Top soil removal reduces water pollution from phosphorus and dissolved organic matter and lowers methane emissions from rewetted peatlands

Abstract

A valid strategy to mitigate the eutrophication of water bodies due to non‐point source phosphorus (P) pollution and to reduce the emissions of greenhouse gases is the rewetting of degraded peatlands. However, long‐term drainage and intensive agricultural use make it unlikely that the original sink functions for nutrients and carbon (C) as well as low‐nutrient conditions can be re‐established within a human time perspective. We hypothesized that the removal of the upper degraded peat layer can be a suitable measure to avoid the negative implications of excess mobilization of P and C after rewetting. To evaluate the effect of top soil removal (TSR) we performed lab and field experiments in six inundated peatlands in northern Germany without TSR compared to six inundated sites with TSR. In addition, we included data from a rewetted peatland where the degraded peat had been removed from about half of the area and groundwater level was just beneath the soil surface. The results emphasized that following inundation newly formed detritus mud layers overlying the former peat surface are the dominating source for P and methane in particular in sites without TSR but also in sites with TSR, although at significantly lower rates. Although highly decomposed peat released more or less no methane, dissolved organic matter mobilization was highest in this substrate while less decomposed peat was characterized in general by lowest rates of mobilization. Synthesis and applications. Top soil removal prior to rewetting can be a suitable method to avoid the negative consequences of the excess release of phosphorus (P) and carbon post‐rewetting. We developed a simple decision support schematic to assist the peatland restoration process and to better understand the implications of top soil removal. Despite the potential benefits, top soil removal should not be declared as a universal method, as it requires detailed consideration prior to application. However, this and other research demonstrate that it is inevitable that without any further management interventions high mobilization of P, dissolved organic matter and methane may persist for centuries following rewetting of peatlands.

Rewetting of Three Drained Peatlands Drives Congruent Compositional Changes in Pro- and Eukaryotic Soil Microbiomes through Environmental Filtering

“…vertical distribution in the soil profile (reviewed in [6]) and corroborates recent findings from other ecosystems [54,55]. This observation makes peatland management practices such as top soil removal attractive for mitigation of CH4 emissions from peatlands [56,57]. The abundance of methanogens was strongly correlated with soil water content ( Figure S2), which drives anoxia in the soil.…”

From Understanding to Sustainable Use of Peatlands: The WETSCAPES Approach

“…Furthermore, seasonal temperature variation, predominant plant species, soil and water chemistry all influence the plant nutrient status of peatlands [54,56,57]. Removing degraded peat surface layers has been recommended to decrease nutrient stocks to accelerate restoration of degraded peatlands [28,58]. A nutrient-rich peat layer, however, may also enhance peat formation and lead to high carbon sequestration [54].…”

Soil degradation determines release of nitrous oxide and dissolved organic carbon from peatlands

“…Higher DOC concentrations in highly decomposed and degraded peat (especially under restoration) are probably related to the dissolution of redox-sensitive Fe(III)-OM compounds and to some extent also to the lowered hydraulic conductivities (Zak and Gelbrecht 2007). During drainage and peat mineralization refractory, OM compounds are accumulated due to chemical binding of amorphous and more crystalline ferric compounds, also formed under oxic drained conditions (Zak et al 2018). The expected duration of the suspected DOC mobilization caused by iron reduction or other biogeochemical processes after rewetting of degradation of peatlands is uncertain.…”

“…Although the OM quality in peat is supposedly a depth-dependent property (Leifeld et al 2012, Zaccone et al 2017), the generated dataset revealed no correlation between the elemental ratios (O/C and H/C) and soil sampling depths (Pearson's correlation coefficient, r<0.1; p>0.05). In a natural state, BD is expected to increase with depth, while with progressing degradation, the top soil becomes more compacted(Zak and Gelbrecht 2007, Liu and.…”