**Finnish Environment Institute (SYKE) hoto: Roland Lensch

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1 Increasing organic carbon concentrations in the raw water source of Helsinki H. Poutanen*, A. Räike**, M. Forsius**, V. Vuorilehto* ** Helsinki Region Environmental Services Authority HSY **Finnish Environment Institute (SYKE) hoto: Roland Lensch

2 Organic carbon concentration in Nordic countries Source: Nordic Lake Survey 1995 Humic concentration is high in Finland: Lakes 8.5 mg/l Rivers and streams 14 mg/l Reasons for high OC Flat topography, Low evaporation Cold weather Catchment properties in Finland Forest 46% Peat 16% Lake 10% Field 8%

3 TOC trends in Finland Also in Finland TOC concentrations have increased First signs of the increase were detected in small headwater lakes Upward trend started later than in other Nordic countries Increases have been detected recently also in larger rivers and lakes (Räike et al. 2015) Source: Jussi Vuorenmaa, SYKE

4 Our aims: Estimate sources of OC inputs in the Lake Päijänne catchment and possible changes in the loading Assess trends in OC concentrations between 1975 and 2014 Evaluate the consequences of increasing OC concentrations for water treatment

5 Material We used COD Mn as a proxy for TOC concentration The correlation is generally good between these two parameters Inorganic substances which consume oxygen weaken the relation Water quality data of lakes and rivers originated from the database of the Finnish Environment Institute Water quality data of raw water originated from Helsinki Region Environmental Services Authority

6 Lake Päijänne Finland s second largest lake Drainage area km2 Surface area 1083 km2 Volume 18.1 km3 Average depth 16.2 m Water residence time 2.5 yr CODMn concentration varies between 2.5 mg/l to 15 mg/l Concentrations are lower in southern part due to mineralisation in the lake Water intake for Päijänne Tunnel

7 Päijänne Water Tunnel World s second longest tunnel: 120 km Provides fresh water for the Helsinki metropolitan area Construction started 1972 and was completed in 1982 Enabels a water flow of 10 m 3 s -1 Annual raw water flow in the tunnel 94 Mm 3

8 Trends in COD Mn concentrations COD concentrations decreased from 1975 to 1995 due to decreased point source loading Increase started approx. 10 years ago The upward trend was ubiquitous, both in time and space We were not able to link the changes to any specific catchment characteristics Likely drivers: Warming climate, changes in hydrology and decreases in acidic deposition

9 Trends in TOC concentrations in the Päijänne Tunnel Clear increase in TOC concentration Increase started 2008 has been continuing since then Year 2008 was extremely wet and the water level in the lake was high In addition the winter was warm in 2008

10 HSY s treatment process HSY s treatment process: iron coagulation Sedimentation rapid sand filtration ozonation two step activated carbon filtration UV and Chloroamine disinfection

11 Consequences to the water treatment The TOC load going to ozona7on and AC process has grown Greater ozone doses, resul7ng in greater amounts of easily biodegradable compounds The subsequent biofiltra7on may not be able to remove the increased amount of biodegradable mager Increased microbial growth in distribu7on network Disinfec7on efficiency will also be affected by increasing NOM concentra7ons.

12 Conclusions Drivers seem to be related to climate and acidic deposition Warm winters and increasing winter flow are likely to cause further increases in TOC concentrations in the future OC concentrations have increased in the inflowing river water, in Lake Päijänne, and in the raw water Increase in raw water OC concentration sets challenges to coagulation process, and if not met could lead to problems in network water quality.

13 Acknowledgements We are grateful to NordForsk funded DOMQUA (Drinking water treatment adaptation to increasing levels of DOM and changing DOM quality under climate change) project for supporting this work