Effects of preservatives and poisons on the elemental and isotopic composition of freshwater particulate organic matter

Sediment traps, often used in tandem with preservatives or poisons, are widely used for the collection of particulate organic matter (POM), providing insight into the source to sink mechanisms that shape major biogeochemical cycles and sedimentary carbon sequestration. The effectiveness of these treatments has been studied for marine POM, but is poorly constrained for freshwater POM, whose molecular composition differs due to greater terrigenous input. We tested four treatments commonly used in marine sediment traps, along with untreated controls, over a 1‐yr period to assess their ability to retain original elemental and isotopic compositions of organic carbon (%TOC and δ 13 C org ) and nitrogen (%TN and δ 15 N) in POM collected from a freshwater pond (Willow Pond, Michigan, USA). Consistent with marine studies, 0.005% (w/v) mercuric chloride was the most effective in preserving both C and N geochemical signatures across the 1‐yr incubation period. Untreated samples also maintained original POM geochemical signals but only for approximately 6 months, providing an inexpensive, nontoxic alternative that can be used for shorter deployment or storage periods.