Sources and biodegradability of dissolved organic matter in two headwater peatland catchments at the Marcell Experimental Forest, northern Minnesota,USA

Abstract

Where they are present in catchments, peatlands are a dominant source of dissolved organic matter (DOM) to surrounding waterways due, in part, to high production rates. Despite the preponderance of peatlands in northern latitudes and expected peatland vulnerability to climate change, little is known about peatland DOM degradation relative to a more comprehensive understanding of degradation when DOM is sourced from upland-dominated catchments. We compared DOM biodegradability of various sources of stream water in two catchments having peatlands (22%-33% of the area) surrounded by upland forests (70%-90% of the area, either deciduous or coniferous). We measured total organic carbon (TOC), and biodegradable dissolved organic carbon concentrations; bacterial respiration rates; streamflow; and upland runoff during and after snowmelt (March to June, 2009-2011). We also explored if DOM in upland runoff stimulated biodegradation of peatland-derived DOM (i.e., a priming effect), and if forest cover type affected DOM biodegradability. As expected, the peatlands were the largest sources of both water (72%-80%) and TOC (92%-96%) to the streams although more area in each catchment was in uplands (70%-90%). Several results were unexpected, yet revealing: (1) DOM from peatlands sometimes had the same biodegradability as DOM from uplands, (2) upland sources of DOM had negligible effects on biodegradability in the peatland and downstream, and (3) upland deciduous cover did not yield more degradable DOM than conifer cover. The most pronounced effect of upland runoff was dilution of downstream TOC concentrations when there was upland runoff. Overall, the effects of upland DOM may have been negligible due to the overriding effect of the large amount of biodegradable DOM that originated in bogs. This research highlights that peatland-sourced DOM has important effects on downstream DOM biodegradability even in catchments where upland area is substantially larger than peatland area. K E Y W O R D S bog hydrology, dissolved organic matter, DOM biodegradability, DOM sources, northern peatlands, source areas in upland-peatland catchments, upland forest This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Controls of Organic Carbon and Nutrient Export from Unmanaged and Managed Boreal Forested Catchments

“…Rich peatlands often are characterized by Carex peat, which releases more DOC than Sphagnum peat typical in poorer sites [52,53]. Fertile peatlands have been also found to be hotspots for TOC export in subarctic regions [54] and continental climates [32]. A positive correlation between peat coverage and TOC (or DOC) export is well known in many different environments [26][27][28][29]31,32], which was also apparent in our TOC models.…”

“…Fertile peatlands have been also found to be hotspots for TOC export in subarctic regions [54] and continental climates [32]. A positive correlation between peat coverage and TOC (or DOC) export is well known in many different environments [26][27][28][29]31,32], which was also apparent in our TOC models. Opposed to peatlands, mineral soils tend to retain DOC and therefore DOC concentrations in streams do not necessarily reflect the DOC release from organic matter [55].…”

“…Thus, all sources of DOC should be considered in the catchment level management [25]. Many studies have suggested that large part of the variation in DOC and TOC concentration in runoff can be explained by the peatland percentage in the catchment [26][27][28][29][30][31][32]. Other possible drivers for spatial and temporal variation in DOC leaching include temperature [23,33], runoff [23], and atmospheric sulfate and N deposition [34].…”

Peatland Dissolved Organic Carbon Export to Surface Waters: Global Significance and Effects of Anthropogenic Disturbance

“…Peatlands have been recognized as important sources of organic carbon transfer to surface water at the watershed scale (Laudon et al., 2011; Rosset et al., 2019; Sebestyen et al., 2021). Despite this, their global contribution to fresh waters and oceans is still speculative.…”

Long-Term Experimental Manipulation of Atmospheric Sulfate Deposition to a Peatland: Response of Methylmercury and Related Solute Export in Streamwater

“…27,28 The reference peatland is also surrounded by an alder lagg, but with less dense cover and smaller relative area than the S6 lagg at the experimental peatland. 15,28,30,31 The uplands of the S2 catchment are dominated by aspen (Populus tremuloides) with other mixed deciduous and coniferous species. 28 The centrally located peatlands dominate the hydrology of both catchments and all diffuse runoff generated within each catchment is first directed through the peatlands before exiting the catchments.…”