Effect of salinity and water dilution on environmental DNA degradation in freshwater environments

Environmental DNA (eDNA) analysis methods have been developed to detect the distribution and abundance/biomass of organisms in various environments. eDNA generally degrades quickly, thus the study of eDNA degradation is critical for eDNA evaluation. However, there have only been a few studies of eDNA degradation experiments in which the salt concentration and water dilution were controlled. In this study, the effects of degradation were experimentally evaluated by controlling the salinity and water dilution of pond water. An experiment was conducted to evaluate the effects of salinity and dilution on eDNA detection with fragmental eDNA and free cell-derived eDNA using pond water, diluted pond water, and saline pond water. We quantified the eDNA copies of free cells, fragmental DNA, and the eDNA from Cyprinus carpio. In both the diluted and saline pond water, we found that the degradation rate of eDNA was much slower than that in pond water. Furthermore, the DNA concentration did not exponentially decrease in both the saline purified water and purified water samples. For the lower degradation rate in salt water, we interpreted that salts may affect DNA degradation factors such as microbe compositions and activities. The effect of salinity and dilution on eDNA detection provides fundamental information about the degradation process of eDNA, which is essential to understand the behavior of eDNA in natural environments.