The effect of long-term water table manipulations on dissolved organic carbon dynamics in a poor fen peatland

Abstract

Dissolved organic carbon (DOC) production, consumption, and quality displayed differences after long-term (~55 years) hydrological alterations in a poor fen peatland in northern Michigan. The construction of an earthen levee resulted in areas of a raised and lowered water table (WT) relative to an unaltered intermediate WT site. The lowered WT site had greater peat aeration and larger seasonal vertical WT fluctuations that likely elevated peat decomposition and subsidence with subsequent increases in bulk density, vertical hydraulic gradient, decreased hydraulic conductivity (K sat ), and a greater pore water residence time relative to the unaltered site. The raised WT site displayed a decreased K sat combined with seasonal upwelling events that contributed to a longer residence time in comparison to the unaltered site. These differences are potentially contributing to elevated DOC concentrations at the lowered and raised WT site relative to the unaltered site. Additionally, spectrophotometric indices and chemical constituent assays indicated that the lowered site DOC was more aromatic and contained elevated concentrations of phenolics compared to the intermediate site. The raised site DOC was less aromatic, less humified, and also had a greater phenolic content than the intermediate site. Furthermore, an incubation experiment showed that DOC in the raised site contained the greatest labile carbon source. Based on our results, long-term WT alterations will likely impose significant effects on DOC dynamics in these peatlands; however, WT position alone was not a good predictor of DOC concentrations, though impoundment appears to produce a more labile DOC whereas drainage increases DOC aromaticity.

Hydrological control of dissolved organic carbon dynamics in a rehabilitated <i>Sphagnum</i>–dominated peatland: a water-table based modelling approach

“…In addition, the difference in [DOC] dynamics is also reflected in DOM quality inferred from its fluorescence properties, with a greater increase in low molecular weight compounds (component M) and fewer aromatic high molecular 5 weight compounds (component C) in the rewetted location during the dry season compared to the control area. These findings are in agreement with the studies by Höll et al (2009), Hribljan et al (2014 and Strack et al (2015) who observed that wetter sites would result in a pore water with smaller and fewer aromatic dissolved organic molecules (likely sourced from inputs of fresh litter from growing vegetation) than the sites with a lower water table.…”

“…In addition, anaerobic conditions in the rewetted site would lead to less efficient decomposition of organic matter, increasing the production of water-soluble intermediate metabolites (Kalbitz et al, 2000;Strack et al, 2008). An increase in [DOC] in the rewetted location can also be explained by an increase in the photic zone, potentially supporting algae photosynthate production enhancing DOC release into the water column, as suggested by Hribljan et al (2014). However the latter hypothesis is the 25 least probable in our case since no ponding water is observed in summer in the study area.…”

“…Long-term studies have reported decreasing pore water [DOC] more than 10 years after a restoration operation took place (Höll et al, 2009;Wallage et al, 2006), while others observed increasing [DOC] after restoration (Hribljan et al, 2014;30 Strack et al, 2015). Glatzel et al (2003) predicted a decrease in [DOC] with time due to a depletion of easily decomposable organic matter in the peat.…”

“…DOC dynamics in peatlands has been found to be strongly controlled by site hydrology, especially by the water table 5 depth (WTD) (e.g. Hribljan et al, 2014;Jager et al, 2009;Strack et al, 2008Strack et al, , 2015. Therefore, hydrological disturbances such as drainage can lead to increased DOC exports in relation with WTD variations (Strack et al, 2008;Worrall et al, 2007).…”

Ionic Liquid Extraction Unveils Previously Occluded Humic‐Bound Iron in Peat Soil Pore Water

“…It is likely that changes in DOM character exert varying interference effects on spectrophotometric determination of Fe species in different peatland ecosystems, such as in bogs vs. fens. For example, changes in water residence time and connectivity with groundwater in different peatlands influence DOM character (Hribljan et al, 2014), which likely interacts with changes in alkalinity in governing Fe speciation (Boomer and Bedford, 2008). Therefore, to accurately appreciate the role Fe plays in anaerobic metabolism in bogs and fens it is important to critically evaluate spectrophotometric determination of Fe in the challenging matrix of peat pore water and to identify conditions where spectrophotometric approaches are not suitable.…”