An Investigation of Surface Water Sediment Source Tracking Using Bacterial Metagenomics and Elemental Fingerprinting

Excess suspended sediment in river systems commonly degrades surface water quality. A sediment source tracking approach is necessary to target management practices that will reduce significant sources of sediment in rainfall runoff and restore water quality. Sediment source tracking utilizes the biogeochemical characteristics of sediment, often paired with a mathematical model, to link eroding source materials and in-stream suspended sediment. However, there are still many questions left unanswered in using this approach, including simultaneously identifying fecal contamination sources, quantifying the reliability of sediment tracers, and methods to assess the accuracy of sediment source identification. The research herein utilized the microbial communities and elemental fingerprinting techniques associated with an impaired watershed’s eroding source materials and suspended sediment; these sediment source tracking methods were employed using two Bayesian-based models, SourceTracker for metagenomic bacterial community data, and Stable Isotope Analysis in R (SIAR) for the sediment elemental composition. Bacterial metagenomic data from sources of both upland eroding soil (i.e., cropland and cattle paths) and eroding bank soil were more similar to the bacterial metagenomic community within in-stream suspended sediment than manure; this indicates that certain microbial communities in upland eroding soils can be used to identify important sources of instream suspended sediment. Eroding source material elemental composition data indicated that bank erosion was an important source of suspended sediment within the watershed. This knowledge can be used to more efficiently improve water quality by focusing on stream bank stabilization projects. Additional research herein evaluated the performance of nitric acid extraction versus total dissolution for sediment elemental analysis; the results clearly showed that the safer nitric acid extraction provided an elemental analysis that was as effective for sediment source tracking as total dissolution with hydrofluoric acid.