Nutrient Enrichment and Altered Temperature Regime Explain Litter Decomposition in Cold-Temperate Urban Streams

We evaluated the ecological integrity of Andean Patagonia urban streams by assessing changes in leaf litter decomposition rates and benthic invertebrate assemblage colonizing litter. Urban streams had higher nutrient concentrations and temperatures, and lower flow variability than cold-temperate oligotrophic Patagonia Andes streams. Leaf litter decomposition was faster in urban streams (50% higher than reference streams) mainly attributable to microbial decomposition; urban effect size in fine mesh (FM) bags was two-fold than in reference streams in coincidence with high nutrient concentrations and temperatures. Leaf litter decomposition had a similar effect in coarse mesh (CM) and FM bags, suggesting that invertebrate detritivore feeding activity was poor in urban streams. This was apparent when the effect of temperature on litter decay in CM bags was removed and urban effect size was nil. Invertebrates showed 71.5% dissimilarity between stream types, with higher tolerant species dominating urban streams. Functional feeding groups strongly varied between urban and reference streams over time, with shredders being the most contributing group in reference streams, and collector-gatherers, scrapers, and shredders contributing to urban streams. Our results highlight the avail of including functional studies to understanding the effect of human alterations on small streams complementing the analysis of ecosystem structure.