An Integrated Assessment of Dissolved Organic Matter and Catchment Characteristics in Northern Patagonian Headwater Streams

ABSTRACT

Headwater streams are critical ecological corridors that regulate hydrological and biogeochemical fluxes across landscapes, yet remain underrepresented in global datasets. In this study, we present one of the first integrated assessments of morphometric attributes, physicochemical conditions and dissolved organic matter (DOM) composition in minimally disturbed catchments of Andean Patagonia. Using GIS‐based morphometric analysis, in situ water chemistry and advanced optical characterization of DOM, we examined 29 streams in northwestern Patagonia, all situated within Nahuel Huapi National Park (NHNP) and influenced by the urban conglomerate of San Carlos de Bariloche, Dina Huapi and Villa La Angostura. Catchments displayed high morphometric heterogeneity with basin size and slope emerging as key drivers of hydrological response. Principal component analysis distinguished three basin types, which explained systematic differences in stream temperature, electrical conductivity (EC) variability and discharge regimes. Despite this geomorphic diversity, DOM composition was remarkably consistent across streams, dominated by humic fractions of terrestrial origin. Fluorescence indices revealed low autochthonous production and high humification, underscoring the primacy of soil‐derived inputs in these ultra‐oligotrophic systems. Temporal comparisons between 2017 and 2024 revealed significant warming and reduced streamflow, coupled with a sustained decline in chromophoric DOM components, while bulk DOC concentrations remained stable. These findings highlight the sensitivity of DOM quality to climate‐driven hydrological shifts. Urbanization effects were subtle but detectable: even low levels of basin development increased signals of freshly produced organic matter, suggesting early biogeochemical alteration. Our results establish critical baseline data for Patagonian headwaters. By documenting both natural variability and early signals of change, this study contributes to global efforts to understand hydrological vulnerability under climate and land‐use transformations, and underscores the importance of mountain headwaters as sentinels of environmental change.