Our understanding of water-soluble organic constituents and their transformation in the unique aqueous continuum over cryosphere region is scarce. Here, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and dissolved total nitrogen (DTN) and water-soluble inorganic ions in multiple water bodies from the eastern Tibetan Plateau (TP) cryosphere are systematically determined from a suite of field campaigns, laboratory experiments, linear regression analysis, and multiple comparisons, etc. We found that the water bodies located at high elevation have much lower DOC contents compared to the samples at lower elevation, there has significant altitude dependence of DOC abundance in water bodies over the study area (elevation range: 1971-4700 m asl). Comparison of optical properties, source apportionment, chemical analysis and model simulation of the water bodies provide evidence that the atmospheric deposition of organic species in high mountains is transported to plateau lakes in the northeast of TP via alpine runoff (45%) and snow/ice meltwater (20%). Further, dominance of anthropogenic activities in lower elevations can contribute (35%) to the observed altitudinal dependency. Thus, this preliminary study represents the first systematic investigation of the transport and cycling of organic carbonaceous matter and nitrogenous matter in eastern TP and warrants more robust in-situ observations and measurements in future in High Mountains of Asia.

Predicting the response of dissolved nitrogen export from Arctic watersheds to climate change requires an improved understanding of seasonal nitrogen dynamics. Recent studies of Arctic rivers emphasize the importance of spring thaw as a time when large fluxes of nitrogen are exported from Arctic watersheds, but studies capturing the entire hydrologic year are rare. We examined the temporal variability of dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) concentrations in six streams/rivers in Arctic Alaska from spring melt to fall freezeup (May through October) in 2009 and 2010. DON concentrations were generally high during snowmelt and declined as runoff decreased. DIN concentrations were low through the spring and summer and increased markedly during the late summer and fall, primarily due to an increase in nitrate. The high DIN concentrations were observed to occur when seasonal soil thaw depths were near maximum extents. Concurrent increases in DIN and DIN-to-chloride ratios suggest that net increases from nitrogen sources contributed to these elevated DIN concentrations. Our stream chemistry data, combined with soil thermistor data, suggest that downward penetration of water into seasonally thawed mineral soils, and reduction in biological nitrogen assimilation relative to remineralization, may increase DIN export from Arctic watersheds during the late summer and fall. While this is part of a natural cycle, improved understanding of seasonal nitrogen dynamics is particularly important now because warmer temperatures in the Arctic are causing earlier spring snowmelt and later fall freezeup in many regions.