Assessing the chemistry and bioavailability of dissolved organic matter from glaciers and rock glaciers

Abstract

As glaciers thaw in response to warming, they release dissolved organic matter (DOM) to alpine lakes and streams. The United States contains an abundance of both alpine glaciers and rock glaciers. Differences in DOM composition and bioavailability between glacier types, like rock and ice glaciers, remain undefined. To assess differences in glacier and rock glacier DOM we evaluated bioavailability and molecular composition of DOM from four alpine catchments each with a glacier and a rock glacier at their headwaters. We assessed bioavailability of DOM by incubating each DOM source with a common microbial community and evaluated chemical characteristics of DOM before and after incubation using untargeted gas chromatography mass spectrometry based metabolomics (GC-MS). Prior to incubations, ice glacier and rock glacier DOM had similar C:N ratios and chemical diversity, but differences in DOM composition. Incubations with a common microbial community showed DOM from ice glacier meltwaters contained a higher proportion of bioavailable DOM (BDOM) and resulted in greater bacterial growth efficiency (BGE). After incubation, DOM composition from each source was statistically indistinguishable. This study provides an example of how MS based metabolomics can be used to assess effects of DOM composition on differences in bioavailability of DOM. Furthermore, it illustrates the importance of microbial metabolism in structuring composition of DOM. Even though rock glaciers had significantly less BDOM than ice glaciers, both glacial types still have potential to be important sources of BDOM to alpine headwaters over the coming decades.Key PointsBioavailability of organic matter released from glaciers is greater than that of rock glaciers in the Rocky Mountains.The use of GC-MS for ecosystem metabolomics represents a novel approach for examining complex organic matter pools.Both glaciers and rock glaciers supply highly bioavailable sources of organic matter to alpine headwaters in Colorado.

Resource heterogeneity structures aquatic bacterial communities

“…To estimate resource heterogeneity, we characterized the composition of extractable DOM for each lake using ecosystem metabolomics [53][54][55]. We extracted DOM from each sample using solid phase extraction (SPE), which is able to recover 40-60% of the total DOM based on chemical sorption properties [56].…”

Persistent Nitrate in Alpine Waters with Changing Atmospheric Deposition and Warming Trends

“…Alpine surface water [NO 3 − ] remain elevated, despite proportional declines in atmospheric [NO 3 − ], implicating the role of nitrification of new reduced N sources. Rock and snow glaciers supply dissolved organic matter that varies in quality and quantity in high-elevation alpine lakes, 87 which can provide additional NH 4 + substrate upon remineralization. Rock glacier source waters contribute ∼89−97% of the NO 3 − exported by surface waters throughout the summer season in these systems with significant declines observed in rock glacier-fed surface waters at varying seasonal and decadal time scales compared to snow glacier-fed surface waters (Figure 3 and Table S12).…”

Biogeochemical Dynamics of a Glaciated High‐Latitude Wetland

“…However, the high organic matter content may be responsible for the increased taxonomic diversity characterized close to glaciers (RHM organic matter >30%) and in areas of high organic matter content (LIL surface sediments organic matter >10%). High organic matter likely facilitates biotic mineralization by providing chemical diversity and labile compounds (Braeckman et al., 2021; Fegel et al., 2019; Hood et al., 2009; Tanentzap et al., 2019). However, the sustained high levels of organic matter despite the diverse microbial community hints at a lack of significant biotic degradation, likely supporting the possibility for mineral protection or recalcitrant available carbon and highlighting the need for further studies.…”