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Title: Nitrogen pollution and the ecology of heather moorland
Author: Edmondson, Jill Louise.
Awarding Body: Manchester Metropolitan University
Current Institution: Manchester Metropolitan University
Date of Award: 2007
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Heather moorlands are of great ecological value and as such are recognised as internationally important habitats. A large proportion of European heather moorland is concentrated within the UK, covering approximately 2-3 million ha" of the UK upland environment. Enhanced levels of N pollution have led to concerns about the eutrophication of many natural and semi-natural ecosystems in the UK, including heather moorland. This study aimed to investigate the response of a moorland ecosystem to artificially enhanced N deposition and the interaction of P with increasing N input. A further aim was to investigate the potential for moorland ecosystem recovery from enhanced N deposition. The research presented within this thesis was part of an ongoing long-term N manipulation experiment established in 1989 on a heather moorland in Wales. This study focussed on a N manipulation experiment established at the site in 1998, where N was added at treatment levels of 0, 10,20,40 and 120kg ha" yr". In addition to this there were Nand P combination treatments, with P added at a rate of 20kg ha" yr". A N recovery experiment was established on the 1998 experimental plots, whereby treatment with N to one half of each plot ceased in 2003, in order to investigate potential for recovery from enhanced N deposition. Cal/una vulgaris growth was stimulated by increasing total N input as was the foliar N concentration. The stimulation of C. vulgaris growth indicates that this species was N limited at ambient levels of deposition. Bryophyte and lichen frequency and cover and bryophyte species diversity were significantly reduced by artificially enhanced N deposition. The foliar N concentration of the dominant moss species Hypnum jutlandicum was elevated with increasing N input. Peat and litter nutrient levels also responded positively to N input, with significant increases in N concentration and exchangeable N. The increase in exchangeable N with N addition demonstrates the increase in bio-available N with enhanced N deposition in moorland ecosystems. The P acquiring enzyme phosphatase and the lignin degrading enzyme phenol oxidase showed no consistent response to N input. The different components within the moorland ecosystem showed varying levels of N, P or N and P co-limitation. The dominant plant species C. vulgaris was clearly N limited at ambient levels of N deposition, as indicated by significant growth stimulation and foliar N accumulation with increased N input. However, P addition did cause a positive growth response in this species, albeit weaker than the response to N input, suggesting a certain degree of Nand P co-limitation. The bryophyte and lichen community were clearly P limited, with P addition significantly increasing bryophyte and lichen frequency and species diversity. Soil microorganisms also displayed some evidence of P limitation as the addition of P, even at ambient N deposition, significantly reduced the activity of phosphatase. The moorland showed little evidence of recovery 2 years after N treatment had ceased. However, there was a significant reduction in litter exchangeable NH4, C. vulgaris total foliar N concentration and C. vulgaris shoot extension. Liverwort cover had increased in those plots where N treatment had ceased. The data from the N recovery experiment suggests that although there was some evidence of recovery, the legacy of N deposition to the experiment may persist for some time. A regional survey in 2005 of moorland sites in Scotland, Wales and the Peak District, was used to investigate whether any of the responses to artificially enhanced N deposition at the N manipulation experiment could be used as bio-indicators of N deposition at a regional scale. Of the bio-indicators tested, litter exchangeable Nand C. vulgaris N:P ratio showed a significant positive association with modelled N deposition. A significant negative association was observed between litter phenol oxidase activity, bryophyte species richness and N deposition. Litter total N concentration and phosphatase activity and C. vulgaris and H. jutlandicum total foliar N concentration did not have a significant association with N deposition. The potential bio-indicators identified are from varying components of the moorland ecosystem (i.e. soil system, bryophytes and C. vulgaris) and consequently may not only provide an indication of ecosystem N status but also overall moorland health in response to varying levels of N deposition.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available