Pollution effects on diversity and content of the stable isotope 15N in macroinvertebrates: a study of the impacts on the functional groups from the Maipo River, Chile

Context Anthropogenic activities producing nitrogen have affected freshwater ecosystems. The δ15N isotope is a key indicator of these impacts. Macroinvertebrates are vulnerable to pollution. Studying the macroinvertebrate functional feeding groups (FFGs) helps us understand the structure, function and balance of fluvial ecosystems, and how pollution alters ecosystem dynamics. The Maipo River Basin is one of the most polluted in Chile. Aims This study examines how pollution affects macroinvertebrate family diversity, FFGs, δ15N content and trophic position. Methods Using a Surber net, five replicates were taken from two polluted and two non-polluted sites to analyse diversity at the family and FFGs levels. Differences in δ15N content and FFGs trophic position were assessed using a permutation Student’s t-test. Key results Gathering–collectors inhabiting polluted sites showed less richness of taxa than they did in the non-polluted sites. δ15N contents were higher in polluted sites, although gathering–collectors had a lower trophic position. Conclusion Our results indicated that greater nitrogen input creates conditions that may affect the diet of studied organisms, potentially explaining the observed trophic position changes. Implications Pollution alters the composition and structure of macroinvertebrate communities by affecting FFG diversity. This should be considered in future management plans.