Upland grasslands in Northern England were atmospheric carbon sinks regardless of management regimes

Abstract

Continuous exchange of carbon (C) in the forms of carbon dioxide (CO2) and methane (CH4) occurs between the atmosphere and the terrestrial ecosystem. These greenhouse gases (GHGs) contribute significantly to global warming when present in the atmosphere. Thus, there is growing interest in understanding better ways of managing terrestrial ecosystems so as to increase or fully utilize their capacity to sequester GHGs, or reduce emissions, and mitigate climate change. In this study, we examined the fluxes of CO2 and CH4 in two upland grassland locations (Nidderdale and Ribblesdale) in northern England with contrasting lithologies and under: 1) traditional hay meadow and 2) conventional pasture management. Net ecosystem exchange (NEE) and ecosystem respiration (ER) were measured for 12 months from June 2016 to May 2017, alongside other environmental variables such as soil temperature and moisture, and photosynthetically active radiation (PAR). Results showed that the grasslands were a net atmospheric C sink, with an uptake of 1822–2758 g CO2-eq m−2 year−1. This C uptake is greater than those reported in other European grasslands due to low ER. The Ribblesdale hay meadow had the lowest C uptake (1822 g CO2-eq m−2 year−1) likely due to low available soil nitrogen (N) resulting from the absence of N fertilization. This has implication for agri-environment schemes that discourage the use of inorganic N fertilizers. Warmer condition in Ribblesdale was implicated as the cause of higher C efflux relative to Nidderdale, which has implications for future climate change. The CH4 fluxes were very low (−0.36 to −0.44 g CH4 m−2 year−1) and did not differ significantly between management regimes. It is recommended that future research should prioritise the overall GHG balance of upland grasslands and their inter-annual and decadal variability.