Carbon storage in the meadows

As we examine the results of our biodiversity audit, it seems there's more to the carbon storage in our meadows than we first thought...

By Tim Hitchens

The article I wrote a month ago has produced a fascinating discussion. Our calculation had been that the large majority of our carbon storage in College was in our trees. We set the overall figure at 434 tonnes of carbon. But Dr Tim King, who sits on our Grounds Committee and is an expert in meadows, thinks the figure could be near double that. He judges that the four hectares of Wolfson meadows across the Cherwell river alone store something like 400 tonnes. 

He has been in contact with Emma Rothero from the Floodplain Meadows Partnership (Open University), who works closely with Professor David Gowing, the UK expert (together with Professor Richard Bardgett of Manchester University) on floodplain meadow soils. She confirms that Tim’s suggestion of 400 tonnes of carbon in the meadows is itself almost certainly an underestimate.  This is because it’s based on carbon capture in the top 10cm of the meadows; but recent measurements suggest that the levels are high at least down to 50 cm, 5 times deeper than the calculation. 

Here is a little perspective. Next to peat bogs, flood plain soils store more carbon, far more than forest soils, and much more uniform in depth.  Flood Plain meadows such as Wolfson were regarded for centuries as the most valuable agricultural habitat, providing hay and grazing, continually enriched by annual overflow river water, and managed by complex systems of culverts and ditches, now frequently silted up. We do not know the depth of Wolfson meadow soils but they are probably equivalent to Hinksey Meadow at North Hinksey, next to the Seacourt Stream.  Records for that began in 1011 AD. Archaeological investigations suggest a variable depth of carbon-rich alluvium 1.5 m -0.5 m deep over the gravel. Thus, the carbon storage in the Wolfson meadow soils is likely to be far, far more than in our gardens on the other side of the Cherwell. 

It’s also argued that peat or humus (as in the Wolfson meadow soils) is a more reliable store of carbon than wood, because unless it is preserved in buildings or furniture, tree trunk and root carbon is quickly re-released to the atmosphere.  Floodplain meadows such as Wolfson’s are very active carbon accumulators. The plant root systems can grow to several metres in depth, evenly distributed. Thus, the current scientific idea is that species-rich grasslands should be preserved, whilst any trees should be planted in existing gardens, woodland clearances and wastelands. 

All told this suggests that the College’s grounds store not 434 tonnes of carbon, but nearer to 800 tonnes or more. And the more research is conducted, the better we understand the rich connection between meadows, trees, root systems, and carbon capture in nature.