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Best Practices for Organic Matter Analysis in Aquatic Systems

Learn essential techniques for analyzing organic matter content in water, including high-temperature combustion and element analysis. Discover tips for sample collection, filtration, and validation to ensure accurate results. Proper intercalibration and consistency between sites are emphasized.

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Best Practices for Organic Matter Analysis in Aquatic Systems

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  1. Organics WG POM: (umol / kg) BestPC and PN : High Temp Combustion via Elemental Analyzer POP: Ash Hydrolysis Collection: Volume filtered is site dependent Best: separate bottle dispensed into carboy that can be mixed and sampled to avoid bias against rapidly sinking particles. Good: subsample bottle – esp in oligotrophic systems Some sites- prescreen through 200 µm mesh Filtration: pay attention to filtration rate and avoid overloading filter. Best- low vacuum (5 in Hg), positive pressure filtration

  2. POM: PC&PN Sample prep: when drying sample be careful of oven temperature as drying at 70° C can result in N loss For Carbon: Best: run total C and PIC directly to assess POC Good: acidify (fume) to rid sample of PIC - Validate Intercalibration: Best: collect and prepare “in house” references from local system • Run in every run multiple time in a run • Swap with other TS for intercalibration Good: use other references like apple leaf for recovery checks

  3. DOM (umol /kg): DOC: Best: High Temperature Combustion (black art) Good: Persulfate Oxidation Acceptable: UV oxidation TDN: Best: High Temperature Combustion –Gives TDN must subtract out DIN. Problems when NO3 is too high due to propagation of error Good: Persulfate Oxidation Acceptable: UV oxidation DOP: BestPersulfate Oxidation Good/ acceptable: UV oxidation - problem with Si interference

  4. DOM: Filtering is recommended in coastal systems with high POC load. Oligotrophic systems POM load is small and TOM may be appropriate. Collection: Minimize handling Best- when filtering best to be conducted directly off Niskin through combusted GF/F in PC cartridge using silicone tubing…no Tygon! Combusted Glass or acid leached HDPE bottle Freeze at -20 up right or acidify to pH 3 and refrigerate good- subsample and filter in lab. Take special care to minimize contamination!!

  5. Intercalibration & Consistency between Sites: There is no certified reference material but Hansell Consensus ref Material are available. Best/ must: Make 2 – 3 large volume (8 – 10 L) in house References that are calibrated against the Hansell Consensus Material. These in house references along with blank water should be run every 8- 10 samples to assess performance of the analytical run. References should not vary by more than 2 – 3 % over the course of an acceptable run When introducing new “in house” references- analysts need to overlap reference batches. These references can be swapped among TS for intercalibration of analysis.

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