DOC and CO₂-C Releases from Pristine and Drained Peat Soils in Response to Water Table Fluctuations: A Mesocosm Experiment

Abstract

Hydrological conditions are considered to be among the main drivers influencing the export of dissolved organic carbon (DOC) from terrestrial to aquatic ecosystems, and hydrology is likely to alter due to climate change. We built a mesocosm experiment by using peat profiles from a pristine and from a drained (drained in 1978) peatland. A several-week-long low water table period followed by a high water table period, that is, a setting mimicking drought followed by flood, released relatively more DOC from pristine peat than from drained peat. From pristine peat profiles DOC was released into soil water in such quantities that the concentration of DOC remained stable despite dilution caused by added spring water to the mesocosms. In drained peat the DOC concentrations decreased during the high water table period indicating stronger dilution effect in comparison to pristine peat. At the landscape level DOC load from a drained peatland to the recipient water body may, however, increase during flooding because of high water runoff out of the peatland containing high DOC concentrations relative to the forest and agricultural areas. During the high water table period neither peat type nor water table had any clear impact on carbon dioxide (CO2-C) fluxes.

Effect of land cover and hydro‐meteorological controls on soil water DOC concentrations in a high‐elevation tropical environment

“…Under all the studied land cover types, high soil moisture contents led to low DOC concentrations. The general decrease of DOC concentrations with increasing soil moisture content (i.e., wetter periods) likely results from the mobilization, washout, and dilution of DOC that was produced previously during periods of low soil moisture conditions (i.e., drier periods), since microbial activity is expected to enhance under an higher oxygen concentrations and higher temperatures (Bowden, Davidson, Savage, Arabia, & Steudler, 2004;Laine et al, 2014;Tipping et al, 1999). In addition, high soil moisture (commonly above field capacity and near saturation) is also likely to produce an increase in shallow subsurface flow in Páramo soils (Mosquera, Célleri, et al, 2016).…”

“…In peat dominated ecosystems such as the Páramo, changes in rainfall and temperature fluctuations as well as LC/LU changes are directly and strongly related to soil carbon losses (Freeman, Evans, & Monteith, 2001;Rixen, Baum, Wit, & Samiaji, 2016). The impact of a number of climatic and LC/LU related factors (e.g., temperature increase, deforestation, or droughts), which influence dissolved organic carbon (DOC) mobilization, has already been observed in other ecosystems in temperate regions (Borken, Ahrens, Schulz, & Zimmermann, 2011;Freeman et al, 2001;Laine, Strömmer, & Arvola, 2014;Sarkkola et al, 2009;Stutter, Langan, & Cooper, 2008). Any imbalance to the carbon cycle caused by such factors not only potentially leads to increased carbon mobilization rates but also to a potentially lower carbon sequestration capacity of the Páramo soils.…”

The impact of long-term water level draw-down on microbial biomass: A comparative study from two peatland sites with different nutrient status

“…Also, since drainage effect on microbial communities in deeper anoxic layers depends on the movement of materials (e.g. DOC) from the surface to deeper layers [24,26,27], accumulation of materials to concentration able to cause significant changes in microbial biomass is more probable in the deepest layers than in the intermediate layers, many years after drainage [24].…”

“…The total microbial PLFA biomass at the bottom layers of the drained and natural sites were different in both sites. This was due to changes in the flow and constituent of the leachate water [24], deeper deposition of labile root exudates by vascular plants and differences in the amount and quality of DOC reaching the bottom layers in the drained sites [26,27]. Although the roots of vascular plants may not reach the bottom layers, their root exudates will get deeper and influence microbes in the bottom layers, via water movement, faster than those deposited by the shallow roots of mosses.…”

“…However, the drainage-induced higher oxygenation coupled with temperature change in the surface layers could prompt DOC release to deeper depths via the "enzymatic latch" process [23]. This increase in the amount (flow) and quality of dissolved organic C (DOC) [24], coupled with deeper deposition of labile root exudates by roots of vascular plants [25][26][27] could modify the microbial communities (biomass and composition) in deeper peatland layers. Recent molecular evidence and the higher bulk peat stable C isotope (δ 13 C) values (qualitative indicator of peatland degradation; with the associated fractionation) in the bottom of drained peat, supports this view [17,28].…”