Effectiveness of preservatives and poisons on sediment trap material in freshwater environments

To estimate the effectiveness of preservative/poisons on sediment trap material in freshwater environments, we measured the ratio of particulate organic matter retention [particulate organic carbon (POC) and nitrogen (PON), particulate phosphorus (PP)] using simulated sediment trap material (SSTM). SSTM was collected in summer and fall from depths of 30 and 85 m in the mesotrophic northern basin of Lake Biwa, Japan. All SSTM was incubated in buffered formalin, sodium azide (NaN) and mercuric chloride (HgCl) solutions for a period of 56 days. The retention ratio of POC, PON and PP of SSTM was measured throughout the course of the experiments. Results showed that buffered formalin and HgCl were very effective in preserving POC. Although NaN was less effective at preventing degradation of POC, the degradation process as a function of time was described with the double-exponential decay equation extremely well. Buffered formalin and HgCl were also effective in preserving PON, but less effective than for POC. To ensure accurate measurements of PON vertical flux, therefore, one should estimate the decomposition kinetics of PON in sediment trap material. None of the preservatives used in this study was effective for preserving PP, which was rapidly degraded within a week. However, the degradation process was also fully described by the equation, and this will make it possible to accurately estimate PP vertical flux.