Is it possible to improve the state of the Baltic Sea by artificial oxygenation?

Transcription

1 Educators for the Baltic Sea Seminar , SYKE Is it possible to improve the state of the Baltic Sea by artificial oxygenation? Heikki Pitkänen Marine Reseach Centre SYKE

2

3

4 The problem of hypoxia/anoxia and internal loading in the Baltic Sea There is not enough oxygen in the deeper water layers for aerobic bacterial decomposition of sedimenting organic mater originating from (algal) primary production The phenomena is partly natural but the affected areas have increased due to anthropogenic eutrophication (nutrient enrichment) Spatial scale: from small coastal lagoons to large open sea basins Temporal scale: from seasonal (few months) up to tens of years Various restoration methodologies have been suggested to counteract (dredging, chemical precipitation, oxygenation, biomanipulation)

5 Main processes affecting oxygen in shallow and deep waters of the Baltic Sea HELCOM 2009

6 Vicious circle: nutrient removal and retention capacity drastically decreases Vahtera et al. 2007

7 Internal load of eutrophying nutrients depends on the state of bottom sediment Lehtoranta J. Poor oxygen conditions: -Black sediment up to the surface -No higher life -High nutrient release (=internal load) to water Good oxygen conditions: -Braun sediment surface -Rich benthic fauna -Retains nutrients

8 The role of benthic fauna: the ventilation sediment surface promotes the retention of nutrients Depth in s Storgadden Storfjärden January 2000 water sediment O 2 (mg l -1 ) Lehtoranta, unpubl. Pischedda et al. 2008,Acta Biotheor. 56:

9 Areas of long-term and seasonal hypoxia in in the open Baltic Sea HELCOM 2009

10 Oxygen deficiency is also a coastal water problem Oxygen conditions at the sediment surface in 30 coastal stations in the Gulf of Finland monitored in Seppo Knuuttila/SYKE

11 Deep water oxygen trends in the northern Baltic Sea (HELCOM 2009) HELCOM 2009 HELCOM 2009

12 PROPPEN-Project (Controlling benthic release of phosphorus in different Baltic Sea scales) Main funder: the Swedish EPA (Naturvårdsverket) Coordinator: SYKE/ Marine Research Centre Participants: 9 research institutes and companies from Denmark, Finland, Norway and Sweden By using coastal experiments and laboratory tests to study is it possible to counteract oxygen deficit and internal loading by artificial oxygenation Based on the results, it will be assessed: The availability of the used method in larger coastal and open sea areas Cost-efficiency and cost-benefit Ecological, technical and socio-economic risks Efficiency with (and without) reductions in external nutrient loads

13 PROPPEN Partners SYKE, Marine Research Centre (Coordinator) Helsinki University, Dept. of Economics and Management Helsinki University, Tvärminne Zoological Station Pöyry AS, Norway Pöyry Environment, Finland National Environment Reserach Institute (NERI)/ Aarhus University, Denmark VitusLab, Denmark Water-Eco, Finland Stockholm Vatten, Sweden

14 Experimental areas Sandöfjärden: 6 pumps Lännerstasundet: 1 pump Manual monitoring (physical-chemical- -biological) The pumps will be set on gradually 2009: background conditions and small experiments Sandöfjärden, near-bottom oxygen (mg/l) oxygen, mg/l year Päivi Korpinen, Heikki Pitkänen/ SYKE, Map copyrights: Merenkulkuhallitus, Maanmittauslaitos,Sjöfarstverket

15 Working principle of the Mixox-pump Beginning Hypolimnion After 1 month Hypolimnion Mixox-pump Erkki Saarijärvi/ Vesi-Eko,

16 Intensive automatic measurements are needed to follow short-term effects of oxygenation Dist to MIXOX 100m Sandöfjärden MIXOX (measuring scheme) RCM9 (O 2, C, T) Depth 3m Surface float Boyancy floats (6-9) Min dist X X=tan(20)*depth T Float with weather station and possible GPRS Min dist about 30m Power line for RDCP RCM9 (O 2, C, T) Depth 10m T Floating rope Floating rope Temperature loggers T RCM9 (O 2, C, T) Depth 20m 20 degrees T Oxygen optode 0.5m sinking rope (or according to wished instrument depth) Anchoring weight (60kg lead) RDCP Anchoring weight Paula Väänänen/SYKE

17 Model simulations Modeled effect of oxygenation on a coastal water area The pumping increases mixing and decreases the age of water especially in deep layers Jørgen Bendtsen/Vituslab & Kai Rasmus/SYKE

18 What kind of results can be expected in coastal areas? Deep water oxygen will increase at least close to the pumps (+) Toxic hydrogen sulphide will decrease or disappear (+) The increase of deep water temperature accelerates oxygen consumption there, and takes a part of the advantage (-) There is a risk of the upwelling of deep water nutrients and even hydrogen sulphide into the upper water layers, if the pumping is too effective (-) Based on existing information, effects on sediment and bottom fauna will probably remain small. In areas suffering from seasonal hypoxia possibilities are in any case much better than in areas suffering from long-term hypoxia (+/-)

19 General conclusions Artificial oxygenation is not an alternative for traditional measures aimed at reducing nutrient loads, but it may help the recovery at least in coastal scales Large-scale applications in the open sea scale are not relevant at the moment: even if technical problems could be solved, there is a great risk to cause adverse effects and/or change the ecosystem to an unpredictable/unintended direction (EIA is needed!) The basic and most important measure is to further strongly decrease the present nutrient loading (HELCOM/BSAP) Careful small scale experiments are needed to find out the ecological, technological and socio-economic availability of the methodology

20 Thank you!