Lake 227 of the Experimental Lakes Area (ELA) in Ontario, Canada, has been fertilized with phosphorus (P) since 1969, which resulted in a rapid transition from oligotrophic to eutrophic conditions. Sediment cores collected from the oxygenated epilimnion, and the mostly anoxic hypolimnion of this unique lake contain a historical record of the changes in sediment P speciation and burial rates across the trophic transition. To elucidate these changes, results of chemical extractions were combined with ²¹⁰Pb sediment dating, and with ³¹P NMR, Mössbauer, and XANES spectroscopies. Prior to 1969, organic P (P_Org) was the major sedimentary P sink in Lake 227. Eutrophication of the lake coincided with marked increases in the burial rate of total P (TP), as well as in the relative contribution of the NaHCO₃‐extractable P pool (humic‐bound P, P_Hum). Together, P_Hum and P_Org account for ≥70% of total P burial in the sediments deposited since artificial fertilization started. The P_Hum fraction likely comprises phosphate complexes with humic substances. The strong linear correlation between P and iron (Fe) extracted by NaHCO₃ implies a close association of the two elements in the humic fraction. Mössbauer and XANES spectra further indicate that most Fe in the post‐1969 sediments remained in the Fe (III) oxidation state, which is attributed to the stabilization of reducible Fe by organic matter, in part via the formation of phosphate‐Fe (III)‐humic complexes. Importantly, our results show that the eutrophication experimentation of Lake 227 caused the accumulation of a large reservoir of reactive sediment P, which may continue to fuel internal P loading to the water column once artificial fertilization is terminated.

中文翻译：

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加拿大安大略省实验湖区227湖人工富营养化后沉积磷埋藏的变化

自1969年以来，加拿大安大略省实验湖区（ELA）的227湖就开始施磷（P），导致磷从贫营养状态快速转变为富营养状态。从该氧化湖泊中收集到的沉积物岩心，以及这个独特湖泊的大部分为缺氧的沉积物，包含了在整个营养化转变过程中沉积物磷形态和埋藏率变化的历史记录。为了阐明这些变化，将化学萃取结果与²¹⁰ Pb沉积物测年以及³¹ P NMR，Mössbauer和XANES光谱学结合起来。1969年以前，有机磷（P _Org）是227湖的主要沉积P汇。湖泊的富营养化与总P（TP）的掩埋率显着增加，以及NaHCO _3可提取P池（腐殖质结合P ，P _Hum）。自开始人工施肥以来，P _Hum和P _Org占沉积物中总P埋葬的≥70％。P _Hum级分可能包含具有腐殖质的磷酸盐复合物。NaHCO ₃萃取的P与铁（Fe）之间的强线性相关暗示腐殖质部分中两个元素的紧密联系。Mössbauer和XANES光谱进一步表明，1969年后沉积物中的大多数Fe仍保持Fe（III）氧化态，这归因于有机物对可还原Fe的稳定作用，部分原因是通过形成磷酸盐-Fe（III）腐殖质。重要的是，我们的研究结果表明，湖227的富营养化实验导致大量反应性沉积物P的蓄积，一旦终止人工施肥，这可能会继续增加内部P向水柱的负荷。