Substrate quality of drained organic soils—Implications for carbon dioxide fluxes

Background: Peatlands only cover a minor fraction of the global terrestrial surface, but due to drainage, they are major contributors to carbon dioxide (CO2) emissions from soils. Previous studies have shown that hydrological conditions, nutrient availability and anthropogenic disturbance play an important role in the mineralisation of organic matter. Furthermore, microbial turnover depends on peat quality, which is determined by its botanical origin and degree of transformation under natural conditions. Aims: The objective of this study was to shed light on the interdependence between mineralisation rates, secondary transformation of peat and chemical composition by examining the differences between bog and fen peat and between strongly degraded topsoil and well-preserved subsoil. Methods: Bog and fen peat from ten different peatlands under grassland use in Germany were analysed for their chemical composition using standard 13C nuclear magnetic resonance (NMR) spectroscopy and wet chemical extractions for fibre analysis. The radiocarbon age was determined as well. The results were combined with CO2 fluxes from a previous incubation study. Results: Topsoils had higher shares of proteins and lipids, and lower shares of carbohydrates and aromatics than subsoils. Bog peat subsoils were characterised by higher shares of carbohydrates and lower shares of aromatics than fen peat subsoils. Topsoils were more similar to each other in their chemical composition than the subsoils. Considering all samples, aromatics and phenolics were negatively correlated with CO2 fluxes. Measured CO2 fluxes from topsoils were significantly higher than from subsoils. However, no influences of chemical composition on CO2 fluxes were detected when examining topsoils and subsoils separately. Even though aromatics and phenolics showed positive relationships with radiocarbon age, differences in age alone were unable to explain the higher amounts of these compounds in the subsoil. Conclusions: The results imply that chemical composition of topsoil peat is not the reason for higher mineralisation rates compared to subsoil peat, but rather a consequence of decomposition and transformation. Thus, peat mineralisation of drained organic soils under agriculture might not slow down over time due to gradually decreasing peat quality but could increase further

How do sand addition, soil moisture and nutrient status influence greenhouse gas fluxes from drained organic soils?

Drainage turns peatlands from natural carbon sinks into hotspots of greenhouse gas (GHG)emissions from soils due to alterations in hydrological and biogeochemical processes. As a consequence of drainage-induced mineralisation and anthropogenic sand addition, large areas of former peatlands under agricultural use have soil organic carbon (SOC)contents at the boundary between mineral and organic soils. Previous research has shown that the variability of GHG emissions increases with anthropogenic disturbance. However, how and whether sand addition affects GHG emissions remains a controversial issue. The aim of this long-term incubation experiment was to assess the influence of hydrological and biogeochemical soil properties on emissions of carbon dioxide (CO 2 ), nitrous oxide (N 2 O)and methane (CH 4 ). Strongly degraded peat with sand addition (peat-sand mixtures)and without sand addition (earthified peat)was systematically compared under different moisture conditions for fen and bog peat. Soil columns originating from both the topsoil and the subsoil of ten different peatlands under grassland use were investigated. Over a period of six months the almost saturated soil columns were drained stepwise via suction to −300 hPa. The CO 2 fluxes were lowest at water-saturated and dry soil moisture conditions, resulting in a parabolic dependence of CO 2 fluxes on the water-filled pore space (WFPS)peaking at 56–92% WFPS. The highest N 2 O fluxes were found at between 73 and 95% WFPS. Maximum CO 2 fluxes were highest from topsoils, ranging from 21 to 77 mg C m −2 h −1 , while the maximum CO 2 fluxes from subsoils ranged from 3 to 14 mg C m −2 h −1 . No systematic influence of peat type or sand addition on GHG emissions was found in topsoils, but CO 2 fluxes from subsoils below peat-sand mixtures were higher than from subsoils below earthified peat. Maximum N 2 O fluxes were highly variable between sites and ranged from 18.5 to 234.9 and from 0.2 to 22.9 μg N m −2 h −1 for topsoils and subsoils, respectively. CH 4 fluxes were negligible even under water-saturated conditions. The highest GHG emissions occurred at a WFPS that relates – under equilibrium conditions – to a water table of 20–60 cm below the surface in the field. High maximum CO 2 and N 2 O fluxes were linked to high densities of plant-available phosphorus and potassium. The results of this study highlight that nutrient status plays a more important role in GHG emissions than peat type or sand addition, and do not support the idea of peat-sand mixtures as a mitigation option for GHG emissions

Substrate quality of drained organic soils – Implications for carbon dioxide fluxes

Supplementary data to the paper "Substrate quality of drained organic soils – Implications for carbon dioxide fluxes" by A.Säurich, B.Tiemeyer, U. Dettmann, S. Fiedler and A. Do

Drained organic soils under agriculture — The more degraded the soil the higher the specific basal respiration

status: publishe