Anne Tarvainen Ilkka Sammalkorpi Liisa Laitinen Finnish Environment Institute

1. Submerged aquatic vegetation – a nuisance in Finnish lakes ? Lakepromo Biodiversity Seminar in Brighton 26.-28.20.2005 Anne TarvainenIlkka Sammalkorpi Liisa Laitinen Finnish Environment Institute

2. Contents • Aquatic weed and vegetation situation in Finland • Results from a national inquiry by SYKE in summer 2005 • Case studies • Lake Ruutinlampi • Lake Matalajärvi • Conclusions and research & development needs

3. Aquatic vegetation overgrowth situation in Finland • Overgrowth of aquatic vegetation is a problem in appr. 1 000 sites (lakes, ponds or bays) • Nuisance species are mainly emergent species (Phragmites australis, Equisetum fluviatile) and floating leafed (Nuphar spp, Nymphea spp.) vegetation • Inquiry in summer 2005 about submerged species • Answers from 73 areas (10 bays and 63 lakes, divisions of the lake or ponds) • Inquiry didn’t reach all. Estimate is that appr. 100-300 sites are suffering overgrowth of submerged vegetation

4. A media favourite • In Finland recreational use of watercourses is extensive especially during the summer. There are 450 000 summer cottages and most of them are situated next of near to watercourses. • Recreational users of water courses are demanding better circumstances without knowledge of aquatic environment. • all aquatic vegetation is considered harmful • demand of easy and quick solutions • Problem has been discussed in several newspapers, magazines and TV programs • Grass root level instructions are needed

5. Geographical distribution of problematic cases

6. The reported nuisance taxa • From Potamogeton species most common for nuisance were Potamogeton perfoliatus and Potamogeton natas, which are very common in Finland • Aquatic bryophytes were most common in northern and eastern areas of Finland, but also in some areas in the south. • Other species were emergent and floating leafed species

7. Canadian waterweed (Elodea canadensis) Rigid hornwort (Ceratophyllum demersum) Species involved Spiked water-milfoil (Myriophyllum spicatum)

8. Timing of the problem • On several sites reported in inquiry submerged vegetation has caused problems since 1960’s. • Canadian waterweedwas brought to Finland 1884 to Botanic Garden in Helsinki. It has been causing problems since it arrival. • In several lakes SAV (submerged aquatic vegetation) has caused problems only since 2000. • Interesting was that nuisance caused by Myriophyllum species were reported mainly in 2001-2004.

9. The difficulties caused by excessive SAV Other nuisances • Smell • Blockage of currents and water exchange

10. Used restoration methods • Mowing has been the most commonly used method to control aquatic vegetation • mainly suitable for emergent species • Harvesters are quite commonly used • leaves plant fragments • Seines have successfully used in some small areas • potential to develop new practices • Freezing was tested in 1980’s • Experiments with Myriophyllum species during the winter 2005-2006 in two sites • Also dredging and raising of the water level have been used e.g. in bird lakes • Best results have been achieved repeating restoration methods and combining several restoration methods

11. Funding the restoration actions • Most common financiers • towns or municipalities • private persons • regional environmental centres • local fishing associations • some cases also EU funding • Possibilities of sponsor by companies • Voluntary work is essential! Also local participation and community spirit are key factors in successful restoration projects!

12. Conservational values of the sites • 11 of the sites reported in inquiry there were protectorates or threatened plant or bird species were present • 10 Natura sites! • endangered or near threatened aquatic plants: Potamogeton pusillus , Potamogeton rutilus, Najas tenuissima, Callitriche hermaphroditica and Ranunculus confervoides • 12 of sites were important bird sites

13. Cases • Totally 5 cases • Follow up of vegetation and restoration in summer 2005 • Estimation of restoration action efficiency • Some experimental test • Lake Kalaton, pH-regulation • Follow up of removed vegetation species composition

14. Ruutinlampi, Nummi-Pusula • Area 9 ha, maximum depth 1,7 m • Restoration has been launched and carried on by private farmer Aarre Arrajoki • Most common species Elodea canadensis, Nuphar lutea, Potamogeton natans also Ceratophyllum demersum • Internal and external loading • Extensive vegetation causes oxygen depletion during the winter and raises pH even to over 9 in summer • Elodea has been removed with seines and rakes attached to the boat • During the winter lakes has been oxygenated with sludge pump • During the summer 2005 SAV-vegetation was exceptional sparse.

16. Lake Matalajärvi, Espoo • Surface area 112 ha • A NATURA 2000 target area (Najas tenuissima) and an IBA area for waterfowl protection • Project operated by L. Matalajärvi Association, a volunteer NGO of local stakeholders. • Ceratophyllum d. hampers recreational use and threatens existence of endangered Najas tenuissima. • Funded by the City of Espoo, Kehu association, Uusimaa regional environment centre and sponsored (15 %) by local companies. • Monitoring data of the flora in 1961, 1997 and 2000 (also aerial photographs) • Large layers of fragments of Ceratophyllum were found in areas treated by the harvester • Restoration and follow up continues…

17. Najas tenuissima • N. tenuissima is one of the most threatened species in Europe and almost all known populations are in southern Finland. • Present populations are known from 18 lakes and one marine estuary. • Nearly 40 % of the present populations are included in the Natura 2000 network.

19. Research & development needs • Reasons for the he explosion in 2002-2004. Combined effects of water level fluctuations, washout, transparency and temperature? • The ecological role of SAV in relation to restoration / management measures and their impact (increased transparency) • Comparison of available removal or control methods • development of seines and freezing • Efficiency of methods for removal of SAV – particularly selective removal of Ceratophyllum and Elodea by seining to increase biodiversity • Lakes with Najas tenuissima or other endangered SAV species • Identification of naturally productive lakes and considerations of their management need • Information & education to the grass root level and stakeholders • Identification guides to the public