Fundamental drivers of dissolved organic matter composition across an Arctic effective precipitation gradient

Abstract

The standard model for aquatic ecosystems is to link hydrologic connectivity to dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition and, ultimately, reactivity. Studies across effective precipitation gradients have been suggested as models for predicting how carbon cycling will change in Arctic aquatic ecosystems with projected drying (i.e., reduced hydrologic connectivity). To evaluate links between DOM dynamics and hydrologic connectivity, 41 stream samples from Greenland were analyzed across an effective precipitation gradient for DOM optical properties and elemental composition using ultrahigh‐resolution mass spectrometry. Sites with negative effective precipitation and decreased hydrologic connectivity exhibited elevated specific conductivity (SpC) and DOC concentrations as well as DOM composition indicative of decreased hydrologic connectivity, for example, lower aromaticity, assessed using carbon‐specific UV absorbance at 254 nm, decreased relative abundances of polyphenolic and condensed aromatic compounds, and increased relative abundances of highly unsaturated and phenolic compounds. Allochthonous inputs decreased as the summer progressed as exhibited by decreases in aromatic compounds. A decrease in molecular richness and N‐containing compounds coincided with the decrease in allochthonous inputs. DOC concentrations increased over the summer but more slowly than SpC, suggesting degradation processes outweighed combined evapoconcentration and production. The patterns in DOM composition suggest evapoconcentration and photodegradation are dominant controls. However, when hydrologic connectivity was high, regardless of effective precipitation, DOM reflected allochthonous sources such as snowmelt‐fed wetlands. These results highlight the challenges of modeling carbon cycling in aquatic ecosystems across effective precipitation gradients, particularly those with strong seasonality and regional variability in hydrologic inputs.

Using metacommunity ecology to understand environmental metabolomes

“…As a complement to α-diversity, β-diversity is commonly evaluated to capture multivariate differences among ecological communities. Previous studies have also used dendrogram-free βdiversity metrics (e.g., Jaccard) to study differences among metabolite assemblages 4,9,11 . As with α-diversity, these metrics can be extended by utilizing relational information provided by a phylogeny or dendrogram 23,24,42,48 .…”

“…As these studies increasingly become spatiotemporally resolved, an investigation of the underlying processes driving metabolome variability becomes necessary in order to develop transitive principles and enhance predictive capabilities across ecosystems. While many metabolomics studies have used multivariate methods to identify if differences exist between metabolomes [7][8][9][10][11][12] , they have limited capacity to reveal processes that constrain or promote variation [13][14][15] . Initial applications of ecological theory to NOM have revealed interlinkages between microbial community dynamics and molecular formula functional diversity [16][17][18] .…”

“…For example, differential abilities across taxa to scavenge nutrients can lead to a deterministic change in community structure through time 25 . Similarly, individual metabolites within metabolite assemblages will undergo fluctuations in production rate (analogous to birth rate) and degradation rate (analogous to death rate), driven by abiotic or biotic transformations 1,4,11,26 . Distinct from biological systems, however, metabolite 'death' is inherently coupled to metabolite 'birth' as one metabolite is transformed into another.…”

Differences in the Quantity and Quality of Organic Matter Exported From Greenlandic Glacial and Deglaciated Watersheds

“…Nonglacial streams in deglaciated watersheds drain local precipitation and active layer melt and therefore may contain meteoric water that becomes enriched in solutes following processes such as storage and chemical processing in the active layer or hyporheic zones, as well as OM derived from terrestrial or aquatic ecosystem productivity. Evapoconcentration may also contribute to the higher observed SpC and DOC concentrations in nonglacial streams because all deglaciated catchments in this study include lakes that are hydrologically connected to streams (Table 1; Anderson & Stedmon, 2007;Kellerman et al, 2019).…”

Organic Carbon Stabilization Mechanisms in Mangrove Soils: A Review

“…Mangrove soils are different from marine sediments in that there is a daily and seasonal fluctuation in salinity and that OM is mainly derived-from vascular plants (both mangroves and catchment plants). Vascular-plant derived aromatic materials (lignin, tannins) are known to be more susceptible to salinity-induced flocculation than microbial-derived aliphatic materials [75,78]. Hence, the role that salinity plays on C stabilization may be more important and spatiotemporally dynamic in vegetated coastal ecosystems including mangroves than in marine sediments.…”