface of Sweden. Bright color denotes non-monitored areas, and dark color denotes catchment areas outside Sweden (i.e., Norway and Finland)

Fig. 5

Trend lakes within the Swedish national monitoring program 2013. The form of the symbol denotes sampling program. Black symbol denotes banking of fish tissue. The trend lakes include 108 lakes with ten lakes more intensively monitored. The lakes are reference lakes in terms of point sources and intensive local land use, but may be affected by large-scale airborne pollution and extensive land use

Fig. 6

Monitored streams within the Swedish national monitoring program 2014. The form of the symbol denotes the catchment size, and color denotes the sampled parameters. The national program for trend streams includes 67 streams with catchment size between 1 and 10 000 km². The 29 sites with all parameters are regarded as reference stations for defining reference conditions for ecological status. The other stations might be affected by diffuse pollution, acidification, or eutrophication

Fig. 7

Monitored stations in the three large lakes Vänern, Vättern, and Mälaren within the national Swedish monitoring program