Long-Term and Seasonal Trends in the Mode of Accumulation of Elements in the Bodies of Aquatic Insect Larvae

Aquatic insect larvae in high mountain streams reflect natural changes in water chemistry, making them effective bioindicators of ecosystem health. Changes in element accumulation in the bodies of larvae from the functional feeding groups scrapers and predators were monitored over a 5-year period (2019-2023). We aimed to evaluate long-term and seasonal trends in the accumulation of selected elements and to assess whether these patterns were linked to hydrological conditions or reflected post-disturbance recovery. Element concentrations were measured using ED-XRF spectrometry. Principal component analysis was used to identify accumulation patterns and their relationships with water flow rate and total dissolved solids (TDS). In scrapers, principal component (PC) 1 indicated general element accumulation, which varied significantly by year and season. PC2 showed increased in iron, copper, zinc, and lead with decreased in phosphorus and sulphur, with significant seasonal variation. PC3 linked an increase in iron and barium with higher flows and reduced chlorine and TDS, showing notable variation across years and seasons. In predators, PC1 also represented general element accumulation but involved fewer elements than scrapers. PC2 showed increased chromium and copper with higher flows and lower TDS, and PC3 indicated increased sulphur with higher flow and decreased zinc. Unlike scrapers, predators did not exhibit significant interannual variation, though seasonal variations were evident. These findings suggest that scrapers are more responsive to long-term environmental changes, while seasonal accumulation patterns in both groups are influenced by stream flow, food availability, and physiological changes during ontogeny.