Riparian vegetation is vital to the ecological integrity of stream ecosystems, regulating nutrient and sediment flow, stabilizing riverbanks, and moderating microclimate, all factors that influence primary production and periphyton communities. However, in tropical mountain regions, the ecological impacts of riparian degradation remain poorly documented. This study assessed how differences in land use and riparian cover affect environmental conditions, periphyton abundance, diversity, and diatom community composition in seven tropical mountain streams in southern Ecuador. Streams were sampled in forested, open (deforested), and degraded zones across a gradient of human disturbance. Water temperature and nutrient concentrations, particularly phosphates and nitrates/nitrites, were consistently higher in open and degraded sites. These conditions were not associated with greater periphyton abundance or diversity but with an increased prevalence of cyanobacteria, likely due to elevated light availability and temperature. Diatoms dominated the periphyton across all sites, with Gomphonema minutum, G. parvulum, and Achnanthidium minutissimum as the most abundant species. Diatom community composition in different land-use zones within the same stream was often as distinct as that observed between separate streams, underscoring the influence of fine-scale environmental variation over broader spatial patterns. The most degraded sites exhibited the most divergent diatom assemblages, reinforcing their value as sensitive indicators of ecological change. These findings highlight the need for conservation strategies that prioritize riparian vegetation protection, nutrient load reduction, and habitat heterogeneity. Diatom-based monitoring should be integrated into long-term ecological assessments to guide restoration efforts in increasingly threatened Andean stream ecosystems.
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