Riverine detritus is a key nutritional resource for benthic consumers, yet its biochemical quality fluctuates rapidly and is poorly captured by bulk indicators such as elemental analysis. To improve assessment sensitivity, we compared two analytical approaches targeting organic nitrogen. We refined a fluorimetric assay for primary amines using o-phthalaldehyde (OPA), identifying 2 M KCl as an optimal extraction medium that maximizes recovery while minimizing matrix interference. In parallel, we optimized capillary electrophoresis with contactless conductivity detection (CE-C4D) for free amino acid determination using 0.4 M ammonium carbonate. Applied to detritus from multiple river sites and seasons, both methods showed that primary amines and amino acids vary by an order of magnitude more than total nitrogen and exhibit patterns not detectable by elemental analysis, with consistent temporal trends across catchments. Primary amine-based measurements therefore provide a more sensitive and ecologically relevant assessment of detrital nutritional quality than bulk nitrogen metrics. The OPA assay is well suited for routine monitoring due to its simplicity and robustness, whereas CE-C4D enables detailed compositional profiling where amino acid speciation is required. Overall, detrital quality reflects both intrinsic properties and recent hydrological conditions, underscoring the importance of antecedent discharge and precipitation dynamics in its interpretation.
Ječmen et al. (Thu,) studied this question.