『Abstract
　Dissolved silica (DSi) is an important nutrient for primary production. During the last decades, negative trends in DSi concentrations have been observed in coastal areas globally, with implications for the marine ecosystem. This tendency is mainly attributed to two processes: decrease in river loadings (as a result of water regulation and building of dams) and eutrophication in the coastal zone, with subsequent silica depletion. One such area affected by both an intensive water regulation and eutrophication is the Baltic Sea.
　The present study focused on the pelagic DSi trends in different parts of the Baltic Sea for the last three decades. It was found that there are decreasing trends for most of areas and water depths ranging between -0.05 and -1.2μmol Si l^-1 y^-1. The trends are levelling out during the last decade. Since the riverine load of dissolved silica has not changed at a corresponding rate during the time period, the decrement is assumed to be mainly a result of the ongoing eutrophication within the marine water body. This assumption was strengthened by the increasing trends of inorganic nitrogen and phosphorus.

Keywords: silica; trend; nutrient; Baltic Sea; eutrophication; riverine load』

『要旨
　溶存シリカ（DSi）は一次生産にとって重要な栄養分である。この１０年間に、DSi濃度の減少傾向が、海洋生態系に関係して、世界的に海岸地域で観察されている。この傾向はおもに２つの過程に起因する：その後にシリカ枯渇を伴う、河川負荷量の減少（水規制とダム建造の結果としての）および海岸地帯での富栄養化。厳しい水規制と富栄養化の両方の影響を受けたそのような地域の一つがバルト海である。
　本研究は、この３０年間におけるバルト海の異なる場所での外洋DSiの動向に焦点を合わせた。ほとんどの地域と水深で-0.05 〜 -1.2μmol Si/リットル/年の範囲で減少する傾向がみられた。この傾向はこの１０年間に安定している。溶存シリカの河川負荷量はこの期間には類似の速度で変化していないので、その減少量はおもに海水で進行した富栄養化の結果と思われる。この想定は無機の窒素とリンの増加傾向により強化された。』

1. Introduction
2. Study area - the Baltic Sea
　2.1. Geographical characteristics and hydrography
　2.2. Eutrophication and nutrient load
3. Statistical methods and data material
　3.1. Data material
　3.2. Statistical methods
4. Results
　4.1. Descriptive statistics
　4.2. Trend analyses
　　4.2.1. Dissolved silica
　　4.2.2. Dissolved inorganic nitrogen
　　4.2.3. Dissolved inorganic phosphorus
5. discussion
　5.1. DSi trends - present and previous results
　5.2. Precipitation and run-off
　5.3. River loads
　5.4. Eutrophication effects interpreted from nutrient trends
　5.5. Influence of the vertical distribution of salinity
6. Conclusion and future implications
Acknowledgement
References

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