『Abstract
　Historical phosphorus (P) dynamics were studied using sediment cores from three oligotrophic, acidic lakes in Maine, USA. Long-term oligotrophy of these lakes is consistent with high sediment aluminum (as Al(OH)3) concentrations, as Al inhibits internal P loading, even under reducing conditions. The role of microbially-mediated reactions in controlling redox conditions was evaluated by estimating microbial biomass and relative abundance of specific functional groups. Sediments were fractionated using a sequential chemical extraction technique and all lakes met criteria for P retention based on threshold sediment concentrations of Al, Fe, and P fractions as determined by (Kopacek（aの頭に´、cの頭にv） et al. (2005) Limnol Oceanogr 52: 1147-1155). Sediment NaOH-extractable molybdate-reactive P (rP) and non-reactive P (nrP) represent P associated with non-reducible phases, and organic matter-related P, respectively. Total P (TP) does not decrease with sediment depth, as is typical of eutrophic lake sediments; however, nrP/rP decreases and rP/TP increases for all three lakes, indicating nrP mineralization without any significant upward diffusion and release into the hypolimnion; i.e. diagenesis of P is conservative within the sediment. Two diagenetic models were developed based on nrP and rP concentrations as a function of sediment age. The first model assumes a first-order decay of nrP, the rate coefficient being a function of time, and represents irreversible nrP mineralization, where the produced PO4 is permanently sequestered by the sediment. The second model assumes a first-order reversible biotic mineralization of organic O followed by incorporation of inorganic P into microbial biomass. Both models reflect preservation of TP with no loss to overlying water. The rate coefficients give us insight into qualities of the sediment that have affected mineralization and sequestration of phosphorus throughout the ²¹⁰Pb-dateable history of each lake. Similar models could be constructed for other lakes to help reconstruct their trophic histories. Paleolimnological reconstruction of the sediment P record in oligotrophic lakes shows mineralization of nrP to rP, but unlike the case in eutrophic lake sediments, sediment TP is preserved in these sediments.

Keywords: Lake sediment; Mineralization; Oligotrophic lake; Phosphorus; Sediment microbes; Sequential extraction』

Introduction
　Site descriptions
Materials and methods
　Sediment collection and processing
　Sediment chemistry
　DNA extraction and quantitative PCR
Results
　Sediment chemistry
　Model A: Variable rate coefficient in the transformation of nrP (the irreversible model)
　Model B: Reversible reaction between nrP and rP (the reversible model)
　Microbial analysis
Discussion
　Role of aluminum in lake trophic state
　Transformation models
Conclusions
Acknowledgments
References

連続抽出		抽出物など
湿った堆積物 1 g以上
1	1M NH4Cl、pH 7、 25℃、1時間	ゆるく吸着した、 交換可能な、 孔隙水画分
2	0.1M NaHCO3でバッファーした、 0.1M Na2S2O4（bicarbonate-dithionite、BD）、 40℃、30分	還元剤で可溶な画分〔主に、鉄とマンガンの（オキシ）水酸化物に伴うP〕
3	0.1M NaOH、 25℃、16時間	いくらかのアルミニウムと鉄（オキシ）水酸化物に伴うP、 いくらかの有機と生物起源P
4	0.5M HCｌ、 25℃、16時間	酸溶解鉱物
5	1M NaOH、 85℃、24時間	残り
AlとFeとPに対するPsenner et al. (1988)による連続抽出法の一部を変えたもの。最初のステップで、蒸留水の代わりにNH4Clを使用（Tessier et al. 1979）、第三ステップで1M NaOHの代わりに0.1M NaOHを使用（Hieltjes and Lijklema 1980）。