Headwater streams and associated watersheds are highly relevant and responsive units of observation and management in terms of landscape-level drivers such as changes in land use/soils and climate forcing. Nevertheless, hydrologic indicators of alteration are rarely applied at such small scale, moreover in Chile, small watersheds (<10 km2) are poorly represented within the national hydrological monitoring network. We analysed two systems of indicators of hydrological alteration based on 2-6 years of high-frequency discharge observations, from a network of 12 small watersheds in western Chilean Patagonia, consisting of four sites representing a wide climatic gradient (precipitation 700-2000 mm/year), and evaluating within each group the effect of two land use conditions (reference and impacted sites). We found that the effects of land use changes on streamflow based on short-term datasets were more strongly linked to event dynamics with sub-daily indicators, compared to a lower predictive power of seasonal dynamics with daily indicators. Daily indicators were also important to evaluate changes in flows from land use, presumably a result of altered evapotranspiration regimes, with strongest effects in dry climate zones. We conclude with a proposal for a safe operating space in headwater stream catchments based on monitoring and early detection hydrological indicators, whose implementation would be relevance for public policies for mitigation of current and projected land use change.

Patagonia headwater streams, distinguished by ultra-low levels of inorganic nutrients and intact forested watersheds, are a potential global reference for intact stream communities and ecosystems in the temperate zone. Understanding steady state and dynamics of these remote stream ecosystems is challenged by near absence of visual or physical evidence of stream biofilm or phytobenthos. In order to understand biofilm community patterns and potential controls of climate regime and watershed land use, we conducted seasonal 16S rRNA metabarcoding of epilithic biofilm of nested zero to 2nd order forested stream networks. PCR amplification of 16S rRNA V4 region using dual-barcoded primers 16Sv4_515F and 16Sv4_806R revealed over 73,000 unique ASVs. Proteobacteria (mean 40.9% and 48.2% for respective dry and humid watershed clusters), were followed by Cyanobacteria (33.5% and 25.3% respectively), the latter surprising given the presumed forested/shaded heterotrophic reaches. While the full prokaryote diversity showed strongest responses to stream order, peaking in smallest 0-order reaches, cyanobacteria diversity responded to other landscape drivers such as climate regime, season and watershed intervention, with string seasonal peaks in winter and summer in 2nd order humid zone reaches, where riparian canopy loss results in a release from light limitation. Given the oligotrophic context, patterns in Cyanobacteria and functional taxa related to nitrogen cycling (e.g. Nitrosomonas) are also discussed. General conclusions on the Patagonian aquatic microbial observatory are presented, together with interpretation of a stream continuum concept for prokaryote and cyanobacteria stream microbiome in Patagonia.