We inferred paleoenvironmental conditions in Lake Inawashiro-ko, Japan, over the past 1700 years, using diatom assemblages in the uppermost 2 m of sediment core INW2012. The core was characterized by three diatom zones: Zone 3 (302–1556 CE) was dominated by the planktonic taxon Aulacoseira nivalis; Zone 2 (1556–1991 CE) was predominantly planktonic Cyclotella radiosa and Aulacoseira subarctica; Zone 1 (1991–2012 CE) had highest relative abundance of Fragilaria neoproducta, accompanied by Cyclotella radiosa and Aulacoseira subarctica. Correlations between recorded diatom assemblages and water quality in previous studies enabled us to infer past environmental conditions, which indicate the lake became more eutrophic over the past ~ 30 years. Support for this inference comes from the predominance of benthic Fragilaria neoproducta in the limnetic assemblage of Zone 1. The habitat of F. neoproducta expanded from the littoral zone to offshore areas as a result of progressive eutrophication. The diatom record also suggests that alkalization of Lake Inawashiro-ko occurred over the past 1700 years. If, however, most production took place in the littoral zone, past pH values throughout much of the lake may have been lower than those indicated by the diatom assemblages. This points to the need for more diatom-based paleoenvironmental studies in lakes that display a broad range of environmental conditions across space, i.e. from the littoral to the limnetic zone.

我们使用 INW2012 沉积岩心最上层 2 m 中的硅藻组合推断了过去 1700 年来日本猪苗代湖的古环境条件。核心的特征是三个硅藻区：第 3 区（公元 302-1556 年）以浮游分类群Aulacoseira nivalis 为主；Zone 2 (1556–1991 CE) 主要是浮游小环藻和Aulacoseira subarctica；区域 1（1991-2012 CE）具有最高相对丰度Fragilaria neoproducta，伴随着Cyclotella radiosa和Aulacoseira subarctica. 先前研究中记录的硅藻组合与水质之间的相关性使我们能够推断过去的环境条件，这表明湖泊在过去 ~ 30 年中变得更加富营养化。对这一推论的支持来自于底栖Fragilaria neoproducta在区域 1 的湖沼组合中的优势。F. neoproducta的栖息地由于逐渐富营养化，从沿海地区扩展到近海地区。硅藻记录还表明猪苗代湖在过去 1700 年间发生了碱化。然而，如果大部分生产发生在沿海地区，那么过去整个湖泊大部分地区的 pH 值可能低于硅藻组合所显示的值。这表明需要在湖泊中进行更多基于硅藻的古环境研究，这些湖泊显示了整个空间的广泛环境条件，即从沿海到湖沼区。