Humborg,C., Pastuszak,M., Aigars,J., Siegmund,H., Morth（oの頭に¨）,C.-M. and Ittekkot,V.(2006): Decreased silica land-sea fluxes through damming in the Baltic Sea catchment - significance of particle trapping and hydrological alterations. Biogeochemistry, 77, 265-281.

『バルト海流域でのダムを通じたシリカの陸-海フラックスの減少−微粒子トラップと水文変化の重要性』

『Abstract
　We tested the hypothesis that reservoirs with low water residence time and autochthonous production influence river biogeochemistry in eutrophied river systems draining cultivated watersheds. The effect of a single artificial water reservoir and consecutive reservoirs on silica (Si) river fluxes is exemplified by the moderately dammed Vistula River and the heavily regulated Daugava River that are compared with the practically undammed Oder River. The sum of the discharge weighted annual mean biogenic silica (BSi) and dissolved silicate (DSi) concentrations in the rivers Oder, Vistula and Daugava were about 160μM (40 + 120μM), 150μM (20 + 130μM) and 88μM (6 + 82μM), respectively. Assuming BSi and DSi concentrations as observed in the Oder River as typical for eutrophied but undammed rivers, complete trapping of this BSi could have lowered Si fluxes to the Baltic Sea from rivers with cultivated watersheds by 25％. The superimposed effect of hydrological alterations on reduced Si land-sea fluxes is demonstrated by studies in the boreal/subarctic and oligotrophic rivers Kalixalven（後のaの頭に¨） and Luealven（aの頭に¨）. The DSi yield of the heavily dammed Luealven（aの頭に¨）(793 kg km-2 yr-1) constituted only 63％ of that was found in the unregulated Kalixalven（後のaの頭に¨）(1261 kg km-2 yr-1), despite the specific runoff of the Luealven（aの頭に¨）(672 mm m-2 yr-1) being 19％ higher than that of the Kalixalven（後のaの頭に¨）(563 mm m-2 yr-1); runoff normalized DSi yield of the former, regulated watershed, was only half the DSi yield of the latter, unperturbed watershed. Based on these findings, it is hypothesized here that perturbed surface water-groundwater interactions are the major reasons for the reduced annual fluctuations in DSi concentrations as also seen in the heavily dammed and eutrophic river systems such as the Daugava and Danube.

Key words: Silica; Dissolved silicate; Biogenic silica; Retention』

Introduction
Methods
　Investigation area
　Dissolved silicate and biogenic silica measurements
Results
　Cultivated agricultural watersheds
　Boreal/subarctic watersheds
Discussion
　Trapping effect of reservoirs with low water residence times
　Hydrological alterations
Conclusions
Acknowledgements
References

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