Sensitivity of river catchments to discharge-controlled dissolved carbon export: a study of eight catchments in southern Patagonia

Understanding the role of catchment sensitivity to dissolved carbon export to aquatic systems is crucial to predict future changes in carbon fluxes under changing climatic conditions. We present 1-year variations in dissolved organic (DOC) and inorganic carbon (DIC) concentrations and fluxes in eight river catchments differing in size (3–300 km2), morphology (steep to flat), and vegetation cover (grassland, forest and peatland) along a precipitation gradient in southern Patagonia, Chile. The results show large differences between catchments in terms of river DOC (2–47 mg L−1; 1–44 tons km−2 year−1) and DIC (0.1–38 mg L−1; 1–5 tons km−2 year−1) concentrations and fluxes in response to changes in discharge. Small and steep catchments hosting organic rich forest soils and peatlands were the most sensitive and showed the highest and fastest DOC release if evaluated on a per unit area basis. Here, rain events caused a rapid exponential increase in DOC release, while DIC export decreased exponentially. A negative correlation between DOC and DIC reveals the minor importance of DIC production through mineralization of DOC in most catchments. Catchments hosting large peatlands had low sensitivity to discharged controlled DOC release attributed to their high hydrological buffer capacity. Similarly, flat and relatively dry Patagonian steppe catchments have comparatively low sensitivity but have short-term high release of DOC accumulated during dry periods. In conclusion, morphology, rather than catchment size or vegetation cover, was found to show the major influence on sensitivity to DOC release.