Estimated emissions from peat soils in the Broads

Holman, Ian; Girkin, Nicholas; Truckell, Ian

Abstract

This report describes work commissioned by the Broads Authority and carried out by Cranfield University to improve the accuracy of estimates of past wastage by installing rust rods and surface rods to monitor peat wastage and to estimate carbon dioxide (CO2) and methane (CH4) emissions from peat stocks.

36 sets of rust rods and surface rods were installed across 5 peatland sites between 11th-13th and 19th-20th April 2022 to cover a range of landuses (grassland, woodland and fen) and drain water levels (low,
medium and high). The sites were re-visited on the 5th-6th October 2022 following the exceptionally hot and dry summer to measure the rust lines and the watertable depth.

The estimated depths of the orange rust (iron oxide) on the rust rods were (within the exception of a single rod) deeper than the watertable measured in adjacent auger hole, with a median difference of about 5 cm (but up to +/-23 cm). Duplicate sets of rods installed at one peatland site showed broadly consistent rust deposits when installed close together, suggesting results are broadly replicable.

The estimates of carbon dioxide (CO2) and methane (CH4) emissions from peat stocks in the Broads were derived from a novel method that integrated a Lidar-based approach to estimating drain water levels and drain freeboard (height difference between the drain water level and the field); spatial analysis of field geometry, daily watertable modelling and the application of pre-existing regressions equations between mean effective watertable depth and emissions. The methodology was applied to the area of peat soils from Heppell et al. (2020) updated by the Broads Authority in 2023. The method was validated against Environment Agency gauge board data, IDB pump on-off levels and Environment Agency shallow dipwell monitoring data.

The total CO2 balance and CH4 flux from the peat soils of the Broads National Park were estimated at 17,866 tC/yr (uncertainty range of 3302 – 32,522 tC/yr) and 693 tC/yr (uncertainty range of 347 – 1,041 tC/yr), respectively.

Using a 100-year Global Warming Potential for CH4 of 27.9, the total radiative forcing from emissions of the two gases is estimated at 91,389 t CO2eq/yr (uncertainty range of 25,049 – 158,068 t CO2eq/yr), of which 72% is associated with CO2 and 28% with CH4 emissions.

This report has, for the first time, provided a high resolution spatial assessment of estimated greenhouse gas emissions from the peats in The Broads, that takes account of land cover, watertable depth and weather. It suggests that the peats of the Broads are associated with highly spatially varying carbon emissions in the form of CO2 from drained areas and CO2 and CH4 from semi-natural areas, but with the lowest emissions and climate forcings generally from fen habitat and the highest from agricultural areas.

Citation

Holman, I., Girkin, N., & Truckell, I. (2023). Estimated emissions from peat soils in the Broads. Broads Authority

• Report Type: Project Report
• Publication Date: 2023-04
• Deposit Date: Nov 28, 2023
• Publicly Available Date: Nov 29, 2023
• Public URL: https://nottingham-repository.worktribe.com/output/27861054
• Publisher URL: https://www.broads-authority.gov.uk/__data/assets/pdf_file/0031/482962/Estimated-emissions-from-peat-soils-in-the-Broads-National-Park-2023.pdf
• Additional Information: © Crown copyright [and database rights] 2023 OS 100021573. You are granted a non-exclusive, royalty free, revocable licence solely to view the Licensed Data for non-commercial purposes for the period during which the Broads Authority makes it available. You are not permitted to copy, sub-license, distribute, sell or otherwise make available the Licensed Data to third parties in any form. Third party rights to enforce the terms of this licence shall be reserved to OS.