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The State of Finnish Coastal Waters in the 1990sAuthor(s): Pirkko Kauppila and Saara BäckSource: AMBIO: A Journal of the Human Environment, 31(3):260-261. 2002.Published By: Royal Swedish Academy of SciencesDOI: http://dx.doi.org/10.1579/0044-7447-31.3.260URL: http://www.bioone.org/doi/full/10.1579/0044-7447-31.3.260

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260 © Royal Swedish Academy of Sciences 2002 Ambio Vol. 31 No. 3, May 2002http://www.ambio.kva.se

This paper is based on the coastal monitoringdata produced by the Finnish EnvironmentalAdministration and was compiled by theFinnish Environment Institute. The chemicalmonitoring data in open-sea areas originatedfrom the Finnish Institute of Marine Re-search.

NUTRIENT LOADING DECREASEDDuring the 1990s, Finnish coastal waters re-ceived, on average, 4100 tonnes (t) totalphosphorus (TP) and 74 000 t total nitrogen(TN) per year from Finnish territory, cor-responding to c. 10% of the total load ofnutrients to the Baltic Sea. In the Finnishcatchment, agriculture was the main anthro-pogenic source of TP and TN loading (Fig.1). The municipal load of TN was the secondlargest and atmospheric deposition the thirdlargest source of TN load. Regarding TPload, forestry was the second and scattereddwellings the third largest source. The majorpart of the load from forestry was carried viathe large northern rivers to the Bothnian Bay(Fig 1).

The load of TP has decreased by c. 16%and the load of TN c. 10% from levels in the1980s. In particular, reductions in municipaland industrial loads of TP have beensignificant. By contrast, changes in diffuseloading were only slight. The decline in thetotal load of TN since the late 1980s wasexplained by the decrease in the water flow inthe 1990s, because the point source loadingof TN actually slightly increased during thatperiod.

SOME DECREASING TRENDS INNUTRIENT CONCENTRATIONSSome clear changes in nutrient distributionsin Finnish coastal waters can be foundbetween the present period of study, (1991–1998), and 1979–1983 (1). In the open sea,the most extensive is the increase in thewinter level of TP in the Bothnian Sea,whereas in the eastern Gulf of Finland adecrease of c. 20% has taken place in theaverage level of TP, probably reflecting thedecreased load from the River Neva—St.Petersburg region in Russia. In the coastalwaters, the most striking changes betweenthe early 1980s and the 1990s were theincreases in winter TN concentrationsexceeding 500 mg m–3 in the middle andinner Archipelago Sea and in parts of thecoastal Bothnian Bay. Regarding changes inP distribution, the area of TP concentrationsexceeding 40 mg m–3 has decreased in watersoff the large point source loaders in theBothnian Sea, most probably due to decrea-ses in the municipal and industrial (pulp andpaper industry) loadings of P to these coastalwater areas.

The decreasing trends of N in both theopen sea and in coastal waters in the 1990swere most probably connected to the decreasein N loading by over 30% to the Gulf ofFinland during the decade. However, theincrease of P, despite the decreased external

The State of Finnish Coastal Watersin the 1990s

Synopsis

loading, was due to the strong increase ininternal P loading in the mid-1990s (Fig. 2).Thus, the nutrient limitation clearly shiftedmore pronouncedly towards N control dur-ing the 1990s. The most striking sign of this

was the increase of unfixed DIP in the outercoastal waters up to 10 to 20 mg P m–3 in JulyAugust 1997–1998, causing strong bloomsof Nodularia spumigena in the warm sum-mer of 1997 (Fig 2).

Figure. 1. Source apportionment of the annual average (1991–1996) of the Finnish total loads ofP and N (t yr–1) entering into different sea areas. Note that nutrient loads from Sweden, Estoniaand Russia are not included.

Figure. 2. Wintersurface values(1–5 m) of Total N,inorganic N (DIN),Total P andinorganic P (DIP)at Huovari in theeastern Gulf ofFinland, at Länsi-Tonttu off HelsinkiCity, at Seili in themiddle ofArchipelago Sea,at Bergö in thenorthern BothnianSea and at Hailuotoin the northeasternBothnian Bay inwinter 1979–1998.

261Ambio Vol. 31 No. 3, May 2002 © Royal Swedish Academy of Sciences 2002http://www.ambio.kva.se

In the 1990s, eutrophication continued inthe Archipelago Sea (2, 3). However, in-creasing nutrient trends can be discernedonly for phosphate and TP, while DIN de-creased (Fig. 2). In the 1970s and the 1980s,increasing trends in both P and N concentra-tions were evident, which could be explainedby intensified agriculture and fish-farming(4). However, in waters off large towns Pconcentrations showed decreasing trends, dueto the introduction of P precipitation at themunicipal treatment plants.

In the middle of the Archipelago Sea, adrastic increase in DIP, from 10 to 30 mg Pm–3 in summertime near-bottom concen-trations, took place during the late 1980s andthe 1990s. At the same time, the deep-wateroxygen concentrations continuously decrea-sed and reached 6–7 mg L–1 c. 50% satura-tion, in 1997. These phenomena indicateincreased sedimentation of organic detrituscaused by increased primary productionand/or possible anoxia and internal loadingat the sediment-water interface. In general,less clear changes are found in the rest of theGulf of Bothnia. A decreasing trend in winterDIN appears possible during the 1990s in thecoastal waters (Fig. 2). The open Gulf valuesalso support similar conclusions. There mayalso have been changes in the limitationbalance between N and P, due to the in-creased P concentrations in the open BothnianSea, possibly caused by the decreased verticalstability.

In the NE Bothnian Bay, the clear decrea-ses in both N and P concentrations since thelate 1980s (Fig. 2) can most probably beattributed to improvements in sewage-treatment techniques and to less river runoffin the 1990s. The trend was more pronouncedfor P than for N. The decrease of total-P by 4to 5 mg m–3 during this period is in accordancewith the reduction of the load of P from localpoint sources by about 50%.

EUTROPHICATIONEXPRESSED AS CHLOROPHYLL aCONCENTRATION ANDPHYTOPLANKTONMost of the Finnish coastal waters areeutrophied compared to open sea areas. Theeutrophied zone (more than 5 mg chl a m–3)along the coast of the Gulf of Finland and theArchipelago Sea can be explained by theeven distribution of riverine nutrient loaddirected to the coastal areas. In the Gulf ofBothnia, eutrophied coastal areas were limitedto estuaries or archipelagos off the largecities. For the open sea, only the eastern Gulfof Finland is clearly eutrophied due to aconsiderable load of nutrients and also to thecurrent and mixing conditions.

Changes in trophic status since the 1970sexhibit 2 opposite directions. Some clearlyeutrophied waters off large cities, e.g. theHelsinki Espoo region and Oulu, show im-provements that are largely due to the de-crease in municipal and industrial nutrientloading. However, the total surface area ofthe coastal waters defined as eutrophied(more than 5 mg chl a m–3) has increasedduring the 1980s. The situation in the 1990shas not essentially changed compared to thatof the 1980s. During the 1980s, the border ofslightly eutrophied areas moved westwards

in the Gulf of Finland, in the outer ArchipelagoSea, and in the Bothnian Bay.

The development of eutrophication in theGulf of Finland and the Archipelago Sea wasmanifested as an increase in late summerphytoplankton biomass, and as changes inspecies composition. In the eastern Gulf ofFinland, the increasing trend of phytoplanktongenerally followed the trend of nutrients.However, the increase in phytoplanktonamounts levelled off in the late-1990s inkeeping with P concentrations, which due toextensive oxygen deficit were elevated in themiddle of the decade. The dominance of bluegreen algae has increased since the late 1980s.The nutrient ratios and hydrographicalconditions determine which of the blue greenalgae, Planktothrix agardhii or N2-fixingAphanizomenon sp., gain dominance. P.agardhii mainly dominated in summer whennutrient-rich waters extended as far as theeasternmost Finnish archipelago (5, 6).

In the outer archipelago off Helsinki, theincrease in nutrient concentration that occuredwhen purified wastewaters began to beconducted to the open sea was not reflected intotal phytoplankton biomasses. However, theincrease in the inorganic N:P ratio favoredflourishing of the blue green algal orderChroococcales at the expense of Aphanizo-menon sp., which in these altered conditionscould not take advantage of its N2-fixingcapability. Similarly, the decline in phos-phorus concentrations in inner bays resultedin the dominance of non-N2-fixing blue-greenalgae.

In the Archipelago Sea, the increase intotal phytoplankton biomasses in the 1990sas a response to the increase in theconcentrations of P can partly be explainedby internal loading and nutrient fluxes fromthe Gulf of Finland (3). In recent years, thedecrease in the N:P ratio and the increase inN limitation has probably contributed to thedominance of blue-green algae.

Eutrophication in the Gulf of Finland andthe Archipelago Sea has been reflected inincrease in the extent and intensity of algalaccumulations in late summer. Theseaccumulations are rare in the Bothnian Baymainly due to P-limitation and cool watertemperatures. In the algal accumulations,Aphanizomenon sp. and the occasionally toxicNodularia spumigena, are the most commonblue-green algal species, both of which arecapable of fixing atmospheric nitrogen. In1997, the accumulations were most exten-sive and prolonged ever recorded. This phe-nomenon was attributed, in addition to calmand warm weather conditions, to elevatedconcentrations of surface P due to internalloading. In the summers of 1998–2000,accumulations were recorded not only inoffshore waters but, exceptionally, also inthe inner Archipelago Sea, mainly due to anincrease in N limitation. Near the coast and inthe easternmost Gulf of Finland accumula-tions of blue-green algae have consisted ofMicrocystis and Planktothrix, which requireinorganic N in addition to P.

PHYTOBENTHOSDrifting macroalgae have been encounteredin the 1990s in the Archipelago Sea and theÅland Sea and also in small amounts in the

References and Notes1. Pitkänen, H., Kangas, P., Miettinen, V. and Ekholm,

P.1987. The state of the Finnish coastal waters in 1979–83. National Board of Waters and the Environment,Finland. Publications of the Water and EnvironmentAdministration, no. 8, 167 pp.

2. Bonsdorff, E., Blomqvist, E.M., Mattila, J. and Norkko,A. 1997. Long-term changes and coastal eutrophication.Examples from the Åland Islands and the ArchipelagoSea, Northern Baltic Sea. Oceanologica Acta 20, 319–329.

3. Kirkkala, T., Helminen, H. and Erkkilä, A. 1998. Varia-bility of nutrient limitation in the Archipelago Se, SWFinland. Hydrobiologia 363, 117–126.

4. Pitkänen, H. 1994. Eutrophication of the Finnish coastalwaters: origin, fate and effects of riverine nutrient fluxes.National Board of Waters and the Environment, Finland.Publications of the Water and Environment ResearchInstitute, no. 18, 44 pp.

5. Pitkänen, H., Tamminen, T., Kangas, P., Huttula, T.,Kivi, K., Kuosa, H., Sarkkula, J., Eloheimo, K., Kauppila,P. and Skakalsky, B. 1993. Late summer trophic conditionsin the northeast Gulf of Finland and the River NevaEstuary, Baltic Sea. Estuar. Coastal Shelf Sci. 37, 453–474.

6. Kauppila, P., Hällfors, G., Kangas, P., Kokkonen, P. andBasova, S. 1995. Late summer phytoplankton speciescomposition and biomasses in the eastern Gulf of Fin-land. Ophelia 42, 179–191.

7. Vahteri, P., Mäkinen, A., Salovius, S. and Vuorinen, I.2000. Are drifting algae mats conquering the bottom ofthe Archipelago Sea, SW Finland. Ambio 29, 338–343.

8. Lehvo, A. and Bäck, S. 2001. Survey of macroalgal matson southeastern Baltic coast of Finland. Aquatic Conserv.Mar. Freshw. Ecosyst. 11, 11–18.

9. This synopsis is the short version of the summary of therecently published assessment report: Kauppila, P. andBäck, S. (eds) 2001. The state of Finnish coastal watersin the 1990s. The Finish Environment 472, 132 pp.

Pirkko Kauppila, Research ScientistFinnish Environment InstituteResearch DepartmentP.O. Box 140, FIN 00251 HelsinkiFinlandE-mail: pirkko.kauppila@vyh.fi

Saara Bäck, Research ScientistFinnish Environment InstituteResearch DepartmentP.O. Box 140, FIN 00251 HelsinkiFinlandE-mail: saara.back@vyh.fi

eastern Gulf of Finland (7, 8). When thefilamentous macroalgae are detached fromthe rocky shores they are transported to thesublittoral, where they may form loose-lyingdrift mats. As a result, the natural littoralvegetation can be replaced and the bottomfauna can be altered by an algal mat coveringthe available substrata.

In the 1990s, the distribution area of blad-der wrack, Fucus vesiculosus, still reachednorthward up to the Quark and in the easternpart of the Gulf of Finland extended toVirolahti. After an extensive decline of F.vesiculosus stands in SW coasts of Finlandin late 1970s, the first signs of recovery wereobserved in the early 1980s. In the Archi-pelago Sea, F. vesiculosus had also com-pletely vanished from many localities in theearly 1980s. By the late 1980s and the early1990s this species had partly recolonized itsformer habitats, but the decline had continuedin some parts of the archipelago. In earlierstudies, F. vesiculosus was recorded asgrowing at a depth of 10 m in the Tvär-minne archipelago of the western Gulf ofFinland but in the 1990s its maximumgrowth depth was about 5 to 6 m with anoptimum of 2–3 m. In the Archipelago Sea,nowadays, the continuous belt of F.vesiculosus reaches only a depth of 1.0 to 4.0m although individual plants may be founddown to a depth of 7–8 m.