Reflection on Aquatic SPM
The Diaz et al (2020) paper presented by Group 6 raised many interesting questions about suspended particulate matter (SPM) and eDNA. I was definitely excited by this study and the idea that SPM can be a source for high eDNA yields. As I plan my upcoming surveys for rare bridle shiners, I have become interested in using sediment samples along with water-column samples to try to detect the minnows in water bodies. But our class discussion raised questions about the article that are also highly relevant to my project, such as: How much of the SPM is simply re-suspended from sediment? How long does it take for eDNA to degrade in a sediment trap? What sediment trap design would be best for sunny, shallow waters with little current? How do sediment and SPM characteristics affect eDNA quality/yield? It could be that SPM collection is not viable in certain habitats because it is impossible to fully separate re-suspended benthic sediments from more “contemporary” SPM. This raises another question about time scale: for certain projects, it may not matter that re-suspended DNA from a few months or years ago is contained in the sample. When surveying for extremely rare species, a trade-off may exist between obtaining water samples with lower, but more recent, eDNA yields, and sediment or SPM samples with higher yields of eDNA of unknown age. The higher yield may increase detection probability, but the organisms were not necessarily present at the time of sample collection.