Can biogenic n-heptadecane be utilized to represent algae cell density dynamics in water environment? Evidences from...

The monitoring and prediction of algae cell density are the fundamental supports for eutrophication management. As the molecular marker of algae, n-heptadecane has been successfully utilized to reflect algae biomass in sedimentary studies. However, whether biogenic n-heptadecane (bio C₁₇) can be utilized to represent algae cell density dynamics in water environment still remains an issue. Current study aims to provide novel evidences from both field investigation and laboratory validation for it. Firstly, we found a strinkingly positive correlation between algae cell density dynamics and bio C₁₇ variations (p = 4.34 × 10^-10) via meta-analysis using field dataset in Lake Chaohu. Then, we selected Microcystis aeruginosa, Chlorella vulgaris and Melosira sp. as model species of cyanobacteria, green algae and diatom, respectively, for laboratory validation. Our results illustrated that n-heptadecane was synchronized with the growth for cyanobacteria and green algae but not for diatom. The association between bio C₁₇ and algae cell density was species-dependent, and the relationship between bio C₁₇ and cell density was linear within 10⁷ cells∙mL^-1. Therefore, we established and optimized a generalized additive model to fit observed algae cell density in Lake Chaohu. In the optimal model, bio C₁₇, Pielou evenness index J and Shannon-Wiener index H' were included, totally explaining 66% of the variance of algae cell density. Model comparisons revealed that considering algae community could indeed improve the interpretation of algae cell density in natural environment. In conclusion, our study provided novel evidences that bio C₁₇ can be utilized to represent the cell density dynamics of cyanobacteria and green algae in the environment.