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Carbon storage
Carbon storage
The Importance of Peatlands to the Tyne Catchment
Courtesy of Dr. Rob Spencer
To many people one of their favourite areas within the Tyne catchment is the untamed beauty of the peat uplands. These peat uplands in the Cheviot Hills and the Cumbrian Pennines give birth to the North and South Tyne respectively and combine as the River Tyne just upstream of Hexham. Peatlands play a very important role in the sequestration of carbon from the atmosphere and as such any decline in the extent of peatlands impacts on the global carbon cycle. Furthermore, peatlands are the highest areas of terrestrial carbon storage in the U.K. and act like a reservoir of terrestrial carbon and so clearly any factor which might result in the release of such large quantities of carbon must be monitored with great concern.
In fact a number of studies in recent years have highlighted increasing organic carbon export from U.K. catchments and rivers (e.g. a 65% increase in dissolved organic carbon concentration was observed in upland catchments in the U.K. between 1988-2001) which has been linked to global climate change. The rate of various enzyme controlled reactions in peatlands are controlled by temperature with decomposition rates generally becoming slower with cooling and enhanced by warming and so rising temperatures can potentially stimulate an increase in organic carbon flux. Global climate change is predicted to lead to generally warmer and wetter conditions for the U.K. and so it seems will result in increased decomposition and export of terrestrial carbon stores, particularly peatlands. To see U.K. peatlands literally washed out to sea such as those in the Tyne catchment is an ominous enough thought, but it seems likely the story has a further sting in the tail to unfortunately help speed things along.
At a compositional level organic material in the Tyne is highly similar to that found in peatland derived Arctic Rivers and recent studies have shown that this organic material is relatively resistant to microbial degradation and so reaches the oceans with little modification. However, this peatland derived organic material is highly photochemically reactive and in the optically clearer waters of the oceans is broken down. Amongst the many degradation products is carbon dioxide which is an important greenhouse gas and so results in further forcing of global climate change. This will likely result in a positive feedback mechanism thus speeding up global climate change and increasing the flux of peatland carbon to the oceans and subsequently the atmosphere.
Tackling the issue of global climate change is complicated and although we can all make an effort it also requires strong dedication from those in charge of national and international environmental policy. As a Trust to protect the Tyne River and catchment however it is prudent to be aware of other factors which have potential to impact negatively on peatlands. U.K. peatlands face a number of threats such as peat harvesting for energy and horticulture and also drainage for forestry and other land conversions. Typically in the U.K. peatlands drained for afforestation results in the aeration of the top 60-70cm (in summer months) of soil and water utilisation by trees lowers the water table further.
Following drainage peatlands undergo oxidation and due to forest rotations and repeated drainage this results in an increase in the export of peat derived carbon and leaves the most resistant material behind and so fundamentally changes the type of carbon exported. Research has shown changes in the quantity and quality of the organic material exported by rivers frequently results in a number of negative impacts as a whole for the catchment. For example, concentration and composition of organic matter has been shown to have important effects with respect to its role in the natural environment and this material plays important roles in aquatic food webs, mediates light in the water column, is of key importance with respect to carbon dynamics, nutrient budgets, complexation of trace metals and the mobilisation of pollutants. It also impacts on the suitability for extraction of drinking waters as production of carcinogens on chlorination such as trihalomethanes has been shown to be related to organic matter concentration and composition.
Additionally in a study conducted in northern Finland the recapture rates of stocked yearling salmon were lower in areas impacted by peat mining and forest drainage than in pristine areas. The salmon caught from the impacted areas were also smaller and thinner by the end of the summer than those from pristine reaches of the same river. To maintain a healthy Tyne catchment it seems imperative to care for the peatlands and minimise the disturbance that they suffer. As the source of the Tyne Rivers the protection of the upland peat areas is one of the most prudent ways to continue to improve and maintain the water quality and health of the River as well as the natural beauty of the region.
