Abstract
Environmental DNA (eDNA) analysis has increasingly been used for aquatic biomonitoring, although interpretation of results needs to consider how environmental factors influence the degradation process of eDNA. This review focuses on pH, which has long been considered a key factor in eDNA degradation although its apparent effect on eDNA degradation has varied across studies. Here I present a synthesis of existing research that summarises what is so far known about the pH dependence of eDNA degradation, and a meta-analysis that demonstrates a nonlinear, upward convex relationship between eDNA decay rates and pH, with modelled eDNA decay rates peaking around pH 8. These results suggest that under slightly alkaline conditions, which are often considered suitable for DNA preservation, eDNA degradation may be accelerated by the promotion of microbial and enzymatic activity. On the other hand, there were substantial inter-study discrepancies in the dataset, suggesting that the present meta-analysis could not fully address the complexity of pH-dependent eDNA degradation. I end this review with an extensive discussion of some possible mechanisms that should be further investigated in order to achieve a more comprehensive understanding of the pH dependence of eDNA degradation. These efforts will help with more accurate predictions of the persistence time and decay rates of eDNA under various environmental conditions, thereby potentially improving our interpretations of eDNA-based biodiversity surveys.