Autochthonous calcite precipitation is an important process for C-fixation in hard-water lakes, which is mainly induced by the photosynthesis of planktonic microorganisms. Among these, the widespread calcifying green alga Phacotus lenticularis (Ehrenberg) Diesing contributes to biogenic calcite precipitation in temperate regions. Its role in carbonate precipitation needs to be investigated, because there are no studies dedicated to the quantitative contribution of Phacotus shells to long term carbonate sequestration in hard-water lake sediments. In order to fill this gap, the Phacotus shell content in the sediments of four German hard-water lakes was determined and compared to the fraction of Phacotus shells in the total suspended autochthonous calcite of the euphotic zone.
It was found that the Phacotus shells contributed at least 10% to the autochthonous carbonate precipitation in the upper water column in three investigated lakes. During a Phacotus mass occurrence with a cell density of 1.8 × 106 Ind L-1 in Lake Hopfensee, even 59% of the 3.6 mg L-1 total carbonate concentration consisted of Phacotus shells. In contrast to this high amount, the topmost basinal sediment contained a Phacotus shell content between 80 and 36,252 individuals per mg dry sediment, representing only 0.02% to 2.28% of the total carbonate sediment content. In a gravity core from Lake Grosser Ostersee, dating back ~150 years, the Phacotus shell content was continuously below 0.24% whereas the shell diameters remained equal to those of living individuals found in the water column proving that Phacotus shells are capable to persist in the sediment after deposition.
A main reason for the large discrepancy between Phacotus shell abundance in the euphotic zone and in sediment was found to be the gross authigenic carbonate precipitation, which dilutes the sedimenting Phacotus shells that accumulate exclusively during short and intensive population peaks in summer. Additionally, dissolution of the carbonate shells during sedimentation was proven to be a relevant factor in Lake Igelsbachsee by means of reducing the number of Phacotus shells reaching the lake bottom. These facts explain that short-term high Phacotus carbonate contents of the total suspended carbonate in the water column do not mirror the contribution of Phacotus shells in the sedimentary record.

方解石的自生沉淀是硬水湖泊中固碳的重要过程，其主要由浮游微生物的光合作用引起。其中，广泛钙化的绿藻（Pharmatus lenticularis）（Ehrenberg）染色有助于温带地区的生物方解石沉淀。需要研究其在碳酸盐沉淀中的作用，因为没有专门研究Phacotus壳对硬水湖沉积物中长期碳酸盐固存的定量贡献的研究。为了填补这一空白，确定了四个德国硬水湖沉积物中的Phacotus壳含量并将其与Phacotus的分数进行比较炮弹位于常光区总悬浮的方解石中。
发现在三个被调查的湖泊中，Phacotus贝壳至少占上水柱中碳酸盐碳酸盐沉淀的10％。在霍普芬湖湖中发生密度为1.8×106 Ind L-1的Phacotus大块事件期间，在3.6 mg L-1的总碳酸盐浓度中，甚至有59％由Phacotus贝壳组成。与如此高的数量相比，最上层的盆地沉积物每毫克干沉积物包含80-36,252个人的Phacotus壳含量，仅占总碳酸盐沉积物含量的0.02％至2.28％。在从湖格罗瑟Ostersee重力核心，距今〜150多年来，Phacotus壳的含量连续低于0.24％，而壳的直径仍与在水柱中发现的活着的个体的直径相等，这证明了Phacotus壳能够在沉积后保留在沉积物中。人们发现，富营养区和沉积物中Phacotus贝壳丰度
之间存在巨大差异的主要原因是自生碳酸盐的总沉淀，这稀释了仅在夏季人口密集和密集的高峰期堆积的沉淀的Phacotus贝壳。此外，通过减少Phacotus的数量，证实了沉积过程中碳酸盐壳的溶解是伊格斯巴赫湖的一个相关因素。贝壳到达湖底。这些事实说明，短期高Phacotus在水柱的总悬浮碳酸盐的碳酸盐内容不反映的贡献Phacotus壳中沉积记录。