Variability in Dissolved Organic Matter Composition and Biolability across Gradients of Glacial Coverage and Distance from Glacial Terminus on the Tibetan Plateau

Abstract

Globally, alpine glaciers hold a large quantity of dissolved organic matter (DOM) and are headwaters of numerous rivers supporting downstream heterotrophic metabolism. However, it remains unclear how glacial coverage and distance from the glacial terminus affect the fate of DOM. Here, we elucidate DOM variability in glacial-fed streams on the Tibetan Plateau using field sampling and bioincubation experiments and compare our findings with the existing literature. We found that dissolved organic carbon, DOM absorption a(254), DOM aromaticity, and the relative abundance of lignin compounds in glacial-fed streams and rivers all increased with increasing distance from the glacial terminus and with decreasing glacial coverage. We also found that contribution of protein-like components, the relative abundance of aliphatic compounds, and DOM biolability increased with increasing glacial coverage and with decreasing distance from the glacial terminus. The ratio of glacial coverage to the logarithmic transformed distance from the glacial terminus was better than that of actual glacial coverage and distance from the glacial terminus in tracing the variability of glacial-fed stream DOM. Microbes in surface ice can produce biolabile DOM that is exported downstream with meltwater. This glacial-fed stream and river DOM is an important source of the highly bioavailable material fueling downstream heterotrophic activity.

The evolution of stream dissolved organic matter composition following glacier retreat in coastal watersheds of southeast Alaska

“…Concurrently, stream DOM composition became increasingly dominated by terrestrial plant and soil signatures (Table 1, Figures 3 & 4). The observed trends in the streamwater DOM composition with glacier retreat were consistent with previous studies that assessed watersheds with gradients in glacier cover, where low glacier cover was associated with more enriched bulk Despite the ancient aliphatic signature of DOM being a ubiquitous feature of glaciers and their environments, the sources of OM that explain glacier outflow DOM composition remain uncertain (Behnke et al 2020;Bhatia et al 2013;Kellerman et al In Press;Lawson et al 2014b;Singer et al 2012;Spencer et al 2014a;Stubbins et al 2012;Zhou et al 2019a (Behnke et al 2020;Koch and Dittmar 2006). Thus, significant contributions of OM from overridden, subglacial palaeoorganic material are unlikely.…”

“…14 C-DOC values(Fellman et al 2014; Hood et al 2009;Zhou et al 2019a) and DOM that contained a large proportion of organic matter (OM) from fresh plant biomass and soil organic material (i.e.,  13 C-DOC depletion and increased % RA of aromatics and HUPs).…”

How hydrology and anthropogenic activity influence the molecular composition and export of dissolved organic matter: Observations along a large river continuum

“…Rapid microbial use of bio-labile organic carbon in the river may have occurred and may have driven the higher aromaticity of dissolved organic matter in the Yangtze River in comparison to other large rivers of the world; this being supported by the laboratory bio-incubation experiment. A fraction of the carbon was found to be bio-available with a bioavailable DOC of 12-18% over 28 d of bio-incubation in the Yangtze River, which is comparatively lower than in small coastal temperate streams (Fellman et al 2008) and permafrost-fed (Abbott et al 2014) and glacial-fed stream ecosystems (Spencer et al 2014;Zhou et al 2019). The Yangtze River watershed has experienced rapid urbanization during the past three decades and the river now faces numerous eco-environmental challenges.…”

Seasonal Variations of Dissolved Organic Matter by Fluorescent Analysis in a Typical River Catchment in Northern China

“…Transport of terrestrial DOM is generally dependent on steady flow dynamics in flow path/runoff [7,33], and rainfall is seasonal and highly varied in Duliujian River catchment. It was reported that in glacial-fed rivers, DOC, a 254 and aromaticity were enhanced corresponding to the increasing distance from the glacial terminus, which was controlled largely by glacial or snow meltwater [44]. Two aspects (rainfall and buffer distance from water source) were considered to utilize spatial geographic analysis techniques to probe the effect of land use on organic matter in the catchment.…”