Linking the molecular composition with peatbog status

Abstract

Peatlands are organic matter rich soils that provide many ecosystem services from carbon storage to water filtration and flood management. Unfortunately, peatlands are fragile systems and as a result of human activities, such as afforestation as well as climate change, a large fraction of global peatlands are damaged. Restoration and protection of peatlands have, therefore, received world-wide attention and multimillion pound investment.

In order to understand if restoration methods are successful we need to investigate the peatland status, which in turn requires an understanding of the processes of peat decomposition and restoration at the molecular level. This work examined two peatlands, a raised bog located at the Red Moss of Balerno (Balerno, Edinburgh) and a blanket bog located in the Flow Country (Caithness and Sutherland) with different ecological status (near natural, drained/damaged, drainblocked/ restored). It was possible to link the molecular structure of those peatlands with their conditions using state-of-the-art spectroscopic techniques, namely Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Nuclear Magnetic Resonance (NMR) spectroscopy, Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) and Laser Desorption Ionization Mass Spectrometry (LDI-MS), and combine the results with traditional parameters, such as vegetation survey, hydrology and bulk peat characteristics. To identify key relationships from the complex data, a number of statistical methods and visualisation tools are required. The combination of both physical and chemical analysis will lead to an accurate evaluation of key indicators related to peatland status that are useful to predict the effects of restoration and contribute to successful restoration strategies.

A detailed molecular-level examination of both liquid and solid phases of one 50 cm peat core, divided into 13 different layers demonstrated the different capabilities of each spectroscopic or spectrometric technique for examining changes occurring with depth and relationships with hydrology or physicochemical factors. Specifically, FT-IR only showed functional group changes with depth irrespective of the position of the water table, while solid and liquid state NMR, detected a correlation between compound classes and water table, in agreement with bulk density. ESI FT-ICR MS of PW-DOM showed higher variation throughout the core than previously reported, demonstrating again the need to examine multiple layers.

A comparison of cores taken from drained and drain-blocked cores from Red Moss of Balerno, indicated that differences do occur on a molecular level, however both ATR-FTIR and solid state 13C NMR data showed that for the solid phase samples there are some differences between each of the cores even from the same site with depth, which hindered clear differences due to health status. Nevertheless, it was possible to detect an increase in alkyl compounds in the restored area at bottom layers, while the damaged site was more characterised by a higher number of O-alkyl fractions until a depth of 15 cm depth.

Differently, the liquid state 1H NMR data showed a clearer difference between the two sites in terms of molecular composition, precisely aromatics are more prevalent in the damaged area, while the restored area is more abundant in carbohydrate compounds. This was explained by specific metabolites, which are able to drive the main differences in the NMR spectra. The ESI FT-ICR MS on PWDOM demonstrated, using the modified aromaticity index, that the restored site has higher plant-derived polyphenols, highly unsaturated and phenolic compounds than the damage area, while there is an opposite trend for aliphatics.

The ATR-FTIR, solid state 13C NMR and LDI MS results about cores taken from the near natural, drained and drain-blocked sites in the Flow Country show a higher content of aliphatic compounds, increasing with depth, in the restored area, while carbohydrates decreased in both near natural and drained sites throughout the cores. Using both liquid state 1H NMR and ESI FT-ICR MS, the cores extracted from these three sites compared to Red Moss indicated that both these kind of peatlands show a similar rising trend of condensed hydrocarbons with depth in PW-DOM on restored sites, precisely an increase of them going down the cores. Then, it can be noted that the lipid content in the solid state phases demonstrated a clear increasing pattern with depth in both restored sites from Flow Country and Red Moss.

Overall, the difference between those two different sites might be attributed to their different nature in which some variables such as pH, vegetation, microbial activities, water content and/or water level play a role in the composition at molecular level. However, despite the investigation of peatlands at molecular level was able to give a great contribution in understanding their status, future work needs to focus on monitoring other key factors that can affect the carbon storage in these ecosystems.